Can't make call from C++ To Java using JNI

Question

I have a little project with cocos2d-x libraries. I'm trying to use C++ to call a Java function but i get a signal 11 exception at line:

// Get Status
status = jvm->GetEnv((void **) &env, JNI_VERSION_1_6);

But i don't know why this is happening.

In my Java class Getsocial.java exist this function:

private void tweet()
    {
        String score = "123";
        String tweetUrl = "https://twitter.com/intent/tweet?text=Hello ! I have just got " + score + " points in mygame for Android !!!!";
        Uri uri = Uri.parse(tweetUrl);
        startActivity(new Intent(Intent.ACTION_VIEW, uri));
    }

This function launch navigator to post a tweet. Called from Java works fine.

In my C++ InterfaceJNI.h I have:

#ifndef __INTERFACE_JNI_H__
#define __INTERFACE_JNI_H__

#include "cocos2d.h"

class InterfaceJNI
{
public:
    static void postMessageToFB();
    static void postMessageToTweet();

protected:

};

#endif // __INTERFACE_JNI_H__

And in InterfaceJNI.cpp:

#include "InterfaceJNI.h"
#include "platform/android/jni/JniHelper.h"
#include  jni.h >
#include  android/log.h >

using namespace cocos2d;

void InterfaceJNI::postMessageToTweet()
{
    int status;
    JNIEnv *env;
    JavaVM *jvm;
    jmethodID mid;
    jclass mClass;
    bool isAttached = false;

    CCLog("Static postMessageToTweet");

    // Get Status
    status = jvm->GetEnv((void **) &env, JNI_VERSION_1_6);

    CCLog("Status: %d", status);

    if(status AttachCurrentThread(&env, NULL);
        CCLog("Status 2: %d", status);
        if(status GetStaticMethodID(mClass, "tweet", "()V");
    CCLog("mID: %d", mid);

    if (mid!=0)
        env->CallStaticVoidMethod(mClass, mid);
            //-----------------------------------------------------------
    CCLog("Finish");
    if(isAttached)
        jvm->DetachCurrentThread();

    return;
}

This interface is called from a part of the code using:

#if (CC_TARGET_PLATFORM == CC_PLATFORM_ANDROID)
    InterfaceJNI::postMessageToTweet();
#elif (CC_TARGET_PLATFORM == CC_PLATFORM_IOS)
    ObjCCalls::trySendATweet();
#endif

What is happening to return a null pointer on jvm->GetEnv((void **) &env, JNI_VERSION_1_6); ?

Arita

Answer 1

It looks like your jvm variable is null or garbage. The version of Cocos2D-x I use has a class called JniHelper with a static ::getJavaVM(); method that you might want to use.

JavaVM* vm = JniHelper::getJavaVM();
JNIEnv* env;

vm->GetEnv((void**)&env,JNI_VERSION_1_4);  // mine uses JNI_VERSION_1_4

Also, remember to "refresh" your eclipse project every time you build with NDK. You probably do already, but it's worth checking.

Temper

This work fine to launch the function, now fail another with but thanks! – Arita