无法在Xamarin中安装/更新Facebook.Android包及相关支持库

Hey there, let’s break this down into two parts since you’ve got two distinct issues to fix—these are super common Xamarin headaches, but we can work through them step by step.

Part 1: Resolving Package Restore Failures for Facebook.Android & Support Libraries #

The "Package restore failed. Rolling back package changes" error usually stems from dependency conflicts, corrupted caches, or misconfigured NuGet settings. Try these steps:

• Double-check your NuGet sources
  Sometimes outdated or third-party sources can block valid package downloads. Head to Tools > Options > NuGet Package Manager > Package Sources and make sure the official nuget.org source is enabled and at the top of the list. Temporarily disable any other sources to rule out conflicts.

• Clear your NuGet cache thoroughly
  Corrupted cached packages are a frequent culprit. Even if you deleted files manually, running the official command ensures you wipe all cached data:
  Open a command prompt and run:

  dotnet nuget locals all --clear
  

  If you’re using the older NuGet CLI, use:

  nuget locals all -clear
  

• Verify your project’s target Android framework
  The Xamarin Support libraries and Facebook.Android have strict minimum Android version requirements. Right-click your Android project > Properties > Application > Target Framework and ensure it’s set to a version that matches the packages’ needs (typically Android 10.0 or higher for newer support library versions).

• Uninstall and reinstall packages in order
  Dependency chaos can happen if packages are installed out of order. First, uninstall all problematic support libraries (Xamarin.Android.Support.Design, v7.AppCompat, etc.) and Facebook.Android. Then reinstall them in this sequence:

  1. Xamarin.Android.Support.v4
  2. Xamarin.Android.Support.v7.AppCompat
  3. Xamarin.Android.Support.v7.CardView
  4. Xamarin.Android.Support.v7.MediaRouter
  5. Xamarin.Android.Support.Design
  6. Facebook.Android

• Clean up your project file
  If conflicts linger, open your Android project’s .csproj file in a text editor. Look for duplicate or mismatched version references (e.g., two different versions of the same support library). Remove any redundant entries, save the file, and try restoring packages again.

Part 2: Fixing "Access to the path xamarin.forms.build.tasks.dll is denied" #

This error happens when a process locks the DLL file, or you lack permissions to modify it. Try these fixes:

• Fully close Visual Studio and related processes
  Visual Studio or background MSBuild processes might be holding a lock on the file. Close all VS windows, then open Task Manager and end any lingering msbuild.exe or Xamarin processes.

• Manually delete cache and project files
  Navigate to these folders and delete the relevant files:

  • NuGet Xamarin.Forms cache: %USERPROFILE%\.nuget\packages\xamarin.forms (delete the version folder causing issues)
  • Project bin/obj folders: Right-click your project > Clean, then manually delete any remaining files in bin and obj if the clean fails
  • Xamarin system cache: %LOCALAPPDATA%\Xamarin (delete old cache folders here)

• Run Visual Studio as Administrator
  Permission issues are often fixed by elevating VS. Right-click the Visual Studio icon and select Run as administrator, then try cleaning your solution and restoring packages again.

• Check your antivirus software
  Antivirus tools sometimes flag Xamarin DLLs as suspicious and lock them. Temporarily disable your antivirus or add these folders to its exclusion list:

  • %USERPROFILE%\.nuget\packages
  • Your project’s root directory

Hope these steps get you back on track—Xamarin can be picky with dependencies, but a little cache clearing and configuration tweaking usually does the trick!

内容的提问来源于stack exchange，提问作者Laszlo