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Add proper MSBuild error XA4238 for JCW XML import failures #10717

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Add proper MSBuild error XA4238 for JCW XML import failures #10717

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Copilot AI commented Jan 23, 2026 •
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  • Analyze the issue and understand the problem
  • Review the stack trace and identify where the error occurs
  • Understand the existing error handling patterns in the codebase
  • Add try-catch handling in GenerateJavaCallableWrappers.GenerateWrappers() to catch InvalidOperationException
  • Create a proper MSBuild error with error code XA4238 for the exception
  • Add a new error resource string for the error (XA4238)
  • Add test for XA4238 error scenario (InvalidConfigTests.cs)
  • Request code review - PASSED

Summary

This PR fixes issue #10715 by converting the unhandled InvalidOperationException that occurs when using [Register("CustomView")] without a package prefix into a proper MSBuild error (XA4238).

Changes Made:

  1. src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaCallableWrappers.cs - Added try-catch around JavaObjectsXmlFile.Import() to catch InvalidOperationException and log a proper MSBuild error
  2. src/Xamarin.Android.Build.Tasks/Properties/Resources.resx - Added new error message XA4238
  3. src/Xamarin.Android.Build.Tasks/Properties/Resources.Designer.cs - Added generated code for XA4238
  4. src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/InvalidConfigTests.cs - Added test for XA4238 that creates a View with [Register("CustomView")] and asserts the error is emitted

Error Message:

Before: System.InvalidOperationException: Missing required attribute 'package' (stack trace)
After: error XA4238: Could not load Java callable wrapper XML file '{path}': Missing required attribute 'package'

Original prompt

This section details on the original issue you should resolve

<issue_title>Register Attribute breaks build</issue_title>
<issue_description>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.

Image

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()
```</issue_description>

<agent_instructions>Try to figure out what actually broke this in .NET 10. Review git history to discover what went wrong.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@jonathanpeppers</author><body>
I believe Java types require a package name, and that is what the error says?

Does this fix it:
```csharp
[Register("literallyanyname.ViewName")]
```</body></comment_new>
<comment_new><author>@jonathanpeppers</author><body>
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.</body></comment_new>
</comments>

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@jonathanpeppers
Add proper MSBuild error (XA4238) for JCW XML import failures
264f73e 
Co-authored-by: jonathanpeppers <840039+jonathanpeppers@users.noreply.github.com>
Copilot AI changed the title [WIP] Fix build issue caused by Register attribute in custom view Add proper MSBuild error XA4238 for JCW XML import failures Jan 23, 2026
Copilot AI requested a review from jonathanpeppers January 23, 2026 20:13
jonathanpeppers
jonathanpeppers reviewed Jan 23, 2026
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@copilot can you add a test for this scenario and assert it gets XA4238

jonathanpeppers
jonathanpeppers requested changes Jan 23, 2026
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We should not merge, as I understand now a fix is required in dotnet/java-interop.

Copilot AI mentioned this pull request Jan 23, 2026
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@jonathanpeppers
Add test for XA4238 error when Register attribute has no package
25c088a 
Co-authored-by: jonathanpeppers <840039+jonathanpeppers@users.noreply.github.com>
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Copilot AI commented Jan 23, 2026

@copilot can you add a test for this scenario and assert it gets XA4238

Added test in InvalidConfigTests.XA4238() that creates a custom View with [Register("CustomView")] (no package prefix) and asserts the build fails with XA4238 error. (25c088a)

Copilot AI requested a review from jonathanpeppers January 23, 2026 20:50
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@jonathanpeppers jonathanpeppers Awaiting requested review from jonathanpeppers jonathanpeppers is a code owner

@grendello grendello Awaiting requested review from grendello grendello will be requested when the pull request is marked ready for review grendello is a code owner

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Register Attribute breaks build

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