CODEWITHSUNDEEP
c#windowsvisual-studio-code.net-coreomnisharp
MStudley
MStudley

Reputation: 735

Error in Visual Studio Code Dotnet Core C#: "The type or namespace name 'System' could not be found", but build succeeds

When trying to work with Visual Studio Code on a C# DotNet Core MVC application, I am having a lot of trouble getting visual studio code to work. It is having trouble finding anything related to C#, marking even 'Using System;' as invalid, saying it can't find it.

However, when I run a Dotnet build, it succeeds with no warnings or errors and the project runs.

My project.json:

 {
  "version": "1.0.0-*",
  "buildOptions": {
    "debugType": "portable",
    "emitEntryPoint": true
  },
  "dependencies": {
    "Microsoft.NETCore.App": {
      "version": "1.1.0",
      "type": "platform"
    },
    "Microsoft.EntityFrameworkCore.Sqlite": "1.1.0",
    "Microsoft.EntityFrameworkCore.Design": {
      "version": "1.1.0",
      "type": "build"
    },
    "Microsoft.AspNetCore.Mvc": "1.1.0",
    "Microsoft.AspNetCore.Server.IISIntegration": "1.1.0",
    "Microsoft.AspNetCore.Server.Kestrel": "1.1.0",
    "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.1.0",
    "Microsoft.Extensions.Configuration.FileExtensions": "1.1.0",
    "Microsoft.Extensions.Configuration.Json": "1.1.0",
    "Microsoft.Extensions.Logging": "1.1.0",
    "Microsoft.Extensions.Logging.Console": "1.1.0",
    "Microsoft.Extensions.Logging.Debug": "1.1.0",
    "Microsoft.Extensions.Options.ConfigurationExtensions": "1.1.0",
    "Microsoft.AspNetCore.StaticFiles": "1.1.0"
  },

  "frameworks": {
    "netcoreapp1.1": {
      "dependencies": {
        "Microsoft.NETCore.App": {
          "type": "platform",
          "version": "1.1.0"
        }
      },
      "imports": "dnxcore50"
    }
  }
}

Any ideas? I'm really pulling my hair out with this one.

Upvotes: 64

Views: 60888

Answers (10)

Akshunya
Akshunya

Reputation: 433

If you are using the VS Code Extension 'C#' by Microsoft then try the following:-

For me doing the below two steps solved the issue:-

Go to File -> Preferences -> Settings

  1. Search omnisharp.useModernNet and set to false
  2. Search dotnet.server.useOmnisharp and set to true

Then Ctrl+Shift+P

-> Developer: Reload window

Upvotes: 10

urbanSoft
urbanSoft

Reputation: 760

Adding the configuration "omnisharp.useModernNet": true to the workspace settings.json solved the issue for me.

TL;DR

In my scenario I had a development environment with preinstalled Visual Studio 2017/2019 but the new .NET 6.0 was missing.

To overcome the missing of .NET 6.0 I set the variable omnisharp.useModernNet to false within the "User Settings (JSON)". A long time passed and I forgot about it...

Later I installed the .NET 6.0 SDK and created a new project. But with the useModernNet set to false vscode (OmniSharp) was unable to resolve the missing assemblys for the (now new) .NET 6.0 SDK.

Long stroy short: Setting the value to true in my workspace settings.json solved the issue for me in this special case.

Upvotes: 0

Vasanth R
Vasanth R

Reputation: 212

Same issue happened to me lot of times ..

in my case i opened the visual studio code as admin then run the teriminal command donet buid if required Restart OmniSharp (ctrl +shift + p)

Then It's working fine !!!

Upvotes: 0

ChrisRob
ChrisRob

Reputation: 1552

In my case vscode showed this error only for one file. The problem was solved by adding the missing file to the Assembly-CSharp.csproj I'm not sure when files are automatically added and when I do have to do it manually, but it solved this issue.

...
<ItemGroup>
    <Compile Include="Assets/Scripts/data/MissingFile.cs" />
...

Upvotes: 0

DRoveda
DRoveda

Reputation: 11

I'm using VS Code in a mac with OmniSharp and mono and the issue was gone after doing the following:

For MacOS and Linux users who have Mono installed, this means you will need to set omnisharp.useGlobalMono to never until a version of Mono ships with MSBuild 16.7.

Upvotes: 1

live-love
live-love

Reputation: 52386

If you get this error, you could be missing a package.

“The type or namespace name 'System' could not be found”

To add a package, you can run this command in the terminal:

dotnet add package

Example: Add Newtonsoft.Json NuGet package to a project:

dotnet add package Newtonsoft.Json

After that, go to the squiggly line, and add the missing reference by clicking on the lightbulb.

You can also install the Nuget Package Manager extension to find out what packages you need. See this answer to find out more:

Install a Nuget package in Visual Studio Code

Upvotes: 1

Daniel Mart&#237;nez Sarta
Daniel Mart&#237;nez Sarta

Reputation: 771

In VS Code on Fedora 30 with .NET Core 3.0 I had the same issue after create a worker project with dotnet new worker

First issue was that OmniSharp server didn't find the Sdks folder and the solution was include this line to the ~/.bashrc:

export MSBuildSDKsPath="/usr/share/dotnet/sdk/$(dotnet --version)/Sdks"

then restart VS Code, but C# extension show me some messages like:

The type or namespace name 'Collections' does not exist in the namespace 'System' (are you missing an assembly reference?)

the solution was, first, in the terminal run:

dotnet build

then restart the OmniSharp server using the command palette (Ctrl+Shift+P):

OmniSharp: Restart OmniSharp

then I restart VS Code and the C# extensions and all dependencies are working fine.

Upvotes: 20

esj51
esj51

Reputation: 1

Another possible cause of getting errors regarding "using System" is storing the .vscode directory in the git repository (my not adding it to .gitignore).

Opening the solution folder with VSCode can create cross version problems like the above and can be solved simply by deleting the .vscode directory.

Upvotes: -1

MStudley
MStudley

Reputation: 735

Ok, I've figured out what was causing the issue. I was referencing the wrong imports for the framework part of the project.json file.

This: 

"frameworks": {
    "netcoreapp1.1": {
      "dependencies": {
        "Microsoft.NETCore.App": {
          "type": "platform",
          "version": "1.1.0"
        }
      },
      "imports": "dnxcore50"
    }
  }

Should be this: 

"frameworks": {
    "netcoreapp1.1": {
      "imports": [
        "dotnet5.6",
        "portable-net45+win8"
      ]
    }
  }

I'm on a windows 8 machine, and for some reason "dnxcore50" isn't valid, but "dotnet5.6" and "portable-net45+win8" is. I'm going to keep looking at the why for this question, but I am posting this answer now in case someone else is dealing with this problem.

Upvotes: 1

Shaun Luttin
Shaun Luttin

Reputation: 141542

Sometimes C# for Visual Studio Code (powered by OmniSharp) becomes confused.

Try restarting OmniSharp. Here are two ways:

  1. Close and re-open Visual Studio Code, or
  2. Open the Command Pallet and type Restart Omnisharp.

OmniSharp tends to become confused if we restore dependencies from the command line instead of from within Visual Studio Code.

Upvotes: 145

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