从JNI/NDK返回从C到Java的2D原始数组

Question

我已经找到了大量关于如何在JNI中生成2D原始数组并将其返回给Java的文档.但是这些信息无法描述如何在C中给出上下文传递已经存在的 2D浮点数组(float**).

为了明确地描述我的问题,我将添加一些我想要实现的C伪代码:

// Returns a 2D float array from C to Java
jfloatArray ndk_test_getMy2DArray(JNIEnv* env, jobject thiz, jlong context)
{
    // Cast my context reference
    MyContextRef contextRef = (MyContextRef) context;

    // In case we need it below
    unsigned int length = MyContextGet1DLength(contextRef);

    // Get the 2D Array we want to "Cast"
    float** primitive2DArray = MyContextGet2DArray(contextRef);

    // Hokus pokus...
    // We do something to create the returnable data to Java
    //
    // Below is the missing piece that would convert the primitive
    // 2D array into something that can be returned consumed and consumed
    // by Java

    jfloatArray myReturnable2DArray

    return myReturnable2DArray;
}

我假设这不是直截了当的,因为我无法找到描述这种情况的任何内容.

感谢您提供有用的信息.

Answer 1

感谢Timo的帮助和链接.对于后人,我正在添加一个完整的代码集,该代码集将通过Java从现有的C 2D原始数组生成可以使用的2D原始数组.

// Returns a 2D float array from C to Java
jobjectArray ndk_test_getMy2DArray(JNIEnv* env, jobject thiz, jlong context)
{
    // Cast my context reference
    MyContextRef contextRef = (MyContextRef) context;

    // Get the length for the first and second dimensions
    unsigned int length1D = MyContextGet1DLength(contextRef);
    unsigned int length2D = MyContextGet2DLength(contextRef);

    // Get the 2D float array we want to "Cast"
    float** primitive2DArray = MyContextGet2DArray(contextRef);

    // Get the float array class
    jclass floatArrayClass = (*env)->FindClass(env, "[F");

    // Check if we properly got the float array class
    if (floatArrayClass == NULL)
    {
        // Ooops
        return NULL;
    }

    // Create the returnable 2D array
    jobjectArray myReturnable2DArray = (*env)->NewObjectArray(env, (jsize) length1D, floatArrayClass, NULL);

    // Go through the firs dimension and add the second dimension arrays
    for (unsigned int i = 0; i < length1D; i++)
    {
        jfloatArray floatArray = (*env)->NewFloatArray(env, length2D);
        (*env)->SetFloatArrayRegion(env, floatArray, (jsize) 0, (jsize) length2D, (jfloat*) primitive2DArray[i]);
        (*env)->SetObjectArrayElement(env, myReturnable2DArray, (jsize) i, floatArray);
        (*env)->DeleteLocalRef(env, floatArray);
    }

    // Return a Java consumable 2D float array
    return myReturnable2DArray;
}