对于 vs2017，需要设置一个用户变量 MSBuildSDKsPath，值为 C:\Program Files\dotnet\sdk\2.2.110\Sdks，我这样设置后再打开或新建都不会弹这个错误了。

如果使用 vs2019，那么用 dotnet core 的 2.2.2xx 版本就可以了。
最新版的 .net core 2.2.2xx 只能用于 vs2019，不兼容 vs2017。
查找 vs 2017 或 vs 2019 要选择哪个 net core 版本。
https://dotnet.microsoft.com/download/visual-studio-sdks

用 dotnet --info 查看当前的 .net 信息。

C:\Users\Administrator>dotnet --info
.NET Core SDK（反映任何 global.json）:
 Version:   2.2.207
 Commit:    f7b16a2cd5

运行时环境:
 OS Name:     Windows
 OS Version:  10.0.18362
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.2.207\

Host (useful for support):
  Version: 2.2.8
  Commit:  b9aa1abc51

.NET Core SDKs installed:
  1.1.6 [C:\Program Files\dotnet\sdk]
  2.1.2 [C:\Program Files\dotnet\sdk]
  2.2.100 [C:\Program Files\dotnet\sdk]
  2.2.110 [C:\Program Files\dotnet\sdk]
  2.2.207 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 1.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download