VS Installer「可用」选项卡无内容，无法安装Xamarin求助

Hey Alice, sorry to hear you're stuck trying to get Xamarin set up after updating Visual Studio 2019 Enterprise—let's work through some practical fixes that usually resolve this frustrating "Available" tab empty issue.

Here are the steps to try, in order of simplicity and success rate:

• Repair the VS Installer itself
  Sometimes the installer's own files get corrupted during updates. Close all Visual Studio-related programs first, then navigate to C:\Program Files (x86)\Microsoft Visual Studio\Installer\setup.exe, right-click it and select Run as administrator. Once open, click the More menu at the top right, then choose Repair. Let the process finish, restart the installer, and check the "Available" tab again.

• Clear the VS Installer cache
  Stale cache files can prevent the installer from fetching the latest component list. Close the installer, open File Explorer, and go to %ProgramData%\Microsoft\VisualStudio\Packages. Delete all contents in this folder (don't worry—the installer will re-download what it needs). Restart the installer and see if the "Available" tab populates.

• Check network/proxy settings
  The installer needs to connect to Microsoft's servers to load available components. Make sure your internet connection is stable. If you're using a proxy, try temporarily disabling it, or configure the proxy correctly in the installer: click the gear icon at the top right of VS Installer, go to Proxy Settings, and ensure the settings match your network configuration.

• Add Xamarin via the "Modify" tab instead
  If the "Available" tab stays empty, bypass it entirely. Switch to the Installed tab in VS Installer, find your Visual Studio 2019 Enterprise instance, click Modify. In the workloads list, locate Mobile development with .NET (this includes all Xamarin components), check the box next to it, then click Modify to start the installation.

• Reset the VS Installer
  If none of the above works, reset the installer to its default state. Open Command Prompt as an administrator, run this command:
  "%ProgramFiles(x86)%\Microsoft Visual Studio\Installer\resources\app\layout\Installer.exe" --repair --reset
  Wait for the command to complete, then restart the installer and try again.

These steps should cover most scenarios that cause the "Available" tab to be empty. If you still run into issues, you can check the VS Installer log files (located in %TEMP%\dd_setup_*.log) for more specific error details, but start with the fixes above—they're usually the quickest way to get back on track.

内容的提问来源于stack exchange，提问作者Alice