Java call native with callback of anonymous inner class

• Lib.kt

  package com.practice
  
  class Lib {
  
      external fun getJniVersion(callback: Callback)
  
      interface Callback {
          fun onResponse(version: String)
      }
  
      init {
          System.loadLibrary("native-lib")
      }
  }
  

• CMakeLists.txt

  cmake_minimum_required(VERSION 3.10.2)
  
  add_library(native-lib SHARED native-lib.cpp)
  
  find_library(log-lib log)
  
  target_link_libraries(native-lib ${log-lib})
  

• native-lib.cpp

  #include <jni.h>
  #include <android/log.h>
  
  jstring getVersion(JNIEnv *env) {
      switch (env->GetVersion()) {
          case JNI_VERSION_1_1:
              return env->NewStringUTF("JNI_VERSION_1_1");
          case JNI_VERSION_1_2:
              return env->NewStringUTF("JNI_VERSION_1_2");
          case JNI_VERSION_1_4:
              return env->NewStringUTF("JNI_VERSION_1_4");
          case JNI_VERSION_1_6:
              return env->NewStringUTF("JNI_VERSION_1_6");
          default:
              return env->NewStringUTF("UNKNOWN");
      }
  }
  
  extern "C" JNIEXPORT void JNICALL
  Java_com_practice_Lib_getJniVersion(JNIEnv *env, jobject /* this */, jobject callback) {
      __android_log_print(ANDROID_LOG_DEBUG, "native", "looking for class");
      jclass callbackClass = env->GetObjectClass(callback);
      if (callbackClass != nullptr) {
          jmethodID methodId = env->GetMethodID(callbackClass, "onResponse", "(Ljava/lang/String;)V");
          if (methodId != nullptr) {
              env->CallVoidMethod(callback, methodId, getVersion(env));
          } else {
              __android_log_print(ANDROID_LOG_DEBUG, "native", "can not find method");
          }
      } else {
          __android_log_print(ANDROID_LOG_DEBUG, "native", "can not find class");
      }
  }
  

• MainActivity.kt

  package com.practice
  
  import androidx.appcompat.app.AppCompatActivity
  import android.os.Bundle
  import kotlinx.android.synthetic.main.activity_main.*
  
  class MainActivity : AppCompatActivity() {
  
      override fun onCreate(savedInstanceState: Bundle?) {
          super.onCreate(savedInstanceState)
          setContentView(R.layout.activity_main)
  
          Lib().getJniVersion(object : Lib.Callback {
              override fun onResponse(version: String) {
                  sample_text.text = version
              }
          })
      }
  
  }
  

use of deleted global reference error

When I call the Java method with wrong parameter type such as:

env->CallVoidMethod(callback, methodId, "jni version");

I will get below error:

JNI DETECTED ERROR IN APPLICATION: use of deleted global reference

Can't succeed in calling a Java function from a C++ module with JNI

illegal class name error

When I find class with wrong format jclass callbackClass = env->FindClass("com/practice/Lib.Callback");, I will get error.

A/art: art/runtime/java_vm_ext.cc:410] JNI DETECTED ERROR IN APPLICATION: illegal class name 'com/practice/Lib.Callback'
A/art: art/runtime/java_vm_ext.cc:410]     (should be of the form 'package/Class', [Lpackage/Class;' or '[[B')
A/art: art/runtime/java_vm_ext.cc:410]     in call to FindClass
A/art: art/runtime/java_vm_ext.cc:410]     from void com.practice.Lib.getJniVersion(com.practice.Lib$Callback)

It should be env->FindClass("com/practice/Lib$Callback") for inner class.