找不到指定的框架“Microsoft.AspNetCore.App”，版本“2.1.0”

我嘗試將我的網路應用程序從 .net core 2.0 升級到 .net core 2.1 我做了：

1. 安裝 Visual Studio Professional 2017 Preview Version 15.8.0 Preview 1.1

2. 從此處安裝 .net core 2.1.3 RC1 SDK：https ://www.microsoft.com/net/download/dotnet-core/sdk-2.1 .300-rc1

3. 將我所有的 aspnetcore nuget 包更新到最新版本。

完成這兩件事後，當我開始我的項目時，我會看到這個螢幕：

HTTP 錯誤 502.5 - 程序失敗 此問題的常見原因：

The application process failed to start
The application process started but then stopped
The application process started but failed to listen on the configured port 

故障排除步驟：

Check the system event log for error messages
Enable logging the application process' stdout messages
Attach a debugger to the application process and inspect 

有關詳細資訊，請訪問： https ://go.microsoft.com/fwlink/?LinkID=808681

在 ASP.NET Core Web 伺服器的輸出視窗中，我得到了這個：

The specified framework 'Microsoft.AspNetCore.App', version '2.1.0' was not found.
 - Check application dependencies and target a framework version installed at:
     C:\Program Files\dotnet\
 - Installing .NET Core prerequisites might help resolve this problem:
     http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
 - The .NET Core framework and SDK can be installed from:
     https://aka.ms/dotnet-download
 - The following versions are installed:
     2.1.0-preview2-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
     2.1.0-rc1-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
It was not possible to find any compatible framework version
The specified framework 'Microsoft.AspNetCore.App', version '2.1.0' was not found.
 - Check application dependencies and target a framework version installed at:
     C:\Program Files\dotnet\
 - Installing .NET Core prerequisites might help resolve this problem:
     http://go.microsoft.com/fwlink/?LinkID=798306&clcid=0x409
 - The .NET Core framework and SDK can be installed from:
     https://aka.ms/dotnet-download
 - The following versions are installed:
     2.1.0-preview2-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
     2.1.0-rc1-final at [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]

.NET Core 2.1 SDK 將於本週發布。如果您不能等到那時，請將其添加到您的 *.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">
 <PropertyGroup>
   <TargetFramework>netcoreapp2.1</TargetFramework>
   <RestoreAdditionalProjectSources>
       https://dotnetfeed.blob.core.windows.net/orchestrated-release-2-1/20180515-07/final/index.json
   </RestoreAdditionalProjectSources>
 </PropertyGroup>
 
 ....
</Project>

並從以下網址下載最終 SDK：https ://dotnetcli.blob.core.windows.net/dotnet/Sdk/2.1.300/dotnet-sdk-2.1.300-win-x64.exe

更多詳情請訪問：https ://github.com/aspnet/Home/wiki/2.1.0-Early-Access-Downloads

引用自：https://stackoverflow.com/questions/50594020