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kerams opened this issue Apr 26, 2025 · 9 comments · May be fixed by #10121
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Java.Lang.ClassNotFoundException: Didn't find class "<..>" on path: DexPathList #10081

kerams opened this issue Apr 26, 2025 · 9 comments · May be fixed by #10121
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@jonpryor @dellis1972 @jonathanpeppers
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Area: App+Library Build Issues when building Library projects or Application projects. need-attention A xamarin-android contributor needs to review
Milestone
.NET 10

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@kerams
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kerams commented Apr 26, 2025 •
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Android framework version

net10.0-android (Preview)

Affected platform version

10.0.100-preview.3.25201.16

Description

I'm inheriting from MediaDataSource in order to play audio in Android.Media.MediaPlayer from an in-memory mp3.

internal class StreamMediaDataSource(byte[] data) : Android.Media.MediaDataSource
{
    // ...
}

It worked just fine with 10.0.100-preview.2.25164.34, but with 10.0.100-preview.3.25201.16 I now get an exception during the instantiation of this class:

Java.Lang.ClassNotFoundException: Didn't find class "crc64467b05f37239e7a6.StreamMediaDataSource" on path: DexPathList[[directory "."],nativeLibraryDirectories=[/system/lib64, /system_ext/lib64, /system/lib64, /system_ext/lib64]]
   at Java.Interop.JniEnvironment.Types.TryFindClass(String classname, Boolean throwOnError)
   at Java.Interop.JniType..ctor(String classname)
   at Java.Interop.JniPeerMembers.JniInstanceMethods..ctor(Type declaringType)
   at Java.Interop.JniPeerMembers.JniInstanceMethods.GetConstructorsForType(Type declaringType)
   at Java.Interop.JniPeerMembers.JniInstanceMethods.StartCreateInstance(String constructorSignature, Type declaringType, JniArgumentValue* parameters)
   at Android.Media.MediaDataSource..ctor()
   at Plugin.Maui.Audio.StreamMediaDataSource..ctor(Byte[] data)
   at Plugin.Maui.Audio.AudioPlayer.Play(Byte[] data)

If I use global.json to pin the SDK to Preview 2, the problem disappears.

Steps to Reproduce

I failed to reproduce it in an empty project, so at the moment I'm in the dark with respect to what exactly might be the thing that makes a difference.
@kerams kerams added Area: App Runtime Issues in `libmonodroid.so`. needs-triage Issues that need to be assigned. labels Apr 26, 2025
@grendello grendello added Area: App+Library Build Issues when building Library projects or Application projects. and removed Area: App Runtime Issues in `libmonodroid.so`. needs-triage Issues that need to be assigned. labels Apr 28, 2025
@jonathanpeppers
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Can you share more of the code example on how StreamMediaDataSource is used? The top of the stacktrace shows Plugin.Maui.Audio.AudioPlayer.Play(Byte[] data), so can you share a more complete example? (sample app would be best)

Thanks!

@jonathanpeppers jonathanpeppers added the need-info Issues that need more information from the author. label Apr 28, 2025
@kerams
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kerams commented Apr 28, 2025 •
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This is the only call site, player is Android.Media.MediaPlayer.

public void Play(byte[] data)
{
	if (!(data?.Length > 0))
	{
		return;
	}

	player.Reset();
	player.SetDataSource(new StreamMediaDataSource(data));
	player.Prepare();
	player.Start();
	stopwatch.Restart();
	isPlaying = true;
}

This is located in a net10.0-android;net10.0-ios;net10.0 SingleProject assembly, in the same solution as the Avalonia Android entry project.

@dotnet-policy-service dotnet-policy-service bot added need-attention A xamarin-android contributor needs to review and removed need-info Issues that need more information from the author. labels Apr 28, 2025
@jonathanpeppers
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Is there some code in StreamMediaDataSource that sets up the byte[]?

@jonathanpeppers jonathanpeppers added this to the .NET 10 milestone Apr 28, 2025
@kerams
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kerams commented Apr 28, 2025

I'm not sure what that means exactly

internal class StreamMediaDataSource(byte[] data) : MediaDataSource
{
    public override long Size => data.Length;

    public override int ReadAt(long position, byte[]? buffer, int offset, int size)
    {
        if (position >= data.Length)
            return -1;

        var toRead = Math.Min(size, data.Length - (int)position);
        data.AsSpan((int)position, toRead).CopyTo(buffer.AsSpan(offset, toRead));
        return toRead;
    }

    public override void Close() { }
}

@jonathanpeppers
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I had some time to try to repro this, and I found Gerald has a sample using Plugin.Maui.Audio:

I found the "Stream Audio" button works fine on .NET 10 Preview 4 (unreleased nightly builds):

Image

Image

Is this sample similar enough to what you're doing here to cause the problem?

@jonathanpeppers jonathanpeppers added need-info Issues that need more information from the author. and removed need-attention A xamarin-android contributor needs to review labels May 5, 2025
@jonathanpeppers
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Here were my changes to target .NET 10:

@kerams
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kerams commented May 5, 2025

Thanks for looking into it. No, it's quite different. Mine is an Avalonia application where the shared and Android "shell" projects are F#. My modified version of Plugin.Maui.Audio is in the same solution and referenced by both projects. Guess I have no other choice but to start whittling the solution down until I have a small enough repro to share.

@dotnet-policy-service dotnet-policy-service bot added need-attention A xamarin-android contributor needs to review and removed need-info Issues that need more information from the author. labels May 5, 2025
@kerams
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kerams commented May 5, 2025 •
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Alright, here you go https://github.com/kerams/repro-and

When I run Mobile.Android in Debug in Pixel 7 Android 14 emulator, I see a toast message with the aforementioned exception after I press the play button.

When I switch to Preview 2, I get an expected error from the media player itself (input data is garbage).

jonpryor added a commit that referenced this issue May 7, 2025
@jonpryor
[NativeAOT] Provide the Android ClassLoader
661e265 
Fixes: #10081
Fixes: #10118

Context: 18ca528
Context: dotnet/java-interop@5852e6e

dotnet/java-interop@5852e6e3 updated `JniEnviroment.Types.FindClass()`
to begin using [`Class.forName(String, bool, ClassLoader)`][0] to load
Java types instead of `ClassLoader.loadClass()`.

This broke type registration on non-Java threads under NativeAOT;
attempting to load a non-Android Java type from a managed thread:

	var t = new System.Threading.Thread(() => {
	    using var c = new ClassFromThisAssembly();
	});
	t.Start();
	t.Join();

would fail with a `ClassNotFoundException`:

	E NUnit   : Java.Lang.ClassNotFoundException: Didn't find class "from.NewManagedThreadOne" on path: DexPathList[[directory "."],nativeLibraryDirectories=[/system/lib64, /system_ext/lib64, /system/lib64, /system_ext/lib64]]
	E NUnit   :    at Java.Interop.JniEnvironment.Types.TryFindClass(String, Boolean) + 0x3f4
	E NUnit   :    at Java.Interop.JniPeerMembers.JniInstanceMethods..ctor(Type) + 0x130
	E NUnit   :    at Java.Interop.JniPeerMembers.JniInstanceMethods.GetConstructorsForType(Type) + 0x94
	E NUnit   :    at Java.Interop.JniPeerMembers.JniInstanceMethods.StartCreateInstance(String, Type, JniArgumentValue*) + 0x1c
	E NUnit   :    at Java.Lang.Object..ctor() + 0x108
	E NUnit   :    at Java.InteropTests.JnienvTest.<>c__DisplayClass6_0.<RegisterTypeOnNewManagedThread>b__0() + 0x24
	E NUnit   :   --- End of managed Java.Lang.ClassNotFoundException stack trace ---
	E NUnit   : java.lang.ClassNotFoundException: Didn't find class "from.NewManagedThreadOne" on path: DexPathList[[directory "."],nativeLibraryDirectories=[/system/lib64, /system_ext/lib64, /system/lib64, /system_ext/lib64]]
	E NUnit   : 	at dalvik.system.BaseDexClassLoader.findClass(BaseDexClassLoader.java:259)
	E NUnit   : 	at java.lang.ClassLoader.loadClass(ClassLoader.java:637)
	E NUnit   : 	at java.lang.ClassLoader.loadClass(ClassLoader.java:573)

Fix this by setting `NativeAotRuntimeOptions.ClassLoader` to the
`context.getClassLoader()` value within
`NativeAotRuntimeProvider.attachInfo()`.  This ensures that we use
a `ClassLoader` that knows about the app's `classes.dex`.

[0]: https://developer.android.com/reference/java/lang/Class#forName(java.lang.String,%20boolean,%20java.lang.ClassLoader)
@jonpryor jonpryor linked a pull request May 7, 2025 that will close this issue
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@jonathanpeppers
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@kerams were you having this issue while using NativeAOT (PublishAot=true) or Mono (default settings)?

The sample looks like Mono:

If that's the case, #10121 won't fix this one.

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@dellis1972 dellis1972

@jonathanpeppers jonathanpeppers

Labels
Area: App+Library Build Issues when building Library projects or Application projects. need-attention A xamarin-android contributor needs to review
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[NativeAOT] Provide the Android ClassLoader dotnet/android
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@jonpryor @grendello @dellis1972 @jonathanpeppers @kerams