[regression/8.0.3] Android - Cannot create instance of type, no Java peer type found

[kernshen]

Description

Encountered this while upgrading my project to .Net Maui 8.

The error occurs when you have a class library with a class that derives from a base class inheriting from Java.Lang.Object in another class library.

Steps to Reproduce

1. Create a .NET Maui 8 class library with a base class inheriting from Java.Lang.Object
   MauiLib1

• BaseClass
• DerivedClass1 : No error when creating an instance

2. Create a .NET Maui 8 mobile app with a derived class of the base class in step 1.
   MauiApp1

• DerivedClass2 : No error when creating an instance

3. Create a .Net Maui 8 class library with a derived class of the base class in step 1.
   MauiLib2

• DerivedClass3

4. Create an instance of all 3 derived class in mobile app in step 2.
   Only System.NotSupportedException Message=Cannot create instance of type 'MauiLib2.DerivedClass3': no Java peer type found.

Link to public reproduction project repository

https://github.com/kernshen/NoJavaPeer.git

Version with bug

8.0.3

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

7.0.49

Affected platforms

Android

Affected platform versions

No response

Did you find any workaround?

Move derived class from class library to MauiApp project.

Relevant log output

Only System.NotSupportedException Message=Cannot create instance of type 'MauiLib2.DerivedClass3': no Java peer type found.

 at Java.Interop.JniPeerMembers.JniInstanceMethods..ctor(Type declaringType) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods.cs:line 22
   at Java.Interop.JniPeerMembers.JniInstanceMethods.GetConstructorsForType(Type declaringType) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods.cs:line 77
   at Java.Interop.JniPeerMembers.JniInstanceMethods.StartCreateInstance(String constructorSignature, Type declaringType, JniArgumentValue* parameters) in /Users/runner/work/1/s/xamarin-android/external/Java.Interop/src/Java.Interop/Java.Interop/JniPeerMembers.JniInstanceMethods.cs:line 139
   at Java.Lang.Object..ctor() in /Users/runner/work/1/s/xamarin-android/src/Mono.Android/obj/Release/net8.0/android-34/mcw/Java.Lang.Object.cs:line 37
   at MauiLib1.BaseClass..ctor()
   at MauiLib2.DerivedClass..ctor() in C:\Project\Maui\MauiApp1\MauiLib2\Platforms\Android\DerivedClass.cs:line 7
   at MauiApp1.App..ctor(IServiceProvider serviceProvider) in C:\Project\Maui\MauiApp1\MauiApp1\App.xaml.cs:line 18

[drasticactions]

Could you try reproducing this in a .NET Android app without the MAUI UI tooling? (dotnet new android)

This feels like something that would fail regardless of the MAUI UI Framework, if it fails in a .NET Android app then this should probably be moved to xamarin-android.

[ghost]

Hi @kernshen. We have added the "s/needs-info" label to this issue, which indicates that we have an open question for you before we can take further action. This issue will be closed automatically in 7 days if we do not hear back from you by then - please feel free to re-open it if you come back to this issue after that time.

[kernshen]

@drasticactions, indeed it fails in a .NET Android app (added to repos).

[drasticactions]

@jonathanpeppers Do you feel this is a xamarin-android issue? Could we please move it there if it is?

[Zhanglirong-Winnie]

Verified this issue with Visual Studio 17.10.0 Preview 1. Can repro on Android platform with sample project.
https://github.com/kernshen/NoJavaPeer.git

[jonathanpeppers]

As a workaround for this one, you can add a method that isn't called:

namespace MauiLib2
{
    public class DerivedClass3 : BaseClass
    {
        static Type FixMe() => typeof(Android.Views.View);

This causes MauiLib2.dll to have a reference to Mono.Android.dll and everything works.