有个报错：The current .NET SDK does not support targeting .NET Standard 2.0.

于是目光开始关注 .NET Core :

• Download : https://dotnet.microsoft.com/download
• Docs: https://docs.microsoft.com/en-us/dotnet/core/
  

延伸阅读：

• 微软Visual Studio 2019正式版发布
  https://www.ithome.com/0/417/422.htm