.Net FW上线报错：The OwinStartup attribute discovered in assembly 'AppName'.

阅文时长	| 2.32分钟	字数统计	| 3726.4字符
主要内容	| 1、引言&背景 2、解决方案 3、声明与参考资料
『.Net FW上线报错：The OwinStartup attribute discovered in assembly 'AppName'.』
编写人	| SCscHero	编写时间	| 2022/2/18 PM8:20
文章类型	| 系列	完成度	| 已完成
座右铭	每一个伟大的事业，都有一个微不足道的开始。

一、引言&背景   完成度：100%

a) 应对问题

近日上线遇到个问题，主要异常为：The OwinStartup attribute discovered in assembly 'AppName' referencing startup type 'AppName.Startup' conflicts with the attribute in assembly 'AppName' referencing startup type 'AppName.Startup' because they have the same FriendlyName ''.Remove or rename one of the attributes, or reference the desired type directly.看异常描述和一个OwinStartup的依赖项有关。

详细异常信息如下：

Server Error in '/' Application.
The following errors occurred while attempting to load the app.
- The OwinStartup attribute discovered in assembly 'SCOnlineWeb' referencing startup type 'SCOnlineWeb.Startup' conflicts with the attribute in assembly 'SCOnlineHosting' referencing startup type 'SCOnlineHosting.Startup' because they have the same FriendlyName ''. Remove or rename one of the attributes, or reference the desired type directly.
To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config.
To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 

Exception Details: System.EntryPointNotFoundException: The following errors occurred while attempting to load the app.
- The OwinStartup attribute discovered in assembly 'SCOnlineWeb' referencing startup type 'SCOnlineWeb.Startup' conflicts with the attribute in assembly 'SCOnlineHosting' referencing startup type 'SCOnlineHosting.Startup' because they have the same FriendlyName ''. Remove or rename one of the attributes, or reference the desired type directly.
To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config.
To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.

Source Error: 

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace: 

[EntryPointNotFoundException: The following errors occurred while attempting to load the app.
 - The OwinStartup attribute discovered in assembly 'SCOnlineWeb' referencing startup type 'SCOnlineWeb.Startup' conflicts with the attribute in assembly 'SCOnlineHosting' referencing startup type 'SCOnlineHosting.Startup' because they have the same FriendlyName ''. Remove or rename one of the attributes, or reference the desired type directly.
To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config.
To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.]
   Microsoft.Owin.Host.SystemWeb.OwinBuilder.GetAppStartup() +470
   Microsoft.Owin.Host.SystemWeb.OwinHttpModule.InitializeBlueprint() +37
   System.Threading.LazyInitializer.EnsureInitializedCore(T& target, Boolean& initialized, Object& syncLock, Func`1 valueFactory) +135
   Microsoft.Owin.Host.SystemWeb.OwinHttpModule.Init(HttpApplication context) +160
   System.Web.HttpApplication.RegisterEventSubscriptionsWithIIS(IntPtr appContext, HttpContext context, MethodInfo[] handlers) +580
   System.Web.HttpApplication.InitSpecial(HttpApplicationState state, MethodInfo[] handlers, IntPtr appContext, HttpContext context) +165
   System.Web.HttpApplicationFactory.GetSpecialApplicationInstance(IntPtr appContext, HttpContext context) +267
   System.Web.Hosting.PipelineRuntime.InitializeApplication(IntPtr appContext) +341

[HttpException (0x80004005): The following errors occurred while attempting to load the app.
 - The OwinStartup attribute discovered in assembly 'SCOnlineWeb' referencing startup type 'SCOnlineWeb.Startup' conflicts with the attribute in assembly 'SCOnlineHosting' referencing startup type 'SCOnlineHosting.Startup' because they have the same FriendlyName ''. Remove or rename one of the attributes, or reference the desired type directly.
To disable OWIN startup discovery, add the appSetting owin:AutomaticAppStartup with a value of "false" in your web.config.
To specify the OWIN startup Assembly, Class, or Method, add the appSetting owin:AppStartup with the fully qualified startup class or configuration method name in your web.config.]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) +523
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +107
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +688

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.7.3770.0

b) 应用场景

• .Net FW项目异常。

二、解决方案   完成度：100%

a) 分析检查

检查是否有引用Microsoft.Owin的依赖，如有则需要配置了。

using Microsoft.Owin;
using Microsoft.Owin.Builder;
using Owin;

[assembly: OwinStartupAttribute(typeof(SCOnlineHosting.Startup))]
namespace SCOnlineHosting
{
    public partial class Startup {
        public void Configuration(AppBuilder app) {
            ConfigureAuth(app);
        }
    }
}

b) 配置web.config

可在配置文件中添加appsetting：

<add key="owin:AutomaticAppStartup" value="false"/>

三、声明与参考资料   完成度：100%

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