JNI access object array from C error

Question

I have an android project that uses a c++ library and i need to send an object array to the c++ code.

This is my Java native bind code

class MyLib {
    public static native void testArray(String[] array);
}

This is how i call it

...
MyLib.testArray(new Object[20]);
...

And this is my c++ jni code:

JNIEXPORT void JNICALL Java_com_android_mypackage_MyLib_testArray(JNIEnv * env, jobjectArray arr) {
    __android_log_print(ANDROID_LOG_INFO,"test","test array!!!!!!!!");
    int count = env->GetArrayLength(arr);
    __android_log_print(ANDROID_LOG_INFO,"test","array length %d", count);
     for (int i=0; i<count; i++) {
        __android_log_print(ANDROID_LOG_INFO,"test","--- get item %d", i);
        jstring jkey    = (jstring) env->GetObjectArrayElement(arr, i);
        __android_log_print(ANDROID_LOG_INFO,"test","item %d", i);    
        env->DeleteLocalRef(jkey);
    }
}

When i execute that, logcat shows this and execution ends with sigsev 11

JNI WARNING: jarray arg has wrong type (expected array, got Ljava/lang/Class;) in Lcom/android/mypackage/MyLib;.testArray:([Ljava/lang/Object;)V (GetArrayLength)

Any ideas why my array reference appears to be a class reference? I have no problems with arrays of native types, only with objects.

wojtek.kalicinski · Accepted Answer · 2013-09-12 18:38:24Z

5

I believe your function signature

JNIEXPORT void JNICALL Java_com_android_mypackage_MyLib_testArray(JNIEnv * env, jobjectArray arr)

should look like this:

JNIEXPORT void JNICALL Java_com_android_mypackage_MyLib_testArray(JNIEnv * env, jclass clazz, jobjectArray arr)

You're missing the second parameter - which in static methods is always the Class object.

answered Sep 12, 2013 at 18:38

wojtek.kalicinski

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