The type or namespace name 'App' could not be found (are you missing a using directive or an assembly reference?) [Blazor] [14, 30]

[mammadkoma]

I have installed these dotnet cores :
2.1.505 [C:\Program Files\dotnet\sdk]
2.2.101 [C:\Program Files\dotnet\sdk]
2.2.105 [C:\Program Files\dotnet\sdk]
3.0.100-preview3-010431 [C:\Program Files\dotnet\sdk]

I created a blazor project named Blazor. project builds and run by command or powershell correctly. but when open project folder by vs code it shows an error in PROBLEMS window :
The type or namespace name 'App' could not be found (are you missing a using directive or an assembly reference?) [Blazor] [14, 30]

vs code version : 1.32.3
c# version : 1.18.0

OUTPUT window :

Starting OmniSharp server at 3/29/2019, 10:37:20 PM
Target: d:\MyProjects\Core\Blazor

OmniSharp server started.
Path: C:\Users\mammadkoma.vscode\extensions\ms-vscode.csharp-1.18.0.omnisharp\1.32.11\OmniSharp.exe
PID: 5272

Starting OmniSharp on Windows 6.2.9200.0 (x64)
info: OmniSharp.Services.DotNetCliService
DotNetPath set to dotnet
info: OmniSharp.MSBuild.Discovery.MSBuildLocator
Located 2 MSBuild instance(s)
1: Visual Studio Enterprise 2017 15.9.28307.557 - "C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin"
2: StandAlone 15.0 - "C:\Users\mammadkoma.vscode\extensions\ms-vscode.csharp-1.18.0.omnisharp\1.32.11\msbuild\15.0\Bin"
info: OmniSharp.MSBuild.Discovery.MSBuildLocator
Registered MSBuild instance: Visual Studio Enterprise 2017 15.9.28307.557 - "C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\MSBuild\15.0\Bin"
info: OmniSharp.Cake.CakeProjectSystem
Detecting Cake files in 'd:\MyProjects\Core\Blazor'.
info: OmniSharp.Cake.CakeProjectSystem
Could not find any Cake files
info: OmniSharp.WorkspaceInitializer
Project system 'OmniSharp.DotNet.DotNetProjectSystem' is disabled in the configuration.
info: OmniSharp.MSBuild.ProjectSystem
No solution files found in 'd:\MyProjects\Core\Blazor'
info: OmniSharp.MSBuild.ProjectManager
Queue project update for 'd:\MyProjects\Core\Blazor\Blazor.csproj'
info: OmniSharp.Script.ScriptProjectSystem
Detecting CSX files in 'd:\MyProjects\Core\Blazor'.
info: OmniSharp.Script.ScriptProjectSystem
Could not find any CSX files
info: OmniSharp.WorkspaceInitializer
Invoking Workspace Options Provider: OmniSharp.Roslyn.CSharp.Services.CSharpWorkspaceOptionsProvider
info: OmniSharp.MSBuild.ProjectManager
Loading project: d:\MyProjects\Core\Blazor\Blazor.csproj
info: OmniSharp.WorkspaceInitializer
Configuration finished.
info: OmniSharp.Stdio.Host
Omnisharp server running using Stdio at location 'd:\MyProjects\Core\Blazor' on host 4292.
info: OmniSharp.MSBuild.ProjectManager
Successfully loaded project file 'd:\MyProjects\Core\Blazor\Blazor.csproj'.
info: OmniSharp.MSBuild.ProjectManager
Adding project 'd:\MyProjects\Core\Blazor\Blazor.csproj'
info: OmniSharp.MSBuild.ProjectManager
Update project: Blazor

[akshita31]

@NTaylorMullen Is this something related to razor extension ?

[NTaylorMullen]

Yup, absolutely is, thanks @akshita31!

@mammadkoma that's a current limitation of the VSCode Razor experience. We're adding support for Blazor in the next release which should be this month. Stay tuned!

[mammadkoma]

Flutter framework from google works and run with microsoft vscode correctly.
But blazor framework from microsoft don't work and run (F5) with microsoft vscode!

[mammadkoma]

This issue is caused by an extension, please file it with the repository (or contact) the extension has linked in its overview in VS Code or the marketplace for VS Code. See also our issue reporting guidelines.

Happy Coding!

microsoft/vscode#72701 (comment)

[smj0x]

same issue anyone know how to resolve it?

[noamichael]

@smjltd I was having the same issue. It turns out that my dotnet cli was outdated. I grabbed the latest preview build from here and the app worked after installation when I ran dotnet run in the project's root directory.

[moboer]

@noamichael thank you

[elishnevsky]

2 years later and I still have this issue with .NET 5.0 and the latest version of VS Code and C# extension. Is there a solution?

[Cyber1000]

having the same problem with dotnet 6.0, latest vscode (1.64.2) and omnisharp (1.2.4.0), building with dotnet build works without problem, but I'm getting still this kind of "problem". It is running within a docker-container (if that matters).
Why is this issue closed?