Register Attribute breaks build

[ray-geberit]

RegisterException.zip

Android framework version

net10.0-android (Preview)

Affected platform version

VS 2026 18.1.1, .Net 10.0.1 (also 10.0.0)

Description

As soon as i set the "Register("ViewName") attribute to a View in .Net for Android, it breaks the build with an "InvalidOperationException" when i try to rebuild the project.

Steps to Reproduce

1. File -> New Android Project
2. Create a CustomView that inherits from Android.Views.View --> building the project is fine
3. Add the Attribute "Register("CustomView") to the class. --> building the project fails

With .net 9 this worked fine.

Did you find any workaround?

No, i didn't find a workaround

Relevant log output

System.InvalidOperationException: Missing required attribute 'package'
   at Java.Interop.Tools.JavaCallableWrappers.Extensions.XmlExtensions.GetRequiredAttribute(XElement xml, String name)
   at Java.Interop.Tools.JavaCallableWrappers.Adapters.XmlImporter.ImportType(XElement xml)
   at Java.Interop.Tools.JavaCallableWrappers.Adapters.XmlImporter.Import(XElement xml)
   at Xamarin.Android.Tasks.JavaObjectsXmlFile.Import(String filename, JavaObjectsXmlFileReadType readType)
   at Xamarin.Android.Tasks.GenerateJavaCallableWrappers.GenerateWrappers(List`1 assemblies)
   at Xamarin.Android.Tasks.GenerateJavaCallableWrappers.RunTask()
   at Microsoft.Android.Build.Tasks.AndroidTask.Execute()

[jonathanpeppers]

I believe Java types require a package name, and that is what the error says?

Does this fix it:

[Register("literallyanyname.ViewName")]

[ray-geberit]

@jonathanpeppers Thanks. Yes, this fixed it.

So i guess before this package name was appended automatically by .Net for Android / Xamarin, cause only registering the ViewName worked since .Net for Android exisis and also for Xamarin. So i consider this as a Workaround and it would still be nice if the buid doesn't crash during compilation.

[jonathanpeppers]

I would not think this is anything to do with the move from Xamarin; it is the same codebase. Did you find a specific commit that suggested this?

The main thing to fix here would be to just make a real MSBuild error code instead of an exception.

[ray-geberit]

No, it has nothing to do with the move from Xamarin. I just said, that registering only the ViewName (without PackageName) already worked in Xamarin. It also worked in .Net for Android with previous .Net versions. If i set the TargetFramework to 'net7.0-android', 'net8.0-android' or 'net9.0-android', it would build fine. Just since TargetFramework 'net10.0-android' the exception appears.