Predefined type 'System.Object/String' is not defined or imported

Question

I have created the default ASP .NET Core MVC app in Visual Studio 2017 and there are 100+ errors and 44 warnings. The errors are:

1. Predefined type 'System.Object' is not defined or imported
2. Predefined type 'System.String' is not defined or imported
3. Predefined type 'System.Int32' is not defined or imported

I have tried these: - restart and reinstall VS - delete the bin and obj folders - rebuild the project - dotnet restore reopen the project in VS

project: https://github.com/martin-petrov03/Demo/tree/master/Ex

Answer 1

I recently experience the same. I eventually fixed the issue by removing the offending projects from the solution and then re-adding them (you can actually just 'unload' them).

Answer 2

I encountered this problem today too. It turned out that adding this text:

  <ItemGroup>
    <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform">
      <Version>6.2.10</Version>
    </PackageReference>
  </ItemGroup>

into my UWP.csproj caused the problem to go away

Answer 3

Removing the bindings to other projects and re-adding them works for me, thank you for your suggestion @Trevor !!