JniCpp11

An Easy way to write JNI code in C++11.

JniCpp11 ease the pain from writing the JNI boilerplate code, generates JNI type signatures, and handles reference management such as DeleteLocalRef and DeleteGlobalRef for you, etc.

Writing JNI code using JniCpp11 is almost as easy as writing their Java counter part, and less error prone. See Usage for details.

Installation

It is recommended that you use clang rather than gcc.

Cocos2d-x project

Clone this repo to cocos2d/external.

$ cd cocos2d/external
$ git submodule add <url-of-this-repo>

Then, add jnicpp11_static to LOCAL_STATIC_LIBRARIES and import its module in proj.android/jni/Android.mk.

# _COCOS_LIB_ANDROID_BEGIN
# ...
LOCAL_STATIC_LIBRARIES += jnicpp11_static
# _COCOS_LIB_ANDROID_END

# _COCOS_LIB_IMPORT_ANDROID_BEGIN
# ...
$(call import-module,JniCpp11)
# _COCOS_LIB_IMPORT_ANDROID_END

General JNI project

Just add JniCpp11.h and JniCpp11.cpp to your project. Then, set the JavaVM in JNI_OnLoad function like this:

jint JNI_OnLoad(JavaVM *vm, void *reserved) {
  Jni::setJvm(vm);
  return JNI_VERSION_1_4;
}

Usage

This README is still being written.

This project was initially created to remove dependencies on cocos2d-x from C++ wrappers of iOS/Android libraries. But now it can be used on more general JNI projects.

using namespace jnicpp11;

Finding a Java class

JniCpp11

{
  auto clazz = JavaClass::getClass("android/os/Debug");

  if (clazz) {
    // class found
  } else {
    // class not found
  }	
}
// at this scope, the underlying globalRef of clazz is already deleted

This returns a globalRef of the Java class. You can store it for future usage. If you don't, the globalRef automatically deleted as the variable goes out of scope.

Calling Java static methods

JniCpp11

// If the JNI call fails, 0 is returned
auto nativeHeapSize = clazz.staticCall<jlong>("getNativeHeapSize", 0);

// If the JNI call fails, "Unknown" is returned in this case
std::string arg1 = "....";
auto runTimeStats = clazz.staticCall<std::string>("statName", "Unknown", arg1);

// void method calls does not need to provide a default return value since it does not return any value
clazz.staticCallVoid("dumpHprofDataDdms");

Equivalent Java Code

import android.os.Debug;

long nativeHeapSize = Debug.getNativeHeapSize();

String arg1 = "...";
String runTimeStats = Debug.statName(arg1);

Debug.dumpHprofDataDdms();

Calling Java instance methods

Examples to be written.

Getting Java static fields

Examples to be written.

Getting Java instance fields

Examples to be written.