ASP.NET Core中Options模式的使用及其源码解析

在ASP.NET Core中引入了Options这一使用配置方式，其主要是为了解决依赖注入时需要传递指定数据问题（不是自行获取，而是能集中配置）。通常来讲我们会把所需要的配置通过IConfiguration对象配置成一个普通的类，并且习惯上我们会把这个类的名字后缀加上Options。所以我们在使用某一个中间件或者使用第三方类库时，经常会看到配置对应的Options代码，例如：关于Cookie的中间件就会配置CookiePolicyOptions这个对象。

1、Options模式的用法

向服务容器中注入TOptions配置（绑定配置）：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
using IConfiguration_IOptions_Demo.Models;

namespace IConfiguration_IOptions_Demo
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }

        public IConfiguration Configuration { get; }

        // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {
            #region Options模式

            services.PostConfigureAll<AppSettingsOptions>(options => options.Title = "PostConfigureAll");

            services.Configure<AppSettingsOptions>(Configuration);
            services.Configure<OtherConfig>(Configuration.GetSection("OtherConfig"));
            services.Configure<AppSettingsOptions>(options => options.Title = "Default Name");//默认名称string.Empty

            services.Configure<AppSettingsOptions>("FromMemory", options => options.Title = "FromMemory");
            services.AddOptions<AppSettingsOptions>("AddOption").Configure(options => options.Title = "AddOptions");
            services.Configure<OtherConfig>("FromConfiguration", Configuration.GetSection("OtherConfig"));

            services.ConfigureAll<AppSettingsOptions>(options => options.Title = "ConfigureAll");
            services.PostConfigure<AppSettingsOptions>(options => options.Title = "PostConfigure");

            #endregion Options模式

            services
                .AddControllersWithViews()
                .AddRazorRuntimeCompilation() //修改cshtml后能自动编译
                .AddNewtonsoftJson(options =>
                {
                    options.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;//忽略循环引用
                    options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore;//序列化忽略null和空字符串
                    options.SerializerSettings.MissingMemberHandling = MissingMemberHandling.Ignore;
                    options.SerializerSettings.ContractResolver = new DefaultContractResolver();//不使用驼峰样式的key
                });
        }

        // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
            }
            app.UseStaticFiles();

            app.UseRouting();

            app.UseAuthorization();

            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllerRoute(
                    name: "default",
                    pattern: "{controller=Home}/{action=Index}/{id?}");
            });
        }
    }
}

从服务容器中获取TOptions对象（读取配置）：

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Options;

using IConfiguration_IOptions_Demo.Models;
using Newtonsoft.Json;
using System.Text;

namespace IConfiguration_IOptions_Demo.Controllers
{
    public class OptionsDemoController : Controller
    {
        protected readonly IOptions<AppSettingsOptions> _options; //直接单例，不支持数据变化，性能高
        protected readonly IOptionsMonitor<AppSettingsOptions> _optionsMonitor; //支持数据修改，靠的是监听文件更新(onchange)数据（修改配置文件会更新缓存）
        protected readonly IOptionsSnapshot<AppSettingsOptions> _optionsSnapshot; //一次请求数据不变的，但是不同请求可以不同的，每次生成
        protected readonly IOptions<OtherConfig> _optionsOtherConfig;

        public OptionsDemoController(
            IOptions<AppSettingsOptions> options, 
            IOptionsMonitor<AppSettingsOptions> optionsMonitor, 
            IOptionsSnapshot<AppSettingsOptions> optionsSnapshot,
            IOptions<OtherConfig> optionsOtherConfig)
        {
            _options = options;
            _optionsMonitor = optionsMonitor;
            _optionsSnapshot = optionsSnapshot;
            _optionsOtherConfig = optionsOtherConfig;
        }

        public IActionResult Index()
        {
            var sb = new StringBuilder();
            AppSettingsOptions options1 = _options.Value;
            OtherConfig otherConfigOptions1 = _optionsOtherConfig.Value;

            sb.AppendLine($"_options.Value => {JsonConvert.SerializeObject(options1)}");
            sb.AppendLine("");
            sb.AppendLine($"_optionsOtherConfig.Value => {JsonConvert.SerializeObject(otherConfigOptions1)}");

            AppSettingsOptions options2 = _optionsMonitor.CurrentValue; //_optionsMonitor.Get(Microsoft.Extensions.Options.Options.DefaultName);
            AppSettingsOptions fromMemoryOptions2 = _optionsMonitor.Get("FromMemory"); //命名选项

            sb.AppendLine("");
            sb.AppendLine($"_optionsMonitor.CurrentValue => {JsonConvert.SerializeObject(options2)}");
            sb.AppendLine("");
            sb.AppendLine($"_optionsMonitor.Get(\"FromMemory\") => {JsonConvert.SerializeObject(fromMemoryOptions2)}");

            AppSettingsOptions options3 = _optionsSnapshot.Value; //_optionsSnapshot.Get(Microsoft.Extensions.Options.Options.DefaultName);
            AppSettingsOptions fromMemoryOptions3 = _optionsSnapshot.Get("FromMemory"); //命名选项

            sb.AppendLine("");
            sb.AppendLine($"_optionsSnapshot.Value => {JsonConvert.SerializeObject(options3)}");
            sb.AppendLine("");
            sb.AppendLine($"_optionsSnapshot.Get(\"FromMemory\") => {JsonConvert.SerializeObject(fromMemoryOptions3)}");
            return Content(sb.ToString());
        }
    }
}

访问 “/OptionsDemo/Index” 运行结果如下所示：

2、Options模式源码解析

我们从下面的这条语句开始分析：

services.Configure<AppSettingsOptions>(options => options.Title = "Default Name");

将光标移动到 Configure 然后按 F12 转到定义，如下：

可以发现此 Configure 是个扩展方法，位于 OptionsServiceCollectionExtensions 类中，我们找到 OptionsServiceCollectionExtensions 类的源码如下：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using Microsoft.Extensions.DependencyInjection.Extensions;
using Microsoft.Extensions.Options;

namespace Microsoft.Extensions.DependencyInjection
{
    /// <summary>
    /// Extension methods for adding options services to the DI container.
    /// </summary>
    public static class OptionsServiceCollectionExtensions
    {
        /// <summary>
        /// Adds services required for using options.
        /// </summary>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection AddOptions(this IServiceCollection services)
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptions<>), typeof(OptionsManager<>)));
            services.TryAdd(ServiceDescriptor.Scoped(typeof(IOptionsSnapshot<>), typeof(OptionsManager<>)));
            services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitor<>), typeof(OptionsMonitor<>)));
            services.TryAdd(ServiceDescriptor.Transient(typeof(IOptionsFactory<>), typeof(OptionsFactory<>)));
            services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitorCache<>), typeof(OptionsCache<>)));
            return services;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure{TOptions}(IServiceCollection, Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection Configure<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
            => services.Configure(Options.Options.DefaultName, configureOptions);

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure{TOptions}(IServiceCollection, Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="name">The name of the options instance.</param>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions)
            where TOptions : class
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            services.AddOptions();
            services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(name, configureOptions));
            return services;
        }

        /// <summary>
        /// Registers an action used to configure all instances of a particular type of options.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection ConfigureAll<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
            => services.Configure(name: null, configureOptions: configureOptions);

        /// <summary>
        /// Registers an action used to initialize a particular type of options.
        /// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection PostConfigure<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
            => services.PostConfigure(Options.Options.DefaultName, configureOptions);

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configure.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="name">The name of the options instance.</param>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection PostConfigure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions)
            where TOptions : class
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            services.AddOptions();
            services.AddSingleton<IPostConfigureOptions<TOptions>>(new PostConfigureOptions<TOptions>(name, configureOptions));
            return services;
        }

        /// <summary>
        /// Registers an action used to post configure all instances of a particular type of options.
        /// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection PostConfigureAll<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
            => services.PostConfigure(name: null, configureOptions: configureOptions);

        /// <summary>
        /// Registers a type that will have all of its I[Post]ConfigureOptions registered.
        /// </summary>
        /// <typeparam name="TConfigureOptions">The type that will configure options.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection ConfigureOptions<TConfigureOptions>(this IServiceCollection services) where TConfigureOptions : class
            => services.ConfigureOptions(typeof(TConfigureOptions));

        private static bool IsAction(Type type)
            => (type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition() == typeof(Action<>));

        private static IEnumerable<Type> FindIConfigureOptions(Type type)
        {
            var serviceTypes = type.GetTypeInfo().ImplementedInterfaces
                .Where(t => t.GetTypeInfo().IsGenericType && 
                (t.GetGenericTypeDefinition() == typeof(IConfigureOptions<>)
                || t.GetGenericTypeDefinition() == typeof(IPostConfigureOptions<>)));
            if (!serviceTypes.Any())
            {
                throw new InvalidOperationException(
                    IsAction(type)
                    ? Resources.Error_NoIConfigureOptionsAndAction
                    : Resources.Error_NoIConfigureOptions);
            }
            return serviceTypes;
        }

        /// <summary>
        /// Registers a type that will have all of its I[Post]ConfigureOptions registered.
        /// </summary>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="configureType">The type that will configure options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection ConfigureOptions(this IServiceCollection services, Type configureType)
        {
            services.AddOptions();
            var serviceTypes = FindIConfigureOptions(configureType);
            foreach (var serviceType in serviceTypes)
            {
                services.AddTransient(serviceType, configureType);
            }
            return services;
        }

        /// <summary>
        /// Registers an object that will have all of its I[Post]ConfigureOptions registered.
        /// </summary>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="configureInstance">The instance that will configure options.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection ConfigureOptions(this IServiceCollection services, object configureInstance)
        {
            services.AddOptions();
            var serviceTypes = FindIConfigureOptions(configureInstance.GetType());
            foreach (var serviceType in serviceTypes)
            {
                services.AddSingleton(serviceType, configureInstance);
            }
            return services;
        }

        /// <summary>
        /// Gets an options builder that forwards Configure calls for the same <typeparamref name="TOptions"/> to the underlying service collection.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <returns>The <see cref="OptionsBuilder{TOptions}"/> so that configure calls can be chained in it.</returns>
        public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services) where TOptions : class
            => services.AddOptions<TOptions>(Options.Options.DefaultName);

        /// <summary>
        /// Gets an options builder that forwards Configure calls for the same named <typeparamref name="TOptions"/> to the underlying service collection.
        /// </summary>
        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="name">The name of the options instance.</param>
        /// <returns>The <see cref="OptionsBuilder{TOptions}"/> so that configure calls can be chained in it.</returns>
        public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services, string name)
            where TOptions : class
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            services.AddOptions();
            return new OptionsBuilder<TOptions>(services, name);
        }
    }
}

仔细阅读上面的源码后可以发现，Configure方法虽然有多个重载，但最终都会调用下面的这个方法：

/// <summary>
/// Registers an action used to configure a particular type of options.
/// Note: These are run before all <seealso cref="PostConfigure{TOptions}(IServiceCollection, Action{TOptions})"/>.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="name">The name of the options instance.</param>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions)
    where TOptions : class
{
    if (services == null)
    {
        throw new ArgumentNullException(nameof(services));
    }

    if (configureOptions == null)
    {
        throw new ArgumentNullException(nameof(configureOptions));
    }

    services.AddOptions();
    services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(name, configureOptions));
    return services;
}

Configure方法的多个重载主要差异在于name参数值的不同。当不传递name参数值时，默认使用Microsoft.Extensions.Options.Options.DefaultName，它等于string.Empty，如下所示：

/// <summary>
/// Registers an action used to configure a particular type of options.
/// Note: These are run before all <seealso cref="PostConfigure{TOptions}(IServiceCollection, Action{TOptions})"/>.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection Configure<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
    => services.Configure(Options.Options.DefaultName, configureOptions);

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Helper class.
    /// </summary>
    public static class Options
    {
        /// <summary>
        /// The default name used for options instances: "".
        /// </summary>
        public static readonly string DefaultName = string.Empty;

        /// <summary>
        /// Creates a wrapper around an instance of <typeparamref name="TOptions"/> to return itself as an <see cref="IOptions{TOptions}"/>.
        /// </summary>
        /// <typeparam name="TOptions">Options type.</typeparam>
        /// <param name="options">Options object.</param>
        /// <returns>Wrapped options object.</returns>
        public static IOptions<TOptions> Create<TOptions>(TOptions options) where TOptions : class, new()
        {
            return new OptionsWrapper<TOptions>(options);
        }
    }
}

另外，我们可以看到ConfigureAll这个方法，此方法的内部也是调用Configure方法，只不过把name值设置成null，后续在创建TOptions时，会把name值为null的Action<TOptions>应用于所有的TOptions实例。如下：

/// <summary>
/// Registers an action used to configure all instances of a particular type of options.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection ConfigureAll<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
    => services.Configure(name: null, configureOptions: configureOptions);

至此我们大概知道了，其实Configure方法主要就是做两件事：

1、调用 services.AddOptions() 方法。

2、将 new ConfigureNamedOptions<TOptions>(name, configureOptions) 注册给 IConfigureOptions<TOptions> 。

此外，从 OptionsServiceCollectionExtensions 类的源码中我们可以发现PostConfigure方法同样有多个重载，并且最终都会调用下面的这个方法：

/// <summary>
/// Registers an action used to configure a particular type of options.
/// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
/// </summary>
/// <typeparam name="TOptions">The options type to be configure.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="name">The name of the options instance.</param>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection PostConfigure<TOptions>(this IServiceCollection services, string name, Action<TOptions> configureOptions)
    where TOptions : class
{
    if (services == null)
    {
        throw new ArgumentNullException(nameof(services));
    }

    if (configureOptions == null)
    {
        throw new ArgumentNullException(nameof(configureOptions));
    }

    services.AddOptions();
    services.AddSingleton<IPostConfigureOptions<TOptions>>(new PostConfigureOptions<TOptions>(name, configureOptions));
    return services;
}

与Configure方法一样，PostConfigure方法的多个重载主要差异在于name参数值的不同。当不传递name参数值时，默认使用Microsoft.Extensions.Options.Options.DefaultName，它等于string.Empty，如下：

/// <summary>
/// Registers an action used to initialize a particular type of options.
/// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection PostConfigure<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
    => services.PostConfigure(Options.Options.DefaultName, configureOptions);

同样的，PostConfigureAll方法的内部也是调用PostConfigure方法，只不过把name值设置成null，如下：

/// <summary>
/// Registers an action used to post configure all instances of a particular type of options.
/// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection PostConfigureAll<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
    => services.PostConfigure(name: null, configureOptions: configureOptions);

至此我们可以发现，PostConfigure方法同样也是只做两件事：

1、调用 services.AddOptions() 方法。

2、将 new PostConfigureOptions<TOptions>(name, configureOptions) 注册给 IPostConfigureOptions<TOptions> 。

其实PostConfigure方法，它和Configure方法使用方式一模一样，也是在创建TOptions时调用。只不过先后顺序不一样，PostConfigure在Configure之后调用，该点在后面的讲解中会再次提到。

另外，还有一种AddOptions的用法，如下所示：

services.AddOptions<AppSettingsOptions>("AddOption").Configure(options => options.Title = "AddOptions");

/// <summary>
/// Gets an options builder that forwards Configure calls for the same <typeparamref name="TOptions"/> to the underlying service collection.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <returns>The <see cref="OptionsBuilder{TOptions}"/> so that configure calls can be chained in it.</returns>
public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services) where TOptions : class
    => services.AddOptions<TOptions>(Options.Options.DefaultName);

/// <summary>
/// Gets an options builder that forwards Configure calls for the same named <typeparamref name="TOptions"/> to the underlying service collection.
/// </summary>
/// <typeparam name="TOptions">The options type to be configured.</typeparam>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <param name="name">The name of the options instance.</param>
/// <returns>The <see cref="OptionsBuilder{TOptions}"/> so that configure calls can be chained in it.</returns>
public static OptionsBuilder<TOptions> AddOptions<TOptions>(this IServiceCollection services, string name)
    where TOptions : class
{
    if (services == null)
    {
        throw new ArgumentNullException(nameof(services));
    }

    services.AddOptions();
    return new OptionsBuilder<TOptions>(services, name);
}

这种方式会创建一个OptionsBuilder对象，用来辅助配置TOptions对象，我们找到OptionsBuilder类的源码如下：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using Microsoft.Extensions.DependencyInjection;

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Used to configure <typeparamref name="TOptions"/> instances.
    /// </summary>
    /// <typeparam name="TOptions">The type of options being requested.</typeparam>
    public class OptionsBuilder<TOptions> where TOptions : class
    {
        private const string DefaultValidationFailureMessage = "A validation error has occured.";

        /// <summary>
        /// The default name of the <typeparamref name="TOptions"/> instance.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The <see cref="IServiceCollection"/> for the options being configured.
        /// </summary>
        public IServiceCollection Services { get; }

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="services">The <see cref="IServiceCollection"/> for the options being configured.</param>
        /// <param name="name">The default name of the <typeparamref name="TOptions"/> instance, if null <see cref="Options.DefaultName"/> is used.</param>
        public OptionsBuilder(IServiceCollection services, string name)
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            Services = services;
            Name = name ?? Options.DefaultName;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
        /// </summary>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Configure(Action<TOptions> configureOptions)
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(Name, configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep">A dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Configure<TDep>(Action<TOptions, TDep> configureOptions)
            where TDep : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IConfigureOptions<TOptions>>(sp =>
                new ConfigureNamedOptions<TOptions, TDep>(Name, sp.GetRequiredService<TDep>(), configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Configure<TDep1, TDep2>(Action<TOptions, TDep1, TDep2> configureOptions)
            where TDep1 : class
            where TDep2 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IConfigureOptions<TOptions>>(sp =>
                new ConfigureNamedOptions<TOptions, TDep1, TDep2>(Name, sp.GetRequiredService<TDep1>(), sp.GetRequiredService<TDep2>(), configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Configure<TDep1, TDep2, TDep3>(Action<TOptions, TDep1, TDep2, TDep3> configureOptions)
            where TDep1 : class
            where TDep2 : class
            where TDep3 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IConfigureOptions<TOptions>>(
                sp => new ConfigureNamedOptions<TOptions, TDep1, TDep2, TDep3>(
                    Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the action.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Configure<TDep1, TDep2, TDep3, TDep4>(Action<TOptions, TDep1, TDep2, TDep3, TDep4> configureOptions)
            where TDep1 : class
            where TDep2 : class
            where TDep3 : class
            where TDep4 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IConfigureOptions<TOptions>>(
                sp => new ConfigureNamedOptions<TOptions, TDep1, TDep2, TDep3, TDep4>(
                    Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    sp.GetRequiredService<TDep4>(),
                    configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the action.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the action.</typeparam>
        /// <typeparam name="TDep5">The fifth dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Configure<TDep1, TDep2, TDep3, TDep4, TDep5>(Action<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5> configureOptions)
            where TDep1 : class
            where TDep2 : class
            where TDep3 : class
            where TDep4 : class
            where TDep5 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IConfigureOptions<TOptions>>(
                sp => new ConfigureNamedOptions<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5>(
                    Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    sp.GetRequiredService<TDep4>(),
                    sp.GetRequiredService<TDep5>(),
                    configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure(Action{TOptions})"/>.
        /// </summary>
        /// <param name="configureOptions">The action used to configure the options.</param>
        public virtual OptionsBuilder<TOptions> PostConfigure(Action<TOptions> configureOptions)
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddSingleton<IPostConfigureOptions<TOptions>>(new PostConfigureOptions<TOptions>(Name, configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to post configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep">The dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> PostConfigure<TDep>(Action<TOptions, TDep> configureOptions)
            where TDep : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IPostConfigureOptions<TOptions>>(sp =>
                new PostConfigureOptions<TOptions, TDep>(Name, sp.GetRequiredService<TDep>(), configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to post configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2>(Action<TOptions, TDep1, TDep2> configureOptions)
            where TDep1 : class
            where TDep2 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IPostConfigureOptions<TOptions>>(sp =>
                new PostConfigureOptions<TOptions, TDep1, TDep2>(Name, sp.GetRequiredService<TDep1>(), sp.GetRequiredService<TDep2>(), configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to post configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3>(Action<TOptions, TDep1, TDep2, TDep3> configureOptions)
            where TDep1 : class
            where TDep2 : class
            where TDep3 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IPostConfigureOptions<TOptions>>(
                sp => new PostConfigureOptions<TOptions, TDep1, TDep2, TDep3>(
                    Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to post configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the action.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3, TDep4>(Action<TOptions, TDep1, TDep2, TDep3, TDep4> configureOptions)
            where TDep1 : class
            where TDep2 : class
            where TDep3 : class
            where TDep4 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IPostConfigureOptions<TOptions>>(
                sp => new PostConfigureOptions<TOptions, TDep1, TDep2, TDep3, TDep4>(
                    Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    sp.GetRequiredService<TDep4>(),
                    configureOptions));
            return this;
        }

        /// <summary>
        /// Registers an action used to post configure a particular type of options.
        /// Note: These are run after all <seealso cref="Configure(Action{TOptions})"/>.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the action.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the action.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the action.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the action.</typeparam>
        /// <typeparam name="TDep5">The fifth dependency used by the action.</typeparam>
        /// <param name="configureOptions">The action used to configure the options.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> PostConfigure<TDep1, TDep2, TDep3, TDep4, TDep5>(Action<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5> configureOptions)
            where TDep1 : class
            where TDep2 : class
            where TDep3 : class
            where TDep4 : class
            where TDep5 : class
        {
            if (configureOptions == null)
            {
                throw new ArgumentNullException(nameof(configureOptions));
            }

            Services.AddTransient<IPostConfigureOptions<TOptions>>(
                sp => new PostConfigureOptions<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5>(
                    Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    sp.GetRequiredService<TDep4>(),
                    sp.GetRequiredService<TDep5>(),
                    configureOptions));
            return this;
        }

        /// <summary>
        /// Register a validation action for an options type using a default failure message.
        /// </summary>
        /// <param name="validation">The validation function.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation)
            => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);

        /// <summary>
        /// Register a validation action for an options type.
        /// </summary>
        /// <param name="validation">The validation function.</param>
        /// <param name="failureMessage">The failure message to use when validation fails.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate(Func<TOptions, bool> validation, string failureMessage)
        {
            if (validation == null)
            {
                throw new ArgumentNullException(nameof(validation));
            }

            Services.AddSingleton<IValidateOptions<TOptions>>(new ValidateOptions<TOptions>(Name, validation, failureMessage));
            return this;
        }

        /// <summary>
        /// Register a validation action for an options type using a default failure message.
        /// </summary>
        /// <typeparam name="TDep">The dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep>(Func<TOptions, TDep, bool> validation)
            => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);

        /// <summary>
        /// Register a validation action for an options type.
        /// </summary>
        /// <typeparam name="TDep">The dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <param name="failureMessage">The failure message to use when validation fails.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep>(Func<TOptions, TDep, bool> validation, string failureMessage)
        {
            if (validation == null)
            {
                throw new ArgumentNullException(nameof(validation));
            }

            Services.AddTransient<IValidateOptions<TOptions>>(sp =>
                new ValidateOptions<TOptions, TDep>(Name, sp.GetRequiredService<TDep>(), validation, failureMessage));
            return this;
        }

        /// <summary>
        /// Register a validation action for an options type using a default failure message.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2>(Func<TOptions, TDep1, TDep2, bool> validation)
            => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);

        /// <summary>
        /// Register a validation action for an options type.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <param name="failureMessage">The failure message to use when validation fails.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2>(Func<TOptions, TDep1, TDep2, bool> validation, string failureMessage)
        {
            if (validation == null)
            {
                throw new ArgumentNullException(nameof(validation));
            }

            Services.AddTransient<IValidateOptions<TOptions>>(sp =>
                new ValidateOptions<TOptions, TDep1, TDep2>(Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    validation,
                    failureMessage));
            return this;
        }

        /// <summary>
        /// Register a validation action for an options type using a default failure message.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3>(Func<TOptions, TDep1, TDep2, TDep3, bool> validation)
            => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);

        /// <summary>
        /// Register a validation action for an options type.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <param name="failureMessage">The failure message to use when validation fails.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3>(Func<TOptions, TDep1, TDep2, TDep3, bool> validation, string failureMessage)
        {
            if (validation == null)
            {
                throw new ArgumentNullException(nameof(validation));
            }

            Services.AddTransient<IValidateOptions<TOptions>>(sp =>
                new ValidateOptions<TOptions, TDep1, TDep2, TDep3>(Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    validation,
                    failureMessage));
            return this;
        }

        /// <summary>
        /// Register a validation action for an options type using a default failure message.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3, TDep4>(Func<TOptions, TDep1, TDep2, TDep3, TDep4, bool> validation)
            => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);

        /// <summary>
        /// Register a validation action for an options type.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <param name="failureMessage">The failure message to use when validation fails.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3, TDep4>(Func<TOptions, TDep1, TDep2, TDep3, TDep4, bool> validation, string failureMessage)
        {
            if (validation == null)
            {
                throw new ArgumentNullException(nameof(validation));
            }

            Services.AddTransient<IValidateOptions<TOptions>>(sp =>
                new ValidateOptions<TOptions, TDep1, TDep2, TDep3, TDep4>(Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    sp.GetRequiredService<TDep4>(),
                    validation,
                    failureMessage));
            return this;
        }

        /// <summary>
        /// Register a validation action for an options type using a default failure message.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep5">The fifth dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3, TDep4, TDep5>(Func<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5, bool> validation)
            => Validate(validation: validation, failureMessage: DefaultValidationFailureMessage);

        /// <summary>
        /// Register a validation action for an options type.
        /// </summary>
        /// <typeparam name="TDep1">The first dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep2">The second dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep3">The third dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep4">The fourth dependency used by the validation function.</typeparam>
        /// <typeparam name="TDep5">The fifth dependency used by the validation function.</typeparam>
        /// <param name="validation">The validation function.</param>
        /// <param name="failureMessage">The failure message to use when validation fails.</param>
        /// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
        public virtual OptionsBuilder<TOptions> Validate<TDep1, TDep2, TDep3, TDep4, TDep5>(Func<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5, bool> validation, string failureMessage)
        {
            if (validation == null)
            {
                throw new ArgumentNullException(nameof(validation));
            }

            Services.AddTransient<IValidateOptions<TOptions>>(sp =>
                new ValidateOptions<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5>(Name,
                    sp.GetRequiredService<TDep1>(),
                    sp.GetRequiredService<TDep2>(),
                    sp.GetRequiredService<TDep3>(),
                    sp.GetRequiredService<TDep4>(),
                    sp.GetRequiredService<TDep5>(),
                    validation,
                    failureMessage));
            return this;
        }
    }
}

我们重点来看其中的一个方法，如下所示：

/// <summary>
/// Registers an action used to configure a particular type of options.
/// Note: These are run before all <seealso cref="PostConfigure(Action{TOptions})"/>.
/// </summary>
/// <param name="configureOptions">The action used to configure the options.</param>
/// <returns>The current <see cref="OptionsBuilder{TOptions}"/>.</returns>
public virtual OptionsBuilder<TOptions> Configure(Action<TOptions> configureOptions)
{
    if (configureOptions == null)
    {
        throw new ArgumentNullException(nameof(configureOptions));
    }

    Services.AddSingleton<IConfigureOptions<TOptions>>(new ConfigureNamedOptions<TOptions>(Name, configureOptions));
    return this;
}

可以发现其内部实现是和Configure方法一样的。

最后还有一种比较酷的用法，就是在调用Configure方法时并没有传递Action<TOptions>，而是直接传递了一个IConfiguration，如下所示：

services.Configure<AppSettingsOptions>(Configuration);
services.Configure<OtherConfig>(Configuration.GetSection("OtherConfig"));
services.Configure<OtherConfig>("FromConfiguration", Configuration.GetSection("OtherConfig"));

其实这是因为框架在内部帮我们转化了一下，最终传递的还是一个Action<TOptions>，下面我们就重点来看一下这个过程：

我们将光标移动到对应的 Configure 然后按 F12 转到定义，如下所示： 

可以发现此 Configure 是个扩展方法，位于 OptionsConfigurationServiceCollectionExtensions 类中，我们找到 OptionsConfigurationServiceCollectionExtensions 类的源码如下： 

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Options;

namespace Microsoft.Extensions.DependencyInjection
{
    /// <summary>
    /// Extension methods for adding configuration related options services to the DI container.
    /// </summary>
    public static class OptionsConfigurationServiceCollectionExtensions
    {
        /// <summary>
        /// Registers a configuration instance which TOptions will bind against.
        /// </summary>
        /// <typeparam name="TOptions">The type of options being configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="config">The configuration being bound.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection Configure<TOptions>(this IServiceCollection services, IConfiguration config) where TOptions : class
            => services.Configure<TOptions>(Options.Options.DefaultName, config);

        /// <summary>
        /// Registers a configuration instance which TOptions will bind against.
        /// </summary>
        /// <typeparam name="TOptions">The type of options being configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="name">The name of the options instance.</param>
        /// <param name="config">The configuration being bound.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, IConfiguration config) where TOptions : class
            => services.Configure<TOptions>(name, config, _ => { });

        /// <summary>
        /// Registers a configuration instance which TOptions will bind against.
        /// </summary>
        /// <typeparam name="TOptions">The type of options being configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="config">The configuration being bound.</param>
        /// <param name="configureBinder">Used to configure the <see cref="BinderOptions"/>.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection Configure<TOptions>(this IServiceCollection services, IConfiguration config, Action<BinderOptions> configureBinder)
            where TOptions : class
            => services.Configure<TOptions>(Options.Options.DefaultName, config, configureBinder);

        /// <summary>
        /// Registers a configuration instance which TOptions will bind against.
        /// </summary>
        /// <typeparam name="TOptions">The type of options being configured.</typeparam>
        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
        /// <param name="name">The name of the options instance.</param>
        /// <param name="config">The configuration being bound.</param>
        /// <param name="configureBinder">Used to configure the <see cref="BinderOptions"/>.</param>
        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
        public static IServiceCollection Configure<TOptions>(this IServiceCollection services, string name, IConfiguration config, Action<BinderOptions> configureBinder)
            where TOptions : class
        {
            if (services == null)
            {
                throw new ArgumentNullException(nameof(services));
            }

            if (config == null)
            {
                throw new ArgumentNullException(nameof(config));
            }

            services.AddOptions();
            services.AddSingleton<IOptionsChangeTokenSource<TOptions>>(new ConfigurationChangeTokenSource<TOptions>(name, config));
            return services.AddSingleton<IConfigureOptions<TOptions>>(new NamedConfigureFromConfigurationOptions<TOptions>(name, config, configureBinder));
        }
    }
}

从此处我们可以看出最终它会将 new NamedConfigureFromConfigurationOptions<TOptions>(name, config, configureBinder) 注册给 IConfigureOptions<TOptions> ，我们找到 NamedConfigureFromConfigurationOptions 类的源码，如下：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using Microsoft.Extensions.Configuration;

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Configures an option instance by using <see cref="ConfigurationBinder.Bind(IConfiguration, object)"/> against an <see cref="IConfiguration"/>.
    /// </summary>
    /// <typeparam name="TOptions">The type of options to bind.</typeparam>
    public class NamedConfigureFromConfigurationOptions<TOptions> : ConfigureNamedOptions<TOptions>
        where TOptions : class
    {
        /// <summary>
        /// Constructor that takes the <see cref="IConfiguration"/> instance to bind against.
        /// </summary>
        /// <param name="name">The name of the options instance.</param>
        /// <param name="config">The <see cref="IConfiguration"/> instance.</param>
        public NamedConfigureFromConfigurationOptions(string name, IConfiguration config)
            : this(name, config, _ => { })
        { }

        /// <summary>
        /// Constructor that takes the <see cref="IConfiguration"/> instance to bind against.
        /// </summary>
        /// <param name="name">The name of the options instance.</param>
        /// <param name="config">The <see cref="IConfiguration"/> instance.</param>
        /// <param name="configureBinder">Used to configure the <see cref="BinderOptions"/>.</param>
        public NamedConfigureFromConfigurationOptions(string name, IConfiguration config, Action<BinderOptions> configureBinder)
            : base(name, options => config.Bind(options, configureBinder))
        {
            if (config == null)
            {
                throw new ArgumentNullException(nameof(config));
            }
        }
    }
}

从中我们可以发现其实 NamedConfigureFromConfigurationOptions<TOptions> 类它是继承自 ConfigureNamedOptions<TOptions> 类的，我们继续找到 ConfigureNamedOptions<TOptions> 类的源码，如下：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type being configured.</typeparam>
    public class ConfigureNamedOptions<TOptions> : IConfigureNamedOptions<TOptions> where TOptions : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name">The name of the options.</param>
        /// <param name="action">The action to register.</param>
        public ConfigureNamedOptions(string name, Action<TOptions> action)
        {
            Name = name;
            Action = action;
        }

        /// <summary>
        /// The options name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The configuration action.
        /// </summary>
        public Action<TOptions> Action { get; }

        /// <summary>
        /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
        /// </summary>
        /// <param name="name">The name of the options instance being configured.</param>
        /// <param name="options">The options instance to configure.</param>
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options);
            }
        }

        /// <summary>
        /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
        /// </summary>
        /// <param name="options">The options instance to configure.</param>
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }

    /// <summary>
    /// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type being configured.</typeparam>
    /// <typeparam name="TDep">Dependency type.</typeparam>
    public class ConfigureNamedOptions<TOptions, TDep> : IConfigureNamedOptions<TOptions>
        where TOptions : class
        where TDep : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name">The name of the options.</param>
        /// <param name="dependency">A dependency.</param>
        /// <param name="action">The action to register.</param>
        public ConfigureNamedOptions(string name, TDep dependency, Action<TOptions, TDep> action)
        {
            Name = name;
            Action = action;
            Dependency = dependency;
        }

        /// <summary>
        /// The options name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The configuration action.
        /// </summary>
        public Action<TOptions, TDep> Action { get; }

        /// <summary>
        /// The dependency.
        /// </summary>
        public TDep Dependency { get; }

        /// <summary>
        /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
        /// </summary>
        /// <param name="name">The name of the options instance being configured.</param>
        /// <param name="options">The options instance to configure.</param>
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options, Dependency);
            }
        }

        /// <summary>
        /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
        /// </summary>
        /// <param name="options">The options instance to configure.</param>
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }

    /// <summary>
    /// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type being configured.</typeparam>
    /// <typeparam name="TDep1">First dependency type.</typeparam>
    /// <typeparam name="TDep2">Second dependency type.</typeparam>
    public class ConfigureNamedOptions<TOptions, TDep1, TDep2> : IConfigureNamedOptions<TOptions>
        where TOptions : class
        where TDep1 : class
        where TDep2 : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name">The name of the options.</param>
        /// <param name="dependency">A dependency.</param>
        /// <param name="dependency2">A second dependency.</param>
        /// <param name="action">The action to register.</param>
        public ConfigureNamedOptions(string name, TDep1 dependency, TDep2 dependency2, Action<TOptions, TDep1, TDep2> action)
        {
            Name = name;
            Action = action;
            Dependency1 = dependency;
            Dependency2 = dependency2;
        }

        /// <summary>
        /// The options name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The configuration action.
        /// </summary>
        public Action<TOptions, TDep1, TDep2> Action { get; }

        /// <summary>
        /// The first dependency.
        /// </summary>
        public TDep1 Dependency1 { get; }

        /// <summary>
        /// The second dependency.
        /// </summary>
        public TDep2 Dependency2 { get; }

        /// <summary>
        /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
        /// </summary>
        /// <param name="name">The name of the options instance being configured.</param>
        /// <param name="options">The options instance to configure.</param>
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options, Dependency1, Dependency2);
            }
        }

        /// <summary>
        /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
        /// </summary>
        /// <param name="options">The options instance to configure.</param>
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }

    /// <summary>
    /// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type being configured.</typeparam>
    /// <typeparam name="TDep1">First dependency type.</typeparam>
    /// <typeparam name="TDep2">Second dependency type.</typeparam>
    /// <typeparam name="TDep3">Third dependency type.</typeparam>
    public class ConfigureNamedOptions<TOptions, TDep1, TDep2, TDep3> : IConfigureNamedOptions<TOptions>
        where TOptions : class
        where TDep1 : class
        where TDep2 : class
        where TDep3 : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name">The name of the options.</param>
        /// <param name="dependency">A dependency.</param>
        /// <param name="dependency2">A second dependency.</param>
        /// <param name="dependency3">A third dependency.</param>
        /// <param name="action">The action to register.</param>
        public ConfigureNamedOptions(string name, TDep1 dependency, TDep2 dependency2, TDep3 dependency3, Action<TOptions, TDep1, TDep2, TDep3> action)
        {
            Name = name;
            Action = action;
            Dependency1 = dependency;
            Dependency2 = dependency2;
            Dependency3 = dependency3;
        }

        /// <summary>
        /// The options name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The configuration action.
        /// </summary>
        public Action<TOptions, TDep1, TDep2, TDep3> Action { get; }

        /// <summary>
        /// The first dependency.
        /// </summary>
        public TDep1 Dependency1 { get; }

        /// <summary>
        /// The second dependency.
        /// </summary>
        public TDep2 Dependency2 { get; }

        /// <summary>
        /// The third dependency.
        /// </summary>
        public TDep3 Dependency3 { get; }

        /// <summary>
        /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
        /// </summary>
        /// <param name="name">The name of the options instance being configured.</param>
        /// <param name="options">The options instance to configure.</param>
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options, Dependency1, Dependency2, Dependency3);
            }
        }

        /// <summary>
        /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
        /// </summary>
        /// <param name="options">The options instance to configure.</param>
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }

    /// <summary>
    /// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type being configured.</typeparam>
    /// <typeparam name="TDep1">First dependency type.</typeparam>
    /// <typeparam name="TDep2">Second dependency type.</typeparam>
    /// <typeparam name="TDep3">Third dependency type.</typeparam>
    /// <typeparam name="TDep4">Fourth dependency type.</typeparam>
    public class ConfigureNamedOptions<TOptions, TDep1, TDep2, TDep3, TDep4> : IConfigureNamedOptions<TOptions>
        where TOptions : class
        where TDep1 : class
        where TDep2 : class
        where TDep3 : class
        where TDep4 : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name">The name of the options.</param>
        /// <param name="dependency1">A dependency.</param>
        /// <param name="dependency2">A second dependency.</param>
        /// <param name="dependency3">A third dependency.</param>
        /// <param name="dependency4">A fourth dependency.</param>
        /// <param name="action">The action to register.</param>
        public ConfigureNamedOptions(string name, TDep1 dependency1, TDep2 dependency2, TDep3 dependency3, TDep4 dependency4, Action<TOptions, TDep1, TDep2, TDep3, TDep4> action)
        {
            Name = name;
            Action = action;
            Dependency1 = dependency1;
            Dependency2 = dependency2;
            Dependency3 = dependency3;
            Dependency4 = dependency4;
        }

        /// <summary>
        /// The options name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The configuration action.
        /// </summary>
        public Action<TOptions, TDep1, TDep2, TDep3, TDep4> Action { get; }

        /// <summary>
        /// The first dependency.
        /// </summary>
        public TDep1 Dependency1 { get; }

        /// <summary>
        /// The second dependency.
        /// </summary>
        public TDep2 Dependency2 { get; }

        /// <summary>
        /// The third dependency.
        /// </summary>
        public TDep3 Dependency3 { get; }

        /// <summary>
        /// The fourth dependency.
        /// </summary>
        public TDep4 Dependency4 { get; }

        /// <summary>
        /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
        /// </summary>
        /// <param name="name">The name of the options instance being configured.</param>
        /// <param name="options">The options instance to configure.</param>
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options, Dependency1, Dependency2, Dependency3, Dependency4);
            }
        }

        /// <summary>
        /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
        /// </summary>
        /// <param name="options">The options instance to configure.</param>
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }

    /// <summary>
    /// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type being configured.</typeparam>
    /// <typeparam name="TDep1">First dependency type.</typeparam>
    /// <typeparam name="TDep2">Second dependency type.</typeparam>
    /// <typeparam name="TDep3">Third dependency type.</typeparam>
    /// <typeparam name="TDep4">Fourth dependency type.</typeparam>
    /// <typeparam name="TDep5">Fifth dependency type.</typeparam>
    public class ConfigureNamedOptions<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5> : IConfigureNamedOptions<TOptions>
        where TOptions : class
        where TDep1 : class
        where TDep2 : class
        where TDep3 : class
        where TDep4 : class
        where TDep5 : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="name">The name of the options.</param>
        /// <param name="dependency1">A dependency.</param>
        /// <param name="dependency2">A second dependency.</param>
        /// <param name="dependency3">A third dependency.</param>
        /// <param name="dependency4">A fourth dependency.</param>
        /// <param name="dependency5">A fifth dependency.</param>
        /// <param name="action">The action to register.</param>
        public ConfigureNamedOptions(string name, TDep1 dependency1, TDep2 dependency2, TDep3 dependency3, TDep4 dependency4, TDep5 dependency5, Action<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5> action)
        {
            Name = name;
            Action = action;
            Dependency1 = dependency1;
            Dependency2 = dependency2;
            Dependency3 = dependency3;
            Dependency4 = dependency4;
            Dependency5 = dependency5;
        }

        /// <summary>
        /// The options name.
        /// </summary>
        public string Name { get; }

        /// <summary>
        /// The configuration action.
        /// </summary>
        public Action<TOptions, TDep1, TDep2, TDep3, TDep4, TDep5> Action { get; }

        /// <summary>
        /// The first dependency.
        /// </summary>
        public TDep1 Dependency1 { get; }

        /// <summary>
        /// The second dependency.
        /// </summary>
        public TDep2 Dependency2 { get; }

        /// <summary>
        /// The third dependency.
        /// </summary>
        public TDep3 Dependency3 { get; }

        /// <summary>
        /// The fourth dependency.
        /// </summary>
        public TDep4 Dependency4 { get; }

        /// <summary>
        /// The fifth dependency.
        /// </summary>
        public TDep5 Dependency5 { get; }

        /// <summary>
        /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
        /// </summary>
        /// <param name="name">The name of the options instance being configured.</param>
        /// <param name="options">The options instance to configure.</param>
        public virtual void Configure(string name, TOptions options)
        {
            if (options == null)
            {
                throw new ArgumentNullException(nameof(options));
            }

            // Null name is used to configure all named options.
            if (Name == null || name == Name)
            {
                Action?.Invoke(options, Dependency1, Dependency2, Dependency3, Dependency4, Dependency5);
            }
        }

        /// <summary>
        /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
        /// </summary>
        /// <param name="options">The options instance to configure.</param>
        public void Configure(TOptions options) => Configure(Options.DefaultName, options);
    }
}

其中我们重点来看下面的这部分：

/// <summary>
/// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
/// </summary>
/// <typeparam name="TOptions">Options type being configured.</typeparam>
public class ConfigureNamedOptions<TOptions> : IConfigureNamedOptions<TOptions> where TOptions : class
{
    /// <summary>
    /// Constructor.
    /// </summary>
    /// <param name="name">The name of the options.</param>
    /// <param name="action">The action to register.</param>
    public ConfigureNamedOptions(string name, Action<TOptions> action)
    {
        Name = name;
        Action = action;
    }

    /// <summary>
    /// The options name.
    /// </summary>
    public string Name { get; }

    /// <summary>
    /// The configuration action.
    /// </summary>
    public Action<TOptions> Action { get; }

    /// <summary>
    /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
    /// </summary>
    /// <param name="name">The name of the options instance being configured.</param>
    /// <param name="options">The options instance to configure.</param>
    public virtual void Configure(string name, TOptions options)
    {
        if (options == null)
        {
            throw new ArgumentNullException(nameof(options));
        }

        // Null name is used to configure all named options.
        if (Name == null || name == Name)
        {
            Action?.Invoke(options);
        }
    }

    /// <summary>
    /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
    /// </summary>
    /// <param name="options">The options instance to configure.</param>
    public void Configure(TOptions options) => Configure(Options.DefaultName, options);
}

结合 NamedConfigureFromConfigurationOptions<TOptions> 和 ConfigureNamedOptions<TOptions> 这两个类的源码我们可以发现：

1、 调用 services.Configure<AppSettingsOptions>(Configuration) 方法时框架在内部帮我们转化了一下，最终传递的是 “options => config.Bind(options, configureBinder)” 。

2、 调用 Configure(string name, TOptions options) 方法时会把Name值为null的Action<TOptions>应用于所有TOptions实例。

我们找到 config.Bind(options, configureBinder) 这个方法，它是个扩展方法，位于 ConfigurationBinder 静态类中，如下：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Reflection;
using Microsoft.Extensions.Configuration.Binder;

namespace Microsoft.Extensions.Configuration
{
    /// <summary>
    /// Static helper class that allows binding strongly typed objects to configuration values.
    /// </summary>
    public static class ConfigurationBinder
    {
        /// <summary>
        /// Attempts to bind the configuration instance to a new instance of type T.
        /// If this configuration section has a value, that will be used.
        /// Otherwise binding by matching property names against configuration keys recursively.
        /// </summary>
        /// <typeparam name="T">The type of the new instance to bind.</typeparam>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <returns>The new instance of T if successful, default(T) otherwise.</returns>
        public static T Get<T>(this IConfiguration configuration)
            => configuration.Get<T>(_ => { });

        /// <summary>
        /// Attempts to bind the configuration instance to a new instance of type T.
        /// If this configuration section has a value, that will be used.
        /// Otherwise binding by matching property names against configuration keys recursively.
        /// </summary>
        /// <typeparam name="T">The type of the new instance to bind.</typeparam>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <param name="configureOptions">Configures the binder options.</param>
        /// <returns>The new instance of T if successful, default(T) otherwise.</returns>
        public static T Get<T>(this IConfiguration configuration, Action<BinderOptions> configureOptions)
        {
            if (configuration == null)
            {
                throw new ArgumentNullException(nameof(configuration));
            }

            var result = configuration.Get(typeof(T), configureOptions);
            if (result == null)
            {
                return default(T);
            }
            return (T)result;
        }

        /// <summary>
        /// Attempts to bind the configuration instance to a new instance of type T.
        /// If this configuration section has a value, that will be used.
        /// Otherwise binding by matching property names against configuration keys recursively.
        /// </summary>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <param name="type">The type of the new instance to bind.</param>
        /// <returns>The new instance if successful, null otherwise.</returns>
        public static object Get(this IConfiguration configuration, Type type)
            => configuration.Get(type, _ => { });

        /// <summary>
        /// Attempts to bind the configuration instance to a new instance of type T.
        /// If this configuration section has a value, that will be used.
        /// Otherwise binding by matching property names against configuration keys recursively.
        /// </summary>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <param name="type">The type of the new instance to bind.</param>
        /// <param name="configureOptions">Configures the binder options.</param>
        /// <returns>The new instance if successful, null otherwise.</returns>
        public static object Get(this IConfiguration configuration, Type type, Action<BinderOptions> configureOptions)
        {
            if (configuration == null)
            {
                throw new ArgumentNullException(nameof(configuration));
            }

            var options = new BinderOptions();
            configureOptions?.Invoke(options);
            return BindInstance(type, instance: null, config: configuration, options: options);
        }

        /// <summary>
        /// Attempts to bind the given object instance to the configuration section specified by the key by matching property names against configuration keys recursively.
        /// </summary>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <param name="key">The key of the configuration section to bind.</param>
        /// <param name="instance">The object to bind.</param>
        public static void Bind(this IConfiguration configuration, string key, object instance)
            => configuration.GetSection(key).Bind(instance);

        /// <summary>
        /// Attempts to bind the given object instance to configuration values by matching property names against configuration keys recursively.
        /// </summary>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <param name="instance">The object to bind.</param>
        public static void Bind(this IConfiguration configuration, object instance)
            => configuration.Bind(instance, o => { });

        /// <summary>
        /// Attempts to bind the given object instance to configuration values by matching property names against configuration keys recursively.
        /// </summary>
        /// <param name="configuration">The configuration instance to bind.</param>
        /// <param name="instance">The object to bind.</param>
        /// <param name="configureOptions">Configures the binder options.</param>
        public static void Bind(this IConfiguration configuration, object instance, Action<BinderOptions> configureOptions)
        {
            if (configuration == null)
            {
                throw new ArgumentNullException(nameof(configuration));
            }

            if (instance != null)
            {
                var options = new BinderOptions();
                configureOptions?.Invoke(options);
                BindInstance(instance.GetType(), instance, configuration, options);
            }
        }

        /// <summary>
        /// Extracts the value with the specified key and converts it to type T.
        /// </summary>
        /// <typeparam name="T">The type to convert the value to.</typeparam>
        /// <param name="configuration">The configuration.</param>
        /// <param name="key">The key of the configuration section's value to convert.</param>
        /// <returns>The converted value.</returns>
        public static T GetValue<T>(this IConfiguration configuration, string key)
        {
            return GetValue(configuration, key, default(T));
        }

        /// <summary>
        /// Extracts the value with the specified key and converts it to type T.
        /// </summary>
        /// <typeparam name="T">The type to convert the value to.</typeparam>
        /// <param name="configuration">The configuration.</param>
        /// <param name="key">The key of the configuration section's value to convert.</param>
        /// <param name="defaultValue">The default value to use if no value is found.</param>
        /// <returns>The converted value.</returns>
        public static T GetValue<T>(this IConfiguration configuration, string key, T defaultValue)
        {
            return (T)GetValue(configuration, typeof(T), key, defaultValue);
        }

        /// <summary>
        /// Extracts the value with the specified key and converts it to the specified type.
        /// </summary>
        /// <param name="configuration">The configuration.</param>
        /// <param name="type">The type to convert the value to.</param>
        /// <param name="key">The key of the configuration section's value to convert.</param>
        /// <returns>The converted value.</returns>
        public static object GetValue(this IConfiguration configuration, Type type, string key)
        {
            return GetValue(configuration, type, key, defaultValue: null);
        }

        /// <summary>
        /// Extracts the value with the specified key and converts it to the specified type.
        /// </summary>
        /// <param name="configuration">The configuration.</param>
        /// <param name="type">The type to convert the value to.</param>
        /// <param name="key">The key of the configuration section's value to convert.</param>
        /// <param name="defaultValue">The default value to use if no value is found.</param>
        /// <returns>The converted value.</returns>
        public static object GetValue(this IConfiguration configuration, Type type, string key, object defaultValue)
        {
            var section = configuration.GetSection(key);
            var value = section.Value;
            if (value != null)
            {
                return ConvertValue(type, value, section.Path);
            }
            return defaultValue;
        }

        private static void BindNonScalar(this IConfiguration configuration, object instance, BinderOptions options)
        {
            if (instance != null)
            {
                foreach (var property in GetAllProperties(instance.GetType().GetTypeInfo()))
                {
                    BindProperty(property, instance, configuration, options);
                }
            }
        }

        private static void BindProperty(PropertyInfo property, object instance, IConfiguration config, BinderOptions options)
        {
            // We don't support set only, non public, or indexer properties
            if (property.GetMethod == null ||
                (!options.BindNonPublicProperties && !property.GetMethod.IsPublic) ||
                property.GetMethod.GetParameters().Length > 0)
            {
                return;
            }

            var propertyValue = property.GetValue(instance);
            var hasSetter = property.SetMethod != null && (property.SetMethod.IsPublic || options.BindNonPublicProperties);

            if (propertyValue == null && !hasSetter)
            {
                // Property doesn't have a value and we cannot set it so there is no
                // point in going further down the graph
                return;
            }

            propertyValue = BindInstance(property.PropertyType, propertyValue, config.GetSection(property.Name), options);

            if (propertyValue != null && hasSetter)
            {
                property.SetValue(instance, propertyValue);
            }
        }

        private static object BindToCollection(TypeInfo typeInfo, IConfiguration config, BinderOptions options)
        {
            var type = typeof(List<>).MakeGenericType(typeInfo.GenericTypeArguments[0]);
            var instance = Activator.CreateInstance(type);
            BindCollection(instance, type, config, options);
            return instance;
        }

        // Try to create an array/dictionary instance to back various collection interfaces
        private static object AttemptBindToCollectionInterfaces(Type type, IConfiguration config, BinderOptions options)
        {
            var typeInfo = type.GetTypeInfo();

            if (!typeInfo.IsInterface)
            {
                return null;
            }

            var collectionInterface = FindOpenGenericInterface(typeof(IReadOnlyList<>), type);
            if (collectionInterface != null)
            {
                // IEnumerable<T> is guaranteed to have exactly one parameter
                return BindToCollection(typeInfo, config, options);
            }

            collectionInterface = FindOpenGenericInterface(typeof(IReadOnlyDictionary<,>), type);
            if (collectionInterface != null)
            {
                var dictionaryType = typeof(Dictionary<,>).MakeGenericType(typeInfo.GenericTypeArguments[0], typeInfo.GenericTypeArguments[1]);
                var instance = Activator.CreateInstance(dictionaryType);
                BindDictionary(instance, dictionaryType, config, options);
                return instance;
            }

            collectionInterface = FindOpenGenericInterface(typeof(IDictionary<,>), type);
            if (collectionInterface != null)
            {
                var instance = Activator.CreateInstance(typeof(Dictionary<,>).MakeGenericType(typeInfo.GenericTypeArguments[0], typeInfo.GenericTypeArguments[1]));
                BindDictionary(instance, collectionInterface, config, options);
                return instance;
            }

            collectionInterface = FindOpenGenericInterface(typeof(IReadOnlyCollection<>), type);
            if (collectionInterface != null)
            {
                // IReadOnlyCollection<T> is guaranteed to have exactly one parameter
                return BindToCollection(typeInfo, config, options);
            }

            collectionInterface = FindOpenGenericInterface(typeof(ICollection<>), type);
            if (collectionInterface != null)
            {
                // ICollection<T> is guaranteed to have exactly one parameter
                return BindToCollection(typeInfo, config, options);
            }

            collectionInterface = FindOpenGenericInterface(typeof(IEnumerable<>), type);
            if (collectionInterface != null)
            {
                // IEnumerable<T> is guaranteed to have exactly one parameter
                return BindToCollection(typeInfo, config, options);
            }

            return null;
        }

        private static object BindInstance(Type type, object instance, IConfiguration config, BinderOptions options)
        {
            // if binding IConfigurationSection, break early
            if (type == typeof(IConfigurationSection))
            {
                return config;
            }

            var section = config as IConfigurationSection;
            var configValue = section?.Value;
            object convertedValue;
            Exception error;
            if (configValue != null && TryConvertValue(type, configValue, section.Path, out convertedValue, out error))
            {
                if (error != null)
                {
                    throw error;
                }

                // Leaf nodes are always reinitialized
                return convertedValue;
            }

            if (config != null && config.GetChildren().Any())
            {
                // If we don't have an instance, try to create one
                if (instance == null)
                {
                    // We are already done if binding to a new collection instance worked
                    instance = AttemptBindToCollectionInterfaces(type, config, options);
                    if (instance != null)
                    {
                        return instance;
                    }

                    instance = CreateInstance(type);
                }

                // See if its a Dictionary
                var collectionInterface = FindOpenGenericInterface(typeof(IDictionary<,>), type);
                if (collectionInterface != null)
                {
                    BindDictionary(instance, collectionInterface, config, options);
                }
                else if (type.IsArray)
                {
                    instance = BindArray((Array)instance, config, options);
                }
                else
                {
                    // See if its an ICollection
                    collectionInterface = FindOpenGenericInterface(typeof(ICollection<>), type);
                    if (collectionInterface != null)
                    {
                        BindCollection(instance, collectionInterface, config, options);
                    }
                    // Something else
                    else
                    {
                        BindNonScalar(config, instance, options);
                    }
                }
            }

            return instance;
        }

        private static object CreateInstance(Type type)
        {
            var typeInfo = type.GetTypeInfo();

            if (typeInfo.IsInterface || typeInfo.IsAbstract)
            {
                throw new InvalidOperationException(Resources.FormatError_CannotActivateAbstractOrInterface(type));
            }

            if (type.IsArray)
            {
                if (typeInfo.GetArrayRank() > 1)
                {
                    throw new InvalidOperationException(Resources.FormatError_UnsupportedMultidimensionalArray(type));
                }

                return Array.CreateInstance(typeInfo.GetElementType(), 0);
            }

            var hasDefaultConstructor = typeInfo.DeclaredConstructors.Any(ctor => ctor.IsPublic && ctor.GetParameters().Length == 0);
            if (!hasDefaultConstructor)
            {
                throw new InvalidOperationException(Resources.FormatError_MissingParameterlessConstructor(type));
            }

            try
            {
                return Activator.CreateInstance(type);
            }
            catch (Exception ex)
            {
                throw new InvalidOperationException(Resources.FormatError_FailedToActivate(type), ex);
            }
        }

        private static void BindDictionary(object dictionary, Type dictionaryType, IConfiguration config, BinderOptions options)
        {
            var typeInfo = dictionaryType.GetTypeInfo();

            // IDictionary<K,V> is guaranteed to have exactly two parameters
            var keyType = typeInfo.GenericTypeArguments[0];
            var valueType = typeInfo.GenericTypeArguments[1];
            var keyTypeIsEnum = keyType.GetTypeInfo().IsEnum;

            if (keyType != typeof(string) && !keyTypeIsEnum)
            {
                // We only support string and enum keys
                return;
            }

            var setter = typeInfo.GetDeclaredProperty("Item");
            foreach (var child in config.GetChildren())
            {
                var item = BindInstance(
                    type: valueType,
                    instance: null,
                    config: child,
                    options: options);
                if (item != null)
                {
                    if (keyType == typeof(string))
                    {
                        var key = child.Key;
                        setter.SetValue(dictionary, item, new object[] { key });
                    }
                    else if (keyTypeIsEnum)
                    {
                        var key = Enum.Parse(keyType, child.Key);
                        setter.SetValue(dictionary, item, new object[] { key });
                    }
                }
            }
        }

        private static void BindCollection(object collection, Type collectionType, IConfiguration config, BinderOptions options)
        {
            var typeInfo = collectionType.GetTypeInfo();

            // ICollection<T> is guaranteed to have exactly one parameter
            var itemType = typeInfo.GenericTypeArguments[0];
            var addMethod = typeInfo.GetDeclaredMethod("Add");

            foreach (var section in config.GetChildren())
            {
                try
                {
                    var item = BindInstance(
                        type: itemType,
                        instance: null,
                        config: section,
                        options: options);
                    if (item != null)
                    {
                        addMethod.Invoke(collection, new[] { item });
                    }
                }
                catch
                {
                }
            }
        }

        private static Array BindArray(Array source, IConfiguration config, BinderOptions options)
        {
            var children = config.GetChildren().ToArray();
            var arrayLength = source.Length;
            var elementType = source.GetType().GetElementType();
            var newArray = Array.CreateInstance(elementType, arrayLength + children.Length);

            // binding to array has to preserve already initialized arrays with values
            if (arrayLength > 0)
            {
                Array.Copy(source, newArray, arrayLength);
            }

            for (int i = 0; i < children.Length; i++)
            {
                try
                {
                    var item = BindInstance(
                        type: elementType,
                        instance: null,
                        config: children[i],
                        options: options);
                    if (item != null)
                    {
                        newArray.SetValue(item, arrayLength + i);
                    }
                }
                catch
                {
                }
            }

            return newArray;
        }

        private static bool TryConvertValue(Type type, string value, string path, out object result, out Exception error)
        {
            error = null;
            result = null;
            if (type == typeof(object))
            {
                result = value;
                return true;
            }

            if (type.GetTypeInfo().IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))
            {
                if (string.IsNullOrEmpty(value))
                {
                    return true;
                }
                return TryConvertValue(Nullable.GetUnderlyingType(type), value, path, out result, out error);
            }

            var converter = TypeDescriptor.GetConverter(type);
            if (converter.CanConvertFrom(typeof(string)))
            {
                try
                {
                    result = converter.ConvertFromInvariantString(value);
                }
                catch (Exception ex)
                {
                    error = new InvalidOperationException(Resources.FormatError_FailedBinding(path, type), ex);
                }
                return true;
            }

            return false;
        }

        private static object ConvertValue(Type type, string value, string path)
        {
            object result;
            Exception error;
            TryConvertValue(type, value, path, out result, out error);
            if (error != null)
            {
                throw error;
            }
            return result;
        }

        private static Type FindOpenGenericInterface(Type expected, Type actual)
        {
            var actualTypeInfo = actual.GetTypeInfo();
            if(actualTypeInfo.IsGenericType &&
                actual.GetGenericTypeDefinition() == expected)
            {
                return actual;
            }

            var interfaces = actualTypeInfo.ImplementedInterfaces;
            foreach (var interfaceType in interfaces)
            {
                if (interfaceType.GetTypeInfo().IsGenericType &&
                    interfaceType.GetGenericTypeDefinition() == expected)
                {
                    return interfaceType;
                }
            }
            return null;
        }

        private static IEnumerable<PropertyInfo> GetAllProperties(TypeInfo type)
        {
            var allProperties = new List<PropertyInfo>();

            do
            {
                allProperties.AddRange(type.DeclaredProperties);
                type = type.BaseType.GetTypeInfo();
            }
            while (type != typeof(object).GetTypeInfo());

            return allProperties;
        }
    }
}

仔细阅读上面的源码你会发现，其实它是通过反射的方式为TOptions实例赋值的，而它的值则是通过IConfiguration方式获取的，如果通过IConfiguration方式没有获取到指定的值则不做任何处理还是保留原来的默认值。对于使用IConfiguration获取配置值的实现原理，这在上一篇我们已经详细的讲解过了，此处就不再做过多的介绍了。

从上文的分析中我们可以知道，不管是采用哪种绑定配置的方式其内部都会调用 services.AddOptions() 这个方法，该方法位于OptionsServiceCollectionExtensions静态类中，我们找到该方法，如下所示：

/// <summary>
/// Adds services required for using options.
/// </summary>
/// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
/// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
public static IServiceCollection AddOptions(this IServiceCollection services)
{
    if (services == null)
    {
        throw new ArgumentNullException(nameof(services));
    }

    services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptions<>), typeof(OptionsManager<>)));
    services.TryAdd(ServiceDescriptor.Scoped(typeof(IOptionsSnapshot<>), typeof(OptionsManager<>)));
    services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitor<>), typeof(OptionsMonitor<>)));
    services.TryAdd(ServiceDescriptor.Transient(typeof(IOptionsFactory<>), typeof(OptionsFactory<>)));
    services.TryAdd(ServiceDescriptor.Singleton(typeof(IOptionsMonitorCache<>), typeof(OptionsCache<>)));
    return services;
}

从中我们大概能猜出 IOptions<TOptions>、IOptionsMonitor<TOptions> 以及 IOptionsSnapshot<TOptions> 这三者的主要区别：

1、IOptions在注册到容器时是以单例的形式，这种方式数据全局唯一，不支持数据变化。

2、IOptionsSnapshot在注册到容器时是以Scoped的形式，这种方式单次请求数据是不变的，但是不同的请求数据有可能是不一样的，它能觉察到配置源的改变。

3、IOptionsMonitor在注册到容器时虽然也是以单例的形式，但是它多了一个IOptionsMonitorCache缓存，它也是能觉察到配置源的改变，一旦发生改变就会告知OptionsMonitor从缓存中移除相应的对象。

下面我们继续往下分析，首先找到 OptionsManager 类的源码，如下所示：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Implementation of <see cref="IOptions{TOptions}"/> and <see cref="IOptionsSnapshot{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type.</typeparam>
    public class OptionsManager<TOptions> : IOptions<TOptions>, IOptionsSnapshot<TOptions> where TOptions : class, new()
    {
        private readonly IOptionsFactory<TOptions> _factory;
        private readonly OptionsCache<TOptions> _cache = new OptionsCache<TOptions>(); // Note: this is a private cache

        /// <summary>
        /// Initializes a new instance with the specified options configurations.
        /// </summary>
        /// <param name="factory">The factory to use to create options.</param>
        public OptionsManager(IOptionsFactory<TOptions> factory)
        {
            _factory = factory;
        }

        /// <summary>
        /// The default configured <typeparamref name="TOptions"/> instance, equivalent to Get(Options.DefaultName).
        /// </summary>
        public TOptions Value
        {
            get
            {
                return Get(Options.DefaultName);
            }
        }

        /// <summary>
        /// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>.
        /// </summary>
        public virtual TOptions Get(string name)
        {
            name = name ?? Options.DefaultName;

            // Store the options in our instance cache
            return _cache.GetOrAdd(name, () => _factory.Create(name));
        }
    }
}

可以发现TOptions对象是通过IOptionsFactory工厂产生的，我们继续找到 OptionsFactory 类的源码，如下：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System.Collections.Generic;

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Implementation of <see cref="IOptionsFactory{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">The type of options being requested.</typeparam>
    public class OptionsFactory<TOptions> : IOptionsFactory<TOptions> where TOptions : class, new()
    {
        private readonly IEnumerable<IConfigureOptions<TOptions>> _setups;
        private readonly IEnumerable<IPostConfigureOptions<TOptions>> _postConfigures;
        private readonly IEnumerable<IValidateOptions<TOptions>> _validations;

        /// <summary>
        /// Initializes a new instance with the specified options configurations.
        /// </summary>
        /// <param name="setups">The configuration actions to run.</param>
        /// <param name="postConfigures">The initialization actions to run.</param>
        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures) : this(setups, postConfigures, validations: null)
        { }

        /// <summary>
        /// Initializes a new instance with the specified options configurations.
        /// </summary>
        /// <param name="setups">The configuration actions to run.</param>
        /// <param name="postConfigures">The initialization actions to run.</param>
        /// <param name="validations">The validations to run.</param>
        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IPostConfigureOptions<TOptions>> postConfigures, IEnumerable<IValidateOptions<TOptions>> validations)
        {
            _setups = setups;
            _postConfigures = postConfigures;
            _validations = validations;
        }

        /// <summary>
        /// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>.
        /// </summary>
        public TOptions Create(string name)
        {
            var options = new TOptions();
            foreach (var setup in _setups)
            {
                if (setup is IConfigureNamedOptions<TOptions> namedSetup)
                {
                    namedSetup.Configure(name, options);
                }
                else if (name == Options.DefaultName)
                {
                    setup.Configure(options);
                }
            }
            foreach (var post in _postConfigures)
            {
                post.PostConfigure(name, options);
            }

            if (_validations != null)
            {
                var failures = new List<string>();
                foreach (var validate in _validations)
                {
                    var result = validate.Validate(name, options);
                    if (result.Failed)
                    {
                        failures.AddRange(result.Failures);
                    }
                }
                if (failures.Count > 0)
                {
                    throw new OptionsValidationException(name, typeof(TOptions), failures);
                }
            }

            return options;
        }
    }
}

从此处我们可以看出，在调用 Create(string name) 方法时，首先它会去先创建一个 TOptions 对象，接着再遍历 _setups 集合去依次调用所有的 Configure 方法，最后再遍历 _postConfigures 集合去依次调用所有的 PostConfigure 方法。而从上文的分析中我们知道此时 _setups 集合中存放的是 ConfigureNamedOptions<TOptions> 类型的对象，_postConfigures 集合中存放的则是 PostConfigureOptions<TOptions> 类型的对象。我们分别找到这两个类的源码，如下所示：

/// <summary>
/// Implementation of <see cref="IConfigureNamedOptions{TOptions}"/>.
/// </summary>
/// <typeparam name="TOptions">Options type being configured.</typeparam>
public class ConfigureNamedOptions<TOptions> : IConfigureNamedOptions<TOptions> where TOptions : class
{
    /// <summary>
    /// Constructor.
    /// </summary>
    /// <param name="name">The name of the options.</param>
    /// <param name="action">The action to register.</param>
    public ConfigureNamedOptions(string name, Action<TOptions> action)
    {
        Name = name;
        Action = action;
    }

    /// <summary>
    /// The options name.
    /// </summary>
    public string Name { get; }

    /// <summary>
    /// The configuration action.
    /// </summary>
    public Action<TOptions> Action { get; }

    /// <summary>
    /// Invokes the registered configure <see cref="Action"/> if the <paramref name="name"/> matches.
    /// </summary>
    /// <param name="name">The name of the options instance being configured.</param>
    /// <param name="options">The options instance to configure.</param>
    public virtual void Configure(string name, TOptions options)
    {
        if (options == null)
        {
            throw new ArgumentNullException(nameof(options));
        }

        // Null name is used to configure all named options.
        if (Name == null || name == Name)
        {
            Action?.Invoke(options);
        }
    }

    /// <summary>
    /// Invoked to configure a <typeparamref name="TOptions"/> instance with the <see cref="Options.DefaultName"/>.
    /// </summary>
    /// <param name="options">The options instance to configure.</param>
    public void Configure(TOptions options) => Configure(Options.DefaultName, options);
}

/// <summary>
/// Implementation of <see cref="IPostConfigureOptions{TOptions}"/>.
/// </summary>
/// <typeparam name="TOptions">Options type being configured.</typeparam>
public class PostConfigureOptions<TOptions> : IPostConfigureOptions<TOptions> where TOptions : class
{
    /// <summary>
    /// Creates a new instance of <see cref="PostConfigureOptions{TOptions}"/>.
    /// </summary>
    /// <param name="name">The name of the options.</param>
    /// <param name="action">The action to register.</param>
    public PostConfigureOptions(string name, Action<TOptions> action)
    {
        Name = name;
        Action = action;
    }

    /// <summary>
    /// The options name.
    /// </summary>
    public string Name { get; }

    /// <summary>
    /// The initialization action.
    /// </summary>
    public Action<TOptions> Action { get; }

    /// <summary>
    /// Invokes the registered initialization <see cref="Action"/> if the <paramref name="name"/> matches.
    /// </summary>
    /// <param name="name">The name of the action to invoke.</param>
    /// <param name="options">The options to use in initialization.</param>
    public virtual void PostConfigure(string name, TOptions options)
    {
        if (options == null)
        {
            throw new ArgumentNullException(nameof(options));
        }

        // Null name is used to initialize all named options.
        if (Name == null || name == Name)
        {
            Action?.Invoke(options);
        }
    }
}

仔细阅读上面的源码我们就会发现最终它会把Name值为null的Action<TOptions>应用于所有的TOptions实例。

至此，我们整个流程就都串起来了，最后我们来看下 OptionsMonitor 类的源码，如下所示：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using Microsoft.Extensions.Primitives;

namespace Microsoft.Extensions.Options
{
    /// <summary>
    /// Implementation of <see cref="IOptionsMonitor{TOptions}"/>.
    /// </summary>
    /// <typeparam name="TOptions">Options type.</typeparam>
    public class OptionsMonitor<TOptions> : IOptionsMonitor<TOptions>, IDisposable where TOptions : class, new()
    {
        private readonly IOptionsMonitorCache<TOptions> _cache;
        private readonly IOptionsFactory<TOptions> _factory;
        private readonly IEnumerable<IOptionsChangeTokenSource<TOptions>> _sources;
        private readonly List<IDisposable> _registrations = new List<IDisposable>();
        internal event Action<TOptions, string> _onChange;

        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="factory">The factory to use to create options.</param>
        /// <param name="sources">The sources used to listen for changes to the options instance.</param>
        /// <param name="cache">The cache used to store options.</param>
        public OptionsMonitor(IOptionsFactory<TOptions> factory, IEnumerable<IOptionsChangeTokenSource<TOptions>> sources, IOptionsMonitorCache<TOptions> cache)
        {
            _factory = factory;
            _sources = sources;
            _cache = cache;

            foreach (var source in _sources)
            {
                var registration = ChangeToken.OnChange(
                      () => source.GetChangeToken(),
                      (name) => InvokeChanged(name),
                      source.Name);

                _registrations.Add(registration);
            }
        }

        private void InvokeChanged(string name)
        {
            name = name ?? Options.DefaultName;
            _cache.TryRemove(name);
            var options = Get(name);
            if (_onChange != null)
            {
                _onChange.Invoke(options, name);
            }
        }

        /// <summary>
        /// The present value of the options.
        /// </summary>
        public TOptions CurrentValue
        {
            get => Get(Options.DefaultName);
        }

        /// <summary>
        /// Returns a configured <typeparamref name="TOptions"/> instance with the given <paramref name="name"/>.
        /// </summary>
        public virtual TOptions Get(string name)
        {
            name = name ?? Options.DefaultName;
            return _cache.GetOrAdd(name, () => _factory.Create(name));
        }

        /// <summary>
        /// Registers a listener to be called whenever <typeparamref name="TOptions"/> changes.
        /// </summary>
        /// <param name="listener">The action to be invoked when <typeparamref name="TOptions"/> has changed.</param>
        /// <returns>An <see cref="IDisposable"/> which should be disposed to stop listening for changes.</returns>
        public IDisposable OnChange(Action<TOptions, string> listener)
        {
            var disposable = new ChangeTrackerDisposable(this, listener);
            _onChange += disposable.OnChange;
            return disposable;
        }

        /// <summary>
        /// Removes all change registration subscriptions.
        /// </summary>
        public void Dispose()
        {
            // Remove all subscriptions to the change tokens
            foreach (var registration in _registrations)
            {
                registration.Dispose();
            }

            _registrations.Clear();
        }

        internal class ChangeTrackerDisposable : IDisposable
        {
            private readonly Action<TOptions, string> _listener;
            private readonly OptionsMonitor<TOptions> _monitor;

            public ChangeTrackerDisposable(OptionsMonitor<TOptions> monitor, Action<TOptions, string> listener)
            {
                _listener = listener;
                _monitor = monitor;
            }

            public void OnChange(TOptions options, string name) => _listener.Invoke(options, name);

            public void Dispose() => _monitor._onChange -= OnChange;
        }
    }
}

3、最佳实践

既然有如此多的获取方式，那我们应该如何选择呢？

1、如果TOption不需要监控且整个程序就只有一个同类型的TOption，那么强烈建议使用IOptions<TOptions>。

2、如果TOption需要监控或者整个程序有多个同类型的TOption，那么只能选择IOptionsMonitor<TOptions>或者IOptionsSnapshot<TOptions>。

3、当IOptionsMonitor<TOptions>和IOptionsSnapshot<TOptions>都可以选择时，如果Action<TOptions>是一个比较耗时的操作，那么建议使用IOptionsMonitor<TOptions>，反之选择IOptionsSnapshot<TOptions>。

4、如果需要对配置源的更新做出反应时（不仅仅是配置对象TOptions本身的更新），那么只能使用IOptionsMonitor<TOptions>，并且注册回调。

本文部分内容参考博文：https://www.cnblogs.com/zhurongbo/p/10856073.html

选项模式微软官方文档：https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/configuration/options?view=aspnetcore-6.0

至此本文就全部介绍完了，如果觉得对您有所启发请记得点个赞哦！！！ 

 

aspnetcore源码：

链接：https://pan.baidu.com/s/1fszyRzDw9di1hVvPIF4VYg 
提取码：wz1j

Demo源码：

链接：https://pan.baidu.com/s/1F1vr2G4wXQv5obTd42xJjA 
提取码：4nax

此文由博主精心撰写转载请保留此原文链接：https://www.cnblogs.com/xyh9039/p/15943736.html

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