升级至Xamarin.Forms 5后出现命名空间不存在问题求助

Hey there, let's work through these issues you're hitting after upgrading to Xamarin.Forms 5.0.0.1874. Most of these errors stem from big changes to Android dependencies in Xamarin.Forms 5.x—here's a step-by-step breakdown to fix them:

1. 核心问题：迁移到AndroidX #

Xamarin.Forms 5.0 completely dropped support for Xamarin.Android.Support libraries and switched to AndroidX instead. That's why you're seeing the "Support does not exist" error:

• Right-click your Android project → Properties → Go to the Application tab. Under the Android Manifest section, check the box for "Use AndroidX libraries" and click Apply. This auto-replaces all Support library references with their AndroidX equivalents.
• If auto-migration doesn't catch everything, manually uninstall all NuGet packages starting with Xamarin.Android.Support. and install the matching AndroidX packages (like Xamarin.AndroidX.AppCompat, Xamarin.AndroidX.Core, etc.).

2. Fix custom namespace errors (Net, Graphics, App) #

The missing MyProject.Android.* namespaces are likely due to project structure or reference shifts post-upgrade:

• Double-check that the files corresponding to these namespaces still exist in your Android project—they might've been accidentally moved or deleted.
• Verify your using statements are correct. For example, if your Android project uses the default Droid suffix (common in Xamarin projects), you might need to update references from MyProject.Android.App to MyProject.Droid.App.
• Go beyond just bin/obj cleanup: Delete the hidden .vs folder in your solution directory and any .csproj.user files, then restart Visual Studio and rebuild the solution from scratch.

3. Update your Android project's target framework #

Xamarin.Forms 5.0 requires your Android project to target at least Android 10.0 (API 29):

• Right-click the Android project → Properties → Application tab. In the "Compile using Android version (Target Framework)" dropdown, select Android 10.0 or higher.
• Also ensure your "Minimum Android version" is set to Android 8.0 (API 26) or above—this is the minimum requirement for Xamarin.Forms 5.0.

4. Check for namespace aliases or conflicts #

Sometimes old aliases or misaligned references cause these issues:

• Look for code like using Android = Xamarin.Android;—these aliases might need adjustment after the upgrade.
• For the missing App namespace, confirm your MainActivity is referencing the correct App class from your shared project, e.g., LoadApplication(new MyProject.App()); instead of MyProject.Android.App.

If none of these steps work, try creating a fresh Xamarin.Forms 5.0 project. Compare its NuGet references, project settings, and namespace structure to your existing project—this can help you spot misconfigurations you might've missed.

内容的提问来源于stack exchange，提问作者Innova