Nuget Package ...在项目中不存在...包...已经存在于文件夹中

Question

I've been fighting with this error for several hours and can't come up with a solution that works.

I have an ASP.Net API within a multi-project solution which has its references/dependencies improperly configured and I've been trying to fix it for two days.

The issue is ( I believe ) that the API is missing System.Web.Http / System.Web.Http.WebHost which apparently is included with Microsoft.AspNet.WebApi.Core (per multiple other Stack Overflow questions). When trying to install it via Nuget I get the following error when attempting to resolve the dependency. Further I've gotten this error every time (see my troubleshooting later in this question):

I've done the following steps in no particular order (multiple times each in various combinations):

• Run 'Update-package Microsoft.AspNet.WebApi.Core -reinstall'
• Delete the solution-wide "Packages" folder and delete the project's packages.config and attempt to restore packages
• Delete the entire project from the physical drive and TFS, and recreate it from scratch (it creates with the references incorrect)
• Install the package via both the command line and Nuget GUI
• Check the solution out to different locations on my hard drive in an attempt to start as fresh as possible
• Reboot my computer/Restart Visual Studio

At this point I'm fine with a non-clean fix, as long as it fixes it. The API was working at one point, but then I checked it into TFS, created a branch, and am now working on the branch. Possibly some dependencies weren't included (?) but even if this was the case it seems like the steps I've taken should resolve the issue.

Answer 1

Close the solution then go to the packages folder on your hard drive and delete all its contents. Open your application again in Visual Studio and it will automatically try to restore the packages. Clean the Solution and Build it.

Answer 2

Clearing the cache solved the problem for me. There's an option to clear the cache on Tools > Options > NuGet Package Manager > General menu, called Clear All NuGet Cache(s) .

Answer 3

First, uninstall via package manager console the specific NuGet package

Then, please unload the project where this nugget package was referenced for by right click -> Unload Project.

After unloading right click in the project and select "Edit {Project Name}.csproj"

Find the NuGet package entry within the XML where you previously uninstalled and delete it.

Install again the package from package manager console...

Answer 4

None of the other answers worked for me. It kept going in an endless loop of install, revert, restart VS, never making any progress.

What I ended up having to do was:

1. Close VS.
2. Delete the offending packages from the packages folder.
3. Edit the packages.config file manually, adding the package names and versions I needed to install.
4. When I opened the solution again, I right-clicked the project and said "manage NuGet packages" and clicked the "Restore" button that appeared on the banner. This installed the packages that refused to install.

For crying out loud! Microsoft needs to take a lesson from yarn on how to do package management properly.