When targetting Android 11, binding a custom IComparator to Java.Util.Collections.Max throws a Couldn't bind to method ''. exception

[lwschan]

Steps to Reproduce

Application is working fine when targeting Android 10, when I update the target to Android 11, then this crash happens.

Stack trace

System.ArgumentException: Couldn't bind to method ''.
at System.Delegate.GetCandidateMethod (System.Type type, System.Type target, System.String method, System.Reflection.BindingFlags bflags, System.Boolean ignoreCase, System.Boolean throwOnBindFailure) [0x000e9] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/corlib/System/Delegate.cs:362   
at System.Delegate.CreateDelegate (System.Type type, System.Type target, System.String method, System.Boolean ignoreCase, System.Boolean throwOnBindFailure) [0x00014] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/corlib/System/Delegate.cs:375   at System.Delegate.CreateDelegate (System.Type type, System.Type target, System.String method) [0x00000] in /Users/builder/jenkins/workspace/archive-mono/2020-02/android/release/mcs/class/corlib/System/Delegate.cs:384   at Android.Runtime.AndroidTypeManager.RegisterNativeMembers (Java.Interop.JniType nativeClass, System.Type type, System.String methods) [0x0012e] in <227a96d68a0440cea172be41b1306654>:0   at Android.Runtime.JNIEnv.RegisterJniNatives (System.IntPtr typeName_ptr, System.Int32 typeName_len, System.IntPtr jniClass, System.IntPtr methods_ptr, System.Int32 methods_len) [0x00096] in <227a96d68a0440cea172be41b1306654>:0   at (wrapper managed-to-native) Java.Interop.NativeMethods.java_interop_jnienv_alloc_object(intptr,intptr&,intptr)  
at Java.Interop.JniEnvironment+Object.AllocObject (Java.Interop.JniObjectReference type) [0x00027] in <42748fcc36b74733af2d9940a8f3cc8e>:0   
at Java.Interop.JniType.AllocObject () [0x0000c] in <42748fcc36b74733af2d9940a8f3cc8e>:0   at Java.Interop.JniPeerMembers+JniInstanceMethods.StartCreateInstance (System.String constructorSignature, System.Type declaringType, Java.Interop.JniArgumentValue* parameters) [0x00044] in <42748fcc36b74733af2d9940a8f3cc8e>:0   at Java.Lang.Object..ctor () [0x00034] in <227a96d68a0440cea172be41b1306654>:0   at TimeLog.Mobile.Droid.Utilities.CompareSizesByArea..ctor () <0xad4c31e8 + 0x0002b> in <cc1cae8b0c4c44a9b7046b745060c8d6>:0   at TimeLog.Mobile.Droid.Activities.Expense.ImageSelectionActivity.SetUpCameraOutputs (System.Int32 width, System.Int32 height) [0x0007e] in C:\Users\Lewis\Documents\Projects\TimeLog.Mobility\TimeLog.Mobile\TimeLog.Mobile.Droid\Activities\Expense\ImageSelectionActivity.cs:861   at TimeLog.Mobile.Droid.Activities.Expense.ImageSelectionActivity.OpenCamera (System.Int32 width, System.Int32 height) [0x0004d] in C:\Users\Lewis\Documents\Projects\TimeLog.Mobility\TimeLog.Mobile\TimeLog.Mobile.Droid\Activities\Expense\ImageSelectionActivity.cs:321   
at TimeLog.Mobile.Droid.Listeners.Camera2BasicSurfaceTextureListener.OnSurfaceTextureAvailable (Android.Graphics.SurfaceTexture surface, System.Int32 width, System.Int32 height) [0x00001] in C:\Users\Lewis\Documents\Projects\TimeLog.Mobility\TimeLog.Mobile\TimeLog.Mobile.Droid\Listeners\Camera2BasicSurfaceTextureListener.cs:27   at Android.Views.TextureView+ISurfaceTextureListenerInvoker.n_OnSurfaceTextureAvailable_Landroid_graphics_SurfaceTexture_II (System.IntPtr jnienv, System.IntPtr native__this, System.IntPtr native_surface, System.Int32 width, System.Int32 height) [0x0000f] in <227a96d68a0440cea172be41b1306654>:0   at (wrapper dynamic-method) Android.Runtime.DynamicMethodNameCounter.100(intptr,intptr,intptr,int,int)

Code that generates the crash

var map = (StreamConfigurationMap)manager.GetCameraCharacteristics(cameraId).Get(CameraCharacteristics.ScalerStreamConfigurationMap);

if (map == null)
{
    continue;
}

// For still image captures, we use the largest available size.
var largest = (Size) Collections.Max(Arrays.AsList(map.GetOutputSizes((int) ImageFormatType.Jpeg)), new CompareSizesByArea());

The code crashes when trying to bind the CompareSizesByArea() as an IComparator for Collections.Max.

Code for CompareSizesByArea:

using Android.Util;
using Java.Lang;
using Java.Util;

namespace TimeLog.Mobile.Droid.Utilities
{
    public class CompareSizesByArea : Object, IComparator
    {
        #region Interface Implementations

        public int Compare(Object lhs, Object rhs)
        {
            var lhsSize = (Size) lhs;
            var rhsSize = (Size) rhs;

            // We cast here to ensure the multiplications won't overflow
            return Long.Signum((long) lhsSize.Width * lhsSize.Height - (long) rhsSize.Width * rhsSize.Height);
        }

        #endregion
    }
}

Expected Behavior

Application does not crash

Actual Behavior

Application crashes with System.ArgumentException: Couldn't bind to method ''.

Version Information

Microsoft Visual Studio Community 2019
Version 16.7.7
VisualStudio.16.Release/16.7.7+30621.155
Microsoft .NET Framework
Version 4.8.04084

Installed Version: Community

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Azure App Service Tools v3.0.0   16.7.532.28833
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[jpobst]

Full repo that exhibits the crash:

using Android.App;
using Android.OS;
using Android.Support.V7.App;
using Java.Util;
using Java.Lang;
using Android.Util;
using Android.Graphics;
using Android.Hardware.Camera2.Params;
using Android.Hardware.Camera2;
using Android.Content;
using System.Linq;

namespace App16
{
	[Activity (Label = "@string/app_name", Theme = "@style/AppTheme", MainLauncher = true)]
	public class MainActivity : AppCompatActivity
	{
		protected override void OnCreate (Bundle savedInstanceState)
		{
			base.OnCreate (savedInstanceState);

			// Set our view from the "main" layout resource
			SetContentView (Resource.Layout.activity_main);

			var manager = (CameraManager) GetSystemService (Context.CameraService);
			var id = manager.GetCameraIdList ().First ();
			var map = (StreamConfigurationMap) manager.GetCameraCharacteristics (id).Get (CameraCharacteristics.ScalerStreamConfigurationMap);

			// For still image captures, we use the largest available size.
			var largest = (Size) Collections.Max (Arrays.AsList (map.GetOutputSizes ((int) ImageFormatType.Jpeg)), new CompareSizesByArea ());
		}

		public class CompareSizesByArea : Object, IComparator
		{
			public int Compare (Object lhs, Object rhs)
			{
				var lhsSize = (Size) lhs;
				var rhsSize = (Size) rhs;

				// We cast here to ensure the multiplications won't overflow
				return Long.Signum ((long) lhsSize.Width * lhsSize.Height - (long) rhsSize.Width * rhsSize.Height);
			}
		}
	}
}

[jpobst]

I suspect this has to do with adding the static/default members to IComparator in API-30.

Here's IComparator in API-29:

namespace Java.Util
{
    [JavaTypeParameters(new string[] { "T" })]
    [Register("java/util/Comparator", "", "Java.Util.IComparatorInvoker")]
    public interface IComparator : IJavaObject, IDisposable, IJavaPeerable
    {
        [NullableContext(2)]
        [Register("compare", "(Ljava/lang/Object;Ljava/lang/Object;)I", "GetCompare_Ljava_lang_Object_Ljava_lang_Object_Handler:Java.Util.IComparatorInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null")]
        int Compare(Object o1, Object o2);

        [NullableContext(2)]
        [Register("equals", "(Ljava/lang/Object;)Z", "GetEquals_Ljava_lang_Object_Handler:Java.Util.IComparatorInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null")]
        bool Equals(Object obj);
    }
}

Here is part of it in API-30:

namespace Java.Util
{
    [JavaTypeParameters(new string[] { "T" })]
    [NullableContext(2)]
    [Register("java/util/Comparator", "", "Java.Util.IComparatorInvoker")]
    public interface IComparator : IJavaObject, IDisposable, IJavaPeerable
    {
        [Nullable(1)]
        private readonly static JniPeerMembers _members;

        private static Delegate cb_reversed;
        
        void .cctor()
        {
            IComparator._members = new XAPeerMembers("java/util/Comparator", typeof(IComparator), true);
        }

        [Register("compare", "(Ljava/lang/Object;Ljava/lang/Object;)I", "GetCompare_Ljava_lang_Object_Ljava_lang_Object_Handler:Java.Util.IComparatorInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null")]
        int Compare(Object o1, Object o2);

        [Register("equals", "(Ljava/lang/Object;)Z", "GetEquals_Ljava_lang_Object_Handler:Java.Util.IComparatorInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null")]
        bool Equals(Object obj);

        [NullableContext(1)]
        Delegate GetReversedHandler()
        {
            if (IComparator.cb_reversed == null)
            {
                IComparator.cb_reversed = JNINativeWrapper.CreateDelegate(new _JniMarshal_PP_L(IComparator.n_Reversed));
            }
            return IComparator.cb_reversed;
        }

        IntPtr n_Reversed(IntPtr jnienv, IntPtr native__this)
        {
            return JNIEnv.ToLocalJniHandle(Object.GetObject<IComparator>(jnienv, native__this, JniHandleOwnership.DoNotTransfer).Reversed());
        }

        [Register("reversed", "()Ljava/util/Comparator;", "GetReversedHandler:Java.Util.IComparator, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null", ApiSince=24)]
        IComparator Reversed()
        {
            unsafe
            {
                JniObjectReference jniObjectReference = IComparator._members.get_InstanceMethods().InvokeVirtualObjectMethod("reversed.()Ljava/util/Comparator;", this, 0);
                return Object.GetObject<IComparator>(jniObjectReference.get_Handle(), JniHandleOwnership.TransferLocalRef);
            }
        }
        
        // ... Other default/static methods removed for brevity ...
    }
}

I think the issue is that we are generating the invoking machinery for the regular methods in IComparatorInvoker, and the machinery for the static/default methods in IComparator. They likely all need to be in the same place.

[jonpryor]

Discussion starts at: https://discordapp.com/channels/732297728826277939/732297837953679412/773272111606399016

[jonpryor]

Of interest:

• More complete crash stack trace: https://gist.github.com/jpobst/c5cfe4af58fab7c9ec5f1d6fdebc6f06
  • How Object.AllocObject() can hit Delegate.CreateDelegate(): https://discordapp.com/channels/732297728826277939/732297837953679412/773290161214717962
• JCW output: https://gist.github.com/jpobst/3a883fbfcce61a8d43b9c587f8414910
• RegisterJniNatives(): https://github.com/xamarin/xamarin-android/blob/15b37758e9d65c82aebe1a327747b285f38ce791/src/Mono.Android/Android.Runtime/AndroidRuntime.cs#L394-L413

[lwschan]

Which Xamarin Android version will contain the fix for this issue?

[jpobst]

This fix should be available in VS 16.9 P2. (XA 11.2 P2)

[lwschan]

Thanks! @jpobst

[Depechie]

Is there any other workaround other than changing the API version or waiting for the 11.2 P2 release?