Problem with Android.Graphics.Paint.Color property marshalers

[radekdoulik]

The new marshalers we generate are incompatible with the old ones. They use different types. The original ones work with int, while the new ones use Android.Graphics.Color. That means that we return proxy object from the property getter.

The old code:

using Android.Runtime;
using System;

private static Delegate GetGetColorHandler ()
{
	if (Paint.cb_getColor == null) {
		Paint.cb_getColor = JNINativeWrapper.CreateDelegate (new Func<IntPtr, IntPtr, int> (Paint.n_GetColor));
	}
	return Paint.cb_getColor;
}

using Android.Runtime;
using Java.Lang;
using System;

private static int n_GetColor (IntPtr jnienv, IntPtr native__this)
{
	Paint @object = Java.Lang.Object.GetObject<Paint> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
	return @object.Color.ToArgb ();
}

The new marshaler:

using Android.Graphics;
using Java.Interop;
using System;
using System.Reflection;

public static IntPtr n_getColor (IntPtr __jnienv, IntPtr __this)
{
	JniTransition jniTransition = new JniTransition (__jnienv);
	JniRuntime runtime = default(JniRuntime);
	Color color = default(Color);
	Java.Interop.ProxyValueMarshaler proxyValueMarshaler = default(Java.Interop.ProxyValueMarshaler);
	JniValueMarshalerState jniValueMarshalerState = default(JniValueMarshalerState);
	try {
		runtime = JniEnvironment.Runtime;
		JniRuntime.JniValueManager valueManager = runtime.ValueManager;
		valueManager.WaitForGCBridgeProcessing ();
		MyPaint value = valueManager.GetValue<MyPaint> (__this);
		color = value.Color;
		proxyValueMarshaler = new Java.Interop.ProxyValueMarshaler ();
		jniValueMarshalerState = proxyValueMarshaler.CreateArgumentState (color, ParameterAttributes.None);
		IntPtr handle = jniValueMarshalerState.ReferenceValue.Handle;
		return JniEnvironment.References.NewReturnToJniRef (jniValueMarshalerState.ReferenceValue);
		IL_006b:;
	} catch (Exception ex) when (runtime.ExceptionShouldTransitionToJni (ex)) {
		jniTransition.SetPendingException (ex);
		return default(IntPtr);
		IL_00a9:;
	} finally {
		proxyValueMarshaler.DestroyArgumentState (color, ref jniValueMarshalerState, ParameterAttributes.None);
		jniTransition.Dispose ();
	}
	IntPtr intPtr = default(IntPtr);
	return intPtr;
}

There's also an issue with destroying the state in finally block.

[radekdoulik]

I wonder how that could have worked before. The https://jenkins.mono-project.com/job/xamarin-android-pr-builder/4177 was green not so long ago.

[jonpryor]

I don't know why it worked before. Unfortunately, we don't upload test-related artifacts to Azure. :-(

I do know what the "problem" is: Android.Graphics.Color needs a "custom value marshaler," a'la: https://github.com/xamarin/java.interop/blob/23372eafa446baf93d80e14a58866d75ad557d26/src/Java.Interop.Export/Tests/Java.Interop/ExportTest.cs#L110-L152

That way, Android.Graphics.Color marshaling can be as IL-efficient as what generator currently emits, without jnimarshalmethod-gen.exe needing to know anything specific about Android.Graphicsc.Color.