JNI使用Android 5+将参数传递回Java

Question

I am having this native code to get back an array of shorts :)

extern "C" 
JNIEXPORT jshortArray Java_my_application_CallerClazz_getShortArray(JNIEnv *jenv, jobject self)
{
    jshortArray shortArray = jenv->NewShortArray(size);
    jshort* p2ji = jenv->GetShortArrayElements(shortArray, JNI_FALSE);
    for(int idx = 0; idx < size; idx++)
    {
        p2ji[idx] = srcArray[idx];
    }
    return shortArray;
}

It works fine with all Android versions < 5. Since Android 5 the native code itself works fine, but the short[] on the java side is filled just with 0 .

Anybody has a tip why this happens?

Answer 1

Quoting from the JNI documentation for Get<PrimitiveType>ArrayElements() :

Since the returned array may be a copy of the Java array, changes made to the returned array will not necessarily be reflected in the original array until Release<PrimitiveType>ArrayElements() is called.

So before returning from your C++ function you should call RelaseShortArrayElements with mode == 0 ( 0 means "copy back the content and free the elems buffer" ).