找不到系统 Visual Studio 2017 ASP.NET Core 项目

I had the same issue in my Visual studio 2017 .Net Core application. I closed the Visual studio and re-open fixed everything.

Came across the same issue today. I had an old nuget source that no longer existed. So I went into Tools > Nuget Packet Manager and un-checked the wrong one. Hit "Ok", and then rebuilt the project, and it works great now. It seems like you stumbled onto it, but also wanted to verify that it fixed my issue, and it does.

https://i.stack.imgur.com/JVmWm.png

I had the same problem, first when converting a VS2015 net core mvc web project to 2017 and then when trying to create a new core web application in 2017.

Went to Tools|NuGet Package Manager|Package Manager Settings - checked 'Allow NuGet to download missing packages' and 'Automatically check for missing packages during build in VS' and then clicked 'Clear All NuGet Cache(s)'.

Then re-built the solution - it found and loaded all the required packages and ran OK.

May not work for all cases but simple and worth a try.

Multiple closing and reopening of VS2017 fixed it for me.

I had the same issue, the solution for me was to clear the NuGet cache. Tools > NuGet Package Manager > Package Manager Settings > Clear All NuGet Cache(s)

Check the version .NET Command Line Tools in CMD, just type dotnet --info. If version is 1.0.0, then try to install latest version .NET Core SDK from here.

https://i.stack.imgur.com/01XGo.png

I have had the same issue with Visual Studio 2019 and .NET Core SDK 2.2.

These steps solved the problem:

Close the Visual Studio Open the Visual Studio as Administrator Open the Solution Right click on Solution -> Restore NuGet Packages

I've tried all answers above. For me works only removal and adding the reference again described in the following steps:

Open 'References' under the project. Right click on 'System' reference. Click on 'Remove'. Right click on 'References'. Click 'Add Reference...'. From right menu choose an 'Assemblies', In a search field type 'System'. Choose 'System' from the list. Click 'Add' button. IMPORTANT: Restart the Visual Studio.

'System' reference you can replace with any you need.

Find the broken project and right click, Unload, right click, Re-load. Fastest fix for me.

If you get the problem while using the CLI, try doing nuget restore instead of dotnet restore as that sometimes pulls down packages that the dotnet CLI seems to miss.

Try adding the following line above the other references in the csproj file

<Reference Include="netstandard" />

https://i.stack.imgur.com/COnPv.png

For me the problem was caused by my project having a custom IntermediateOutputPath. For some reason, if project_name.csproj.nuget.g.targets is not in obj subfolder of project folder, the error occurs.

Using default IntermediateOutputPath or keeping a shadow copy of project_name.csproj.nuget.g.targets in fake obj folder solves the problem for me.

This issue seems to be triggered by a myriad of reasons. Mine was caused by cloning directly from VSTS using Git Bash, my project directory had spaces in it. Git Bash changed those spaces in the path to %20. It was throwing off all the references in my project. So for anyone who tried everything else and are at their wits end, make sure %20 is not in the path.

So, I have cloned the repository from github and started getting this error.

It was my project uploaded from another machine. I later realized that I have used the materialdesign packages in my project.

I have uninstalled and reinstalled these packages and it fixed my issue.

Had the same problem. Uninstalled Application Insights from my projects using the nuget package manager. I'm not looking at that yet, I just wanted core and unit tests. Problem solved.

I also had the same problem. The is no SDK folder under the Dependencies one. Therefore, no Microsoft.NetCore.App libraries !

To solve this problem, in Nuget manager window, install any nuget which depends on .NetCoreApp (you can install for example Microsoft.AspNetCore or BundlerMinifier.Core from the Microsoft Visual Studio Offline Packages source).

The SDK will be restored by the same time.

Once it is back, you can uninstall the previously added nuget. The SDK will remain in place.

Not quite sure in which order vs 2017 trying to resolve packages. But my situation was following. In my VS2015 I had configured local and 3rd party source for nuget packages, newly installed version of 2017 loaded them too.

https://api.nuget.org/v3/index.json was first in list.

But vs2017 throwed an error that it can't restore .net core libraries from my another local repo.

After I unchecked all of them except https://api.nuget.org/v3/index.json, it had started to working normally.

I had this problem too, but not right now, this steps solved my problem: Choose Project -> Properties from the menu bar. In the Project properties window, under Configuration Properties -> General, make sure that Common Language Runtime Support is set to Common Language Runtime Support (/clr)

Simply opening the NuGet package manager and then the Visual Studio settings related to it - without changing anything - merely looking around, and when I closed out, the problem was gone.

This seems to be an intermittent issue that can come and go for no obvious reason.

None of the answers here worked for me so I'm posting what did work. My errors were mostly the same as the original poster but I also had:

Error loading meta data for 'Microsoft.Extensions.FileProviders.Embedded.2.0.1' hexadecimal value 0x1C invalid character

Every time I attempted to download a different nuget package or restore old packages I would see this error. I also saw the other errors such as:

type or namespace system could not be found

What worked for me:

opened the filepath that the error said the bad metadata was in, which for me was C:\Program Files\dotnet\sdk\NuGetFallbackFolder\microsoft.extensions.fileproviders.embedded\2.0.1 Then, I put the contents of that folder into another folder I named "hiding". Then, I went back to the nuget package manager and tried to install a package, hoping to have the SDK restored. IOt worked successfully, and all my other errors were gone as well, and the fresh new project runs as it should!

The problem for me occurred when running my Visual Studio as Admin with a separate user-- I had created a Git Repo with the source files in the user documents of my normal account. When I created a new solution in that folder the above errors occurred. Try creating your project in a different place and see if the error still occurs.

I was facing the same issue when I created a new project (.net Core 2.2) in VS2019.In my case there was an Azure package which was creating the problem.I uninstalled it and the project started working fine. Run mentioned below command to uninstall the package.

Uninstall-Package Microsoft.VisualStudio.Azure.Containers.Tools.Targets -Version 1.7.10

I had the same problem. I cloned a github project and this error came. So I deleted the cloned project and then I cloned the project again and it worked fine.