Issue 1848 - Clean up local reference handling

jni/JniEventCallback.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2015 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 22 matching lines @@
 
 JniEventCallback::JniEventCallback(JNIEnv* env, jobject callbackObject)
   : JniCallbackBase(env, callbackObject)
 {
 }
 
 void JniEventCallback::Callback(AdblockPlus::JsValueList& params)
 {
   JNIEnvAcquire env(GetJavaVM());
 
-  jclass clazz = env->GetObjectClass(GetCallbackObject());
-  jmethodID method = env->GetMethodID(clazz, "eventCallback", "(Ljava/util/List;)V");
+  jmethodID method = env->GetMethodID(
+      *JniLocalReference<jclass>(*env,

[Felix Dahlke, 2015/02/03 05:22:50]

I think I've seen at least three instances of pretty much this code - have you
thought about returning a JniLocalReference<jclass> from something like
JniCallbackBase::GetCallbackClass()?

[René Jeschke, 2015/02/03 13:51:26]

Yeah, the first implementation supported this, but not this here because I do
not have a copy constructor. Implementing a copy constructor would also mean
implementing reference counting, which I thought of as a little bit of
over-engineering.

So, we should leave it like it is.

[Felix Dahlke, 2015/02/04 04:11:50]

Good point, yeah.

+          env->GetObjectClass(GetCallbackObject())),
+      "eventCallback", "(Ljava/util/List;)V");
 
   if (method)
   {
     jobject jsList = JniJsValueListToArrayList(*env, params);
     env->CallVoidMethod(GetCallbackObject(), method, jsList);
   }
 }
 
 static JNINativeMethod methods[] =
 {
   { (char*)"ctor", (char*)"(Ljava/lang/Object;)J", (void*)JniCtor },
   { (char*)"dtor", (char*)"(J)V", (void*)JniDtor }
 };
 
 extern "C" JNIEXPORT void JNICALL Java_org_adblockplus_libadblockplus_EventCallback_registerNatives(JNIEnv *env, jclass clazz)
 {
   env->RegisterNatives(clazz, methods, sizeof(methods) / sizeof(methods[0]));
 }