[Regression] .NET 10 Trimmer strips MediaElement constructors on Android despite preservation rules

[kizwiz6]

Is there an existing issue for this?

• I have searched the existing issues

Did you read the "Reporting a bug" section on Contributing file?

• I have read the "Reporting a bug" section on Contributing file: https://github.com/CommunityToolkit/Maui/blob/main/CONTRIBUTING.md#reporting-a-bug

Current Behavior

Since updating to .NET 10 (MAUI 10.0.41), applications using CommunityToolkit.Maui.MediaElement crash on Android when trimming is enabled. The trimmer is incorrectly identifying essential constructors and JNI-callback methods as unused code and stripping them.

Expected Behavior

The MauiMediaElement should survive the .NET 10 trimming process so that the Android OS can properly invoke its constructors during lifecycle events (like OnDetachedFromWindow or XAML inflation) without throwing a MissingMethodException.

Steps To Reproduce

1. Create a MAUI project targeting net10.0-android.
2. Add CommunityToolkit.Maui.MediaElement v8.0.0.
3. Configure the .csproj with the following aggressive trimming settings:

<PropertyGroup Condition="$(TargetFramework.Contains('-android'))">
    <AndroidLinkMode>Full</AndroidLinkMode>
    <PublishTrimmed>true</PublishTrimmed>
    <TrimMode>partial</TrimMode>
</PropertyGroup>

4. Navigate to a page containing a MediaElement.

Link to public reproduction project repository

https://github.com/kizwiz6/MauiBug

Environment

- .NET MAUI CommunityToolkit: 8.0.0
- OS: Windows 11
- .NET MAUI: 10.0.41
- Link Mode: Full
- Trim Mode: partial (Full trim mode causes even deeper XAML parser failures)

Anything else?

Crash Log Evidence:
The following stack trace was captured by wrapping InitializeComponent() in a diagnostic try-catch. It confirms the trimmer has removed the constructor:

=== TRIMMER CRASH DETECTED ===
Microsoft.Maui.Controls.Xaml.XamlParseException: Position 15:10. Arg_NoDefCTor, CommunityToolkit.Maui.Views.MediaElement
 ---> System.MissingMethodException: Arg_NoDefCTor, CommunityToolkit.Maui.Views.MediaElement
   at System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean wrapExceptions)
   at Microsoft.Maui.Controls.Xaml.CreateValuesVisitor.Visit(ElementNode node, INode parentNode)

Workarounds Attempted (and Failed):
In a separate and larger production project, the following attempts were made to preserve the types, but the .NET 10 trimmer ignored them:

• Added <TrimmerRootAssembly Include="CommunityToolkit.Maui.MediaElement" />
• Added explicit Linker.xml descriptors for the MauiMediaElement type.
• Added proguard.cfg rules.
  Result: The app still crashes with MissingMethodException (regarding Media3 listeners) or AbstractMethodError (regarding constructors).

[TheCodeTraveler]

Thanks! I confirmed this bug is also happening in our currently nightly build.

[ne0rrmatrix]

@kizwiz6 can you test #3116 and see if that PR fixes your issue?

[kizwiz6]

@ne0rrmatrix thanks for the quick turnaround. I tested PR #3116 and it has successfully resolved the initial MissingMethodException that occurred during XAML inflation - the app no longer crashes on navigating to the video page.

However, it still crashes on Android when navigating away (backing out) from the video page.

Crash Log:

Inner Exception: Unable to find a constructor with signature (Android.Content.Context) 
on type CommunityToolkit.Maui.Core.Views.MauiMediaElement. 
Please provide the missing constructor.
at Java.Interop.TypeManager.CreateProxy(Type, IntPtr, JniHandleOwnership)
at Android.Runtime.AndroidValueManager.CreatePeer(...)
at AndroidX.CoordinatorLayout.Widget.CoordinatorLayout.n_OnDetachedFromWindow(...)

Environment: .NET MAUI 10.0.41 | CommunityToolkit.Maui.MediaElement 8.0.0 | Android API 34

It looks like the (Android.Content.Context) constructor also needs a [DynamicDependency] attribute - Android's CoordinatorLayout invokes it during the OnDetachedFromWindow lifecycle event when the page is popped. Would it be possible to add a second [DynamicDependency] for that constructor alongside the existing one?

[ne0rrmatrix]

The PR has that set on both constructors already. I'll look into this further.

[kizwiz6]

Thanks. Just to add, in my production app, I actually already have an explicit Linker.xml descriptor set to preserve="all" for the MauiMediaElement type.

<linker>
  <assembly fullname="CommunityToolkit.Maui.MediaElement">
    <type fullname="CommunityToolkit.Maui.Core.Views.MauiMediaElement" preserve="all" />
  </assembly>
  <assembly fullname="CommunityToolkit.Maui.Core" preserve="all" />
</linker>

Despite this, and despite PR #3116 adding [DynamicDependency], the (Context) constructor is still being stripped in .NET 10.0.41 and the crash still occurs. It appears for me that the .NET 10 trimmer is ignoring both the attributes and the Linker.xml descriptors for JNI-invoked members during the Android lifecycle. So, that issue may be deeper than the [DynamicDependency] attributes.

[ne0rrmatrix]

@kizwiz6 Can you test latest PR update? I added more constructors and I decorated the OnDetachedFromWindow() method to see if that fixes it?

[kizwiz6]

@ne0rrmatrix Great news - I tested the latest update and the crash no longer occurs when navigating away from the video page in my production app. Both entering & exiting the video page now work correctly with trimming enabled on .NET 10.0.41 / Android API 34. Thank you so much!