Question

I’m trying to send some data from c++ to java using JNI.

In c++ I have:

Array[0]:
string name = "myName"
int iterations = 16
float value = 15
... etc

So I want to use JNI to return all data on Java, I’m trying this, but don’t work

JNIEXPORT jobjectArray JNICALL Java_com_testing_data_MainActivity_getDATA(JNIEnv *env, jobject obj)
{
// 1º Create a temp object
jobject dataClass
    {
        jstring name;
                jint iterations;
                jfloat value;
    };


jobject tempObject = env->NewObject();

// Get data in c++ format int temp object type
std::vector<dataClass > data = getDataClass();  // First error, must be a c++ class, how could i get it?

// How much memory i need?
int dataSize = data.size();

// Reserve memory in java format
jint tempValues[dataSize];
jobjectArray tempArray = env->NewObjectArray(dataSize,dataClass,0); // 2º Error, it doesn 't create the class

    // Temporal store data in jarray
for (int i = 0; i < dataSize ; i++)
{
    tempArray[i].name = data[i].name;
            tempArray[i].iterations = data[i].iterations;
            tempArray[i].value = data[i].value;
}

return tempArray;   // return temp array

}

Are correct this steps to return a structure/object with data? How is possible to fix the errors?

Answer 1

Converting everything to JNI types is not a good idea. Generally, it is better to create a peer object, i.e. a handle pointer to the native resource – like the hWnd in the Windows GUI Programming.