在.Net Core控制台应用程序中找不到依赖项-在启动时显示为丢失

Question

I'm having trouble getting any .Net Core 2.1 console application to build from scratch (or any kind of .Net Core/ASP.Net Core application for that matter). I posted a screenshot below that shows the errors (missing dependencies/references) and circled the Dependencies in the Solution Explorer as there's a yellow exclamation. I've also listed the "dotnet --info" command below as well as the "Output" window after trying to build. I cannot for the life of me figure out why my machine is not finding the Nuget packages/references on my machine. I really appreciate any help. I've tried many things like issuing a "dotnet restore" command. Deleting the NugetPackageFallBack folder, reparing Visual Studio and getting all updates. I'm using Visual Studio 15.7.4 on a Windows 10 machine x64.

Output of " dotnet --info "

C:\Projects\JDB_POC>dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   2.1.300
 Commit:    adab45bf0c

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.14393
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\2.1.300\

Host (useful for support):
  Version: 2.1.0
  Commit:  caa7b7e2ba

.NET Core SDKs installed:
  1.0.4 [C:\Program Files\dotnet\sdk]
  2.1.201 [C:\Program Files\dotnet\sdk]
  2.1.300 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 1.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]

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

Notice the yellow exclamation around the dependencies in the Solution Explorer

Output from the Output window:

1>C:\Users\RossJ\AppData\Local\Temp\.NETCoreApp,Version=v2.1.AssemblyAttributes.cs(4,20,4,26): error CS0400: The type or namespace name 'System' could not be found in the global namespace (are you missing an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(14,12,14,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(15,12,15,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(16,12,16,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(17,12,17,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(18,12,18,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(19,12,19,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(20,12,20,18): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>C:\Users\RossJ\AppData\Local\Temp\.NETCoreApp,Version=v2.1.AssemblyAttributes.cs(4,71,4,97): error CS0518: Predefined type 'System.String' is not defined or imported
1>C:\Users\RossJ\AppData\Local\Temp\.NETCoreApp,Version=v2.1.AssemblyAttributes.cs(4,99,4,119): error CS0246: The type or namespace name 'FrameworkDisplayName' could not be found (are you missing a using directive or an assembly reference?)
1>C:\Users\RossJ\AppData\Local\Temp\.NETCoreApp,Version=v2.1.AssemblyAttributes.cs(4,122,4,124): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(14,55,14,68): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(15,61,15,68): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(16,59,16,68): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(17,68,17,75): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(18,55,18,68): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(19,53,19,66): error CS0518: Predefined type 'System.String' is not defined or imported
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(20,55,20,64): error CS0518: Predefined type 'System.String' is not defined or imported
1>Program.cs(1,7,1,13): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>C:\Users\RossJ\AppData\Local\Temp\.NETCoreApp,Version=v2.1.AssemblyAttributes.cs(2,7,2,13): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>C:\Users\RossJ\AppData\Local\Temp\.NETCoreApp,Version=v2.1.AssemblyAttributes.cs(3,7,3,13): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(11,7,11,13): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>obj\Debug\netcoreapp2.1\ConsoleApp4.AssemblyInfo.cs(12,7,12,13): error CS0246: The type or namespace name 'System' could not be found (are you missing a using directive or an assembly reference?)
1>Program.cs(5,11,5,18): error CS0518: Predefined type 'System.Object' is not defined or imported
1>Program.cs(7,26,7,32): error CS0518: Predefined type 'System.String' is not defined or imported
1>Program.cs(7,16,7,20): error CS0518: Predefined type '

Answer 1

I had a similar issue to this. My working project all of a sudden had missing nuget packages. I tried all the suggestions above eg delete NugetFallBack Folder, clean solution, dotnet restore, etc. None worked. I tried creating a new project from scratch and it was missing packages on creation.

What fixed the issue for me was opening Visual Studio in Admin mode.