how to resolve "Unable to find package" nuget error

Solution 1:

The package source was offline !!

I installed VS2017 professional on my system and opened an existing project and found that multiple packages were missing. I tried everything I could, without looking at Package Source !!

I am writing this answer as I tried the below solutions but none of them worked :

1. Clearing the cache
2. Restoring or re-installing the packages
3. Changing the targetFramework
4. Updating the Nuget Package manager

Solution:

Step 01. Go to Package Manager Settings (Tools > Nuget Package Manager > Package Manager Settings)

Step 02. Check the Package Source(s). As you can see, the package source is here already downloaded SDK/nugets/packages. I don't know the reason but the online package source from nuget.org was missing from my system installation of Visual Studio.

Step 03. Install the nuget.org as package source and then 'Clear All Nuget Cache(s)' and then restore the packages. The error will go away.

Name: nuget.org ( or as you wish) Source: https://api.nuget.org/v3/index.json

Solution 2:

I just did this and it went fine. In your Visual Studio, go to:

1. Tools
2. Nuget Package Manager
3. General
4. Click button "Clear All Nuget Cache(s)
5. Package Resources and click "Update"
6. Woolah! Error gone...

Solution 3:

GitHub Actions

I would like to add that in Github Actions, the nuget.org repository is not queried by default. Instead GitHub defaults to a cached package repository and it might happen that your referenced package is not in that cache but is on nuget.org (I had that for System.CommandLine).

You can fix this by adding a nuget.config file to your root directory containing the following

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <packageSources>
    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
  </packageSources>
</configuration>

Example github_action.yml file

name: .NET

on:
  push:
    branches: [ master ]
  pull_request:
    branches: [ master ]

jobs:
  build:

    runs-on: windows-latest

    steps:
    - uses: actions/checkout@v2
    - name: Setup .NET
      uses: actions/setup-dotnet@v1
      with:
        dotnet-version: 5.0
    - name: Clean
      run: dotnet clean && dotnet nuget locals all --clear
    - name: Restore dependencies
      run: dotnet restore
    - name: Build
      run: dotnet build --no-restore
    - name: Test
      run: dotnet test --no-build --verbosity normal

Solution 4:

for me: %appdata%\NuGet\NuGet.Config contained only <activePackageSource> <add key="nuget.org" value="https://www.nuget.org/api/v2/" /> </activePackageSource>

after doing

nuget sources add -Name "NuGet official package source" -Source "https://api.nuget.org/v3/index.json"

this was added

  <packageSources>
    <add key="https://www.nuget.org/api/v2/" value="https://www.nuget.org/api/v2/" />
    <add key="NuGet official package source" value="https://api.nuget.org/v3/index.json" />
  </packageSources>

afterwards packeges were found.