Saratsin / DefaultInterfaceMemberIssue

Sample project with reproducible issue of java default interface members

Java interfaces with default members issue

Steps to reproduce

1. Run project with Min23 suffix
2. Look at app screen output

Expected result

"No error" is written as when you run project with Min24 suffix (the only difference between Min23 and Min24 projects is minSdkVersion in AndroidManifest.xml)

Actual Result

AbstractMethodError is thrown and shown in output

Conditions

1. Min SDK version for Xamarin.Android application is set to 23 or lower.
2. Binding library with java interface with default method implementation is connected to the project
3. C# class inherits from this java interface, default method is not implemented (thus, default implementation should be used)
4. C# class is casted to the interface and default method is called

Current workarounds for this issue

• Implement all default methods of the interface in C# class.
• Implement class in Java and bind it to C#, in this case default methods work properly
• Increase Min SDK version for Xamarin.Android application to 24 – then everything works like a charm

Possible reasons of this issue

Probably there's some issue with targetCompatibility/sourceCompatibility with Java 8. And it only relates to our custom C# classes which are inherited or implement some java classes/interfaces. When they exopose to Java world with java wrappers, probably something is going wrong. The big problem also is that this issue happens only in Runtime.