env->FindClass function returns null

Question

I am trying to call some functions in my java class from my cpp class. I am succesful in making these calls thrice until i call a function 4th time. I am using cocos2dx engine.

I call function in MiscManager.java from MiscManagerJni.cpp

I get the following error when i try to get classID and game crashes:

12-20 12:06:09.328: W/System.err(26651): java.lang.NoClassDefFoundError: [generic] 12-20 12:06:09.328: W/System.err(26651): at dalvik.system.NativeStart.main(Native Method) 12-20 08:56:35.402: D/libMiscManager(25952): Failed to find class of com/games/Game/MiscManager

I have successfully called functions 3 times in MiscManager.java class from MiscManagerJni.cpp class. But the 4th time null is returned when i call

jclass ret = pEnv->FindClass(CLASS_NAME);

Can anyone tell me what is causing this error.

These are the functions i am using to get method id and class id

#define  LOG_TAG    "libMiscManager"
#define  LOGD(...)  __android_log_print(ANDROID_LOG_DEBUG,LOG_TAG,__VA_ARGS__)
#define  CLASS_NAME "com/games/Game/MiscManager"

typedef struct JniMethodInfo_
{
    JNIEnv *    env;
    jclass      classID;
    jmethodID   methodID;
}   JniMethodInfo;


extern "C"

{
    // get env and cache it
    static JNIEnv* getJNIEnv(void)
    {

    JavaVM* jvm = cocos2d::JniHelper::getJavaVM();
    if (NULL == jvm) {
        LOGD("Failed to get JNIEnv. JniHelper::getJavaVM() is NULL");
        return NULL;
    }

    JNIEnv *env = NULL;
    // get jni environment
    jint ret = jvm->GetEnv((void**)&env, JNI_VERSION_1_4);

    switch (ret) {
        case JNI_OK :
            // Success!

            return env;

        case JNI_EDETACHED :
            // Thread not attached
            if (jvm->AttachCurrentThread(&env, NULL) < 0)
            {
                LOGD("Failed to get the environment using AttachCurrentThread()");
                return NULL;
            } else {
                // Success : Attached and obtained JNIEnv!
                return env;
            }

        case JNI_EVERSION :

            // Cannot recover from this error
            LOGD("JNI interface version 1.4 not supported");
        default :

            LOGD("Failed to get the environment using GetEnv()");
            return NULL;
    }
}

// get class and make it a global reference, release it at endJni().
static jclass getClassID(JNIEnv *pEnv)
{
    jclass ret = pEnv->FindClass(CLASS_NAME);
    if (! ret)
    {
        LOGD("Failed to find class of %s", CLASS_NAME);
    }
    return ret;
}

static bool getStaticMethodInfo(cocos2d::JniMethodInfo &methodinfo, const char *methodName, const char *paramCode)
{
    jmethodID methodID = 0;
    JNIEnv *pEnv = 0;
    bool bRet = false;

    do 
    {
        pEnv = getJNIEnv();
        if (! pEnv)
        {
            break;
        }

        jclass classID = getClassID(pEnv);

        methodID = pEnv->GetStaticMethodID(classID, methodName, paramCode);

        if (! methodID)
        {
            LOGD("Failed to find static method id of %s", methodName);
            break;
        }
        methodinfo.classID = classID;
        methodinfo.env = pEnv;
        methodinfo.methodID = methodID;

        bRet = true;
    } while (0);
    return bRet;


   }

 void InitJni()
      {
        cocos2d::JniMethodInfo methodInfo;
        if (! getStaticMethodInfo(methodInfo, "Init", "()V"))
        {
            return ;
        }

    methodInfo.env->CallStaticVoidMethod(methodInfo.classID, methodInfo.methodID);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);
}

void SaveBooleanJni(const char *key, bool value)
    {
         cocos2d::JniMethodInfo methodInfo;
        if (! getStaticMethodInfo(methodInfo, "SaveBoolean", "(Ljava/lang/String;Z)V"))
        {
        return;
    }

    jstring stringArg = methodInfo.env->NewStringUTF(key);
    methodInfo.env->CallStaticVoidMethod(methodInfo.classID, methodInfo.methodID, stringArg, value);
    methodInfo.env->DeleteLocalRef(stringArg);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);
}

void SaveIntegerJni(const char *key, int value)
{
    cocos2d::JniMethodInfo methodInfo;
    if (! getStaticMethodInfo(methodInfo, "SaveInteger", "(Ljava/lang/String;I)V"))
    {
        return;
    }

    jstring stringArg = methodInfo.env->NewStringUTF(key);
    methodInfo.env->CallStaticVoidMethod(methodInfo.classID, methodInfo.methodID, stringArg, value);
    methodInfo.env->DeleteLocalRef(stringArg);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);
}

void SaveLongJni(const char *key, long value)
{
    cocos2d::JniMethodInfo methodInfo;
    if (! getStaticMethodInfo(methodInfo, "SaveLong", "(Ljava/lang/String;J)V"))
    {
        return;
    }
    jstring stringArg = methodInfo.env->NewStringUTF(key);
    methodInfo.env->CallStaticVoidMethod(methodInfo.classID, methodInfo.methodID, stringArg, value);
    methodInfo.env->DeleteLocalRef(stringArg);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);
}

long GetLongJni(const char *key, long defaultValue)
{
     cocos2d::JniMethodInfo methodInfo;
    long ret = 0;
    if (! getStaticMethodInfo(methodInfo, "GetInteger", "(Ljava/lang/String;J)J"))
    {
        return ret;
    }

    jstring stringArg = methodInfo.env->NewStringUTF(key);
    ret = methodInfo.env->CallStaticLongMethod(methodInfo.classID, methodInfo.methodID, stringArg, defaultValue);
    methodInfo.env->DeleteLocalRef(stringArg);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);

    return (long)ret;
}

bool GetBooleanJni(const char *key, bool defaultValue)
{
     cocos2d::JniMethodInfo methodInfo;
    jboolean ret = false;
    if (! getStaticMethodInfo(methodInfo, "GetBoolean", "(Ljava/lang/String;Z)Z"))
    {
        return ret;
    }
     jstring stringArg = methodInfo.env->NewStringUTF(key);
    ret = methodInfo.env->CallStaticIntMethod(methodInfo.classID, methodInfo.methodID, stringArg, defaultValue);
    methodInfo.env->DeleteLocalRef(stringArg);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);

    return ret;
}

int GetIntegerJni(const char *key, int defaultValue)
{
    cocos2d::JniMethodInfo methodInfo;
    int ret = 0;
    if (! getStaticMethodInfo(methodInfo, "GetInteger", "(Ljava/lang/String;I)I"))
    {
        return ret;
    }

    jstring stringArg = methodInfo.env->NewStringUTF(key);
    ret = methodInfo.env->CallStaticIntMethod(methodInfo.classID, methodInfo.methodID, stringArg, defaultValue);
    methodInfo.env->DeleteLocalRef(stringArg);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);

    return (unsigned int)ret;
}

bool IsConnectedToNetworkJni()
{
    cocos2d::JniMethodInfo methodInfo;
    jboolean ret = false;
    if (! getStaticMethodInfo(methodInfo, "IsConnectedToNetwork", "()Z"))
    {
        return ret;
    }

    ret = methodInfo.env->CallStaticBooleanMethod(methodInfo.classID, methodInfo.methodID);
    methodInfo.env->DeleteLocalRef(methodInfo.classID);

    return ret;
}
}

Answer 1

I solved the problem by using JNIHelper class in cocos2dx engine. I used getStaticMethodInfo in JNIHelper class instead of writing in my own class.