Prism使用Options选项

Options是微软提供的选项模块，该模块依赖于容器使用。除了微软的IServiceCollection，当然也可以使用其它的依赖注入容器。本文演示如何在prism中使用Options。

创建应用项目

创建一个Avalonia应用（或其它类型应用），然后使用NuGet包管理器添加Prism.DryIoc.Avalonia包。创建Views和ViewModels文件夹，将MainWindow移动到Views文件夹中（注意修改namespace），在ViewModels文件夹中创建MainWindowViewModel，以便Prism自动绑定ViewModel。

public partial class App : PrismApplication
{
    public override void Initialize()
    {
        AvaloniaXamlLoader.Load(this);
        base.Initialize();
    }

    protected override AvaloniaObject CreateShell()
    {
        return Container.Resolve<MainWindow>();
    }

    protected override void RegisterTypes(IContainerRegistry containerRegistry)
    {
        containerRegistry.Register<MainWindow>();
    }
}

添加Options功能

• 首先使用NuGet添加Microsoft.Extentions.Options和Microsoft.Extensions.Options.ConfigurationExtensions。使用json配置文件进行测试，因此再添加上Microsoft.Extensions.Configuration.Json及Microsoft.Extensions.Configuration.Binder。

• 添加Options静态类，提供DefaultName：

public static class Options
{
    public static readonly string DefaultName = string.Empty;
    internal const DynamicallyAccessedMemberTypes DynamicallyAccessedMembers =
        DynamicallyAccessedMemberTypes.PublicParameterlessConstructor;
}

• 由于UnnamedOptionsManager为内部类，无法直接使用，因此添加一个UnnamedOptionsManager类，实现IOptions<>接口，直接拷贝源码即可：

public class UnnamedOptionsManager<[DynamicallyAccessedMembers(Options.DynamicallyAccessedMembers)] TOptions> :
    IOptions<TOptions>
    where TOptions : class
{
    private readonly IOptionsFactory<TOptions> _factory;
    private volatile object _syncObj;
    private volatile TOptions _value;

    public UnnamedOptionsManager(IOptionsFactory<TOptions> factory) => _factory = factory;

    public TOptions Value
    {
        get
        {
            if (_value is TOptions value)
                return value;

            lock (_syncObj ?? Interlocked.CompareExchange(ref _syncObj, new object(), null) ?? _syncObj)
            {
                return _value ??= _factory.Create(Options.DefaultName);
            }
        }
    }
}

• 添加OptionsPrismExtensions扩展类，添加AddOptions扩展方法，将选项泛型接口、工厂、缓存注册到容器中。工厂注册为瞬时，其它注册为单例。客户端不需要添加IOptionsSnapshot，只添加IOptions<>和IOptionsMonitor<>即可，前者获取选项不会监听修改，后者可以监听选项修改：

public static class OptionsPrismExtensions
{
    public static IContainerExtension AddOptions(this IContainerExtension container)
    {
        ArgumentNullException.ThrowIfNull(container, nameof(container));

        container.RegisterSingleton(typeof(IOptions<>), typeof(UnnamedOptionsManager<>));
        container.RegisterSingleton(typeof(IOptionsMonitor<>), typeof(OptionsMonitor<>));
        container.Register(typeof(IOptionsFactory<>), typeof(OptionsFactory<>));
        container.RegisterSingleton(typeof(IOptionsMonitorCache<>), typeof(OptionsCache<>));
        return container;
    }
}

• 添加OptionsConfigurationPrismExtensions扩展类，提供Configuration相关的扩展方法，可以直接将选项和配置Section进行绑定：

public static class OptionsConfigurationPrismExtensions
{
    public static IContainerExtension Configure<[DynamicallyAccessedMembers(
        DynamicallyAccessedMemberTypes.All)] TOptions>(this IContainerExtension container, 
        IConfiguration config) where TOptions : class
        => container.Configure<TOptions>(Options.DefaultName, config, _ => { });

    public static IContainerExtension Configure<[DynamicallyAccessedMembers(
        DynamicallyAccessedMemberTypes.All)] TOptions>(this IContainerExtension container, 
        string name, IConfiguration config, Action<BinderOptions> configureBinder)
        where TOptions : class
    {
        ArgumentNullException.ThrowIfNull(container, nameof(container));
        ArgumentNullException.ThrowIfNull(config, nameof(config));
    
        container.AddOptions();
        container.RegisterInstance<IOptionsChangeTokenSource<TOptions>>(
            new ConfigurationChangeTokenSource<TOptions>(name, config));
        container.RegisterInstance<IConfigureOptions<TOptions>>(
            new NamedConfigureFromConfigurationOptions<TOptions>(name, config, configureBinder));
    
        return container;
    }
}

使用

• 添加一个settings.json配置文件，设置属性复制到输出目录：如果较新则复制：

{
  "Test": {
    "Name": "louzi",
    "Age": 18,
    "Sex": "Male"
  }
}

• 添加Test对应的Option实体：

public class TestOption
{
    public string Name { get; set; }

    public int Age { get; set; }

    public Gender Sex { get; set; }
}

public enum Gender
{
    Male,
    Female
}

• 创建IConfiguration并绑定到选项：

// App
protected override IContainerExtension CreateContainerExtension()
{
    var container =  base.CreateContainerExtension();

    IConfiguration config = new ConfigurationBuilder().SetBasePath(Directory.GetCurrentDirectory())
        .AddJsonFile("settings.json", optional: true, reloadOnChange: true).Build();
    container.AddOptions().Configure<TestOption>(config.GetSection("Test"));

    return container;
}

• ViewModel中通过依赖注入获取选项：

public class MainWindowViewModel : BindableBase
{
    private string _name;
    private int _age;
    private Gender _sex;

    public MainWindowViewModel(IOptions<TestOption> options)
    {
        var testOption = options.Value;
        _name = testOption.Name;
        _age = testOption.Age;
        _sex = testOption.Sex;
    }

    public string Name { get => _name; set => SetProperty(ref _name, value); }

    public int Age { get => _age; set => SetProperty(ref _age, value); }

    public Gender Sex { get => _sex; set => SetProperty(ref _sex, value); }
}

• View中显示

<Grid RowDefinitions="1*,1*,1*" ColumnDefinitions="1*,1*">
	<TextBlock Text="Name: " TextAlignment="Right"/>
	<TextBlock Text="{Binding Name}" Grid.Column="1"/>
	<TextBlock Text="Age: " Grid.Row="1" TextAlignment="Right"/>
	<TextBlock Text="{Binding Age}" Grid.Row="1" Grid.Column="1"/>
	<TextBlock Text="Sex: " Grid.Row="2" TextAlignment="Right"/>
	<TextBlock Text="{Binding Sex}" Grid.Row="2" Grid.Column="1"/>
</Grid>

项目结构及运行效果如下图：