如何从NDK(JNI)调用特定的Java方法? [英] How to invoke specific Java method from NDK(JNI)?

问题描述

我在这个话题上很新鲜.

I am fresh in this topic.

我在Android应用程序中使用NDK，而在Java中也有这种方法

I use NDK in my Android app and I have such method in Java

static byte[] getBytes(Bitmap bitmap)
{
    int size = bitmap.getRowBytes() * bitmap.getHeight();
    ByteBuffer byteBuffer = ByteBuffer.allocate(size);
    bitmap.copyPixelsToBuffer(byteBuffer);
    return byteBuffer.array();
}

现在我需要从NDK使用此方法

Now I need to use this method from NDK

实际上我写了这样的东西

Actually I wrote something like this

jbyteArray arr = env->CallStaticByteMethod(jniIds.helper_class, jniIds.get_bytes, image_obj);

但是问题是CallStaticByteMethod返回类型jbyte，但是我需要jbyteArray ...

But problem is CallStaticByteMethod return type jbyte, but I need jbyteArray...

那么，问如何编写此方法?

So, question how to write this method?

编辑

jobject arr_obj = env->CallStaticObjectMethod(jniIds.helper_class, jniIds.get_bytes, image_obj);
jbyteArray arr = static_cast<jbyteArray>(arr_obj);

//my needed result
unsigned char myArr = reinterpret_cast<unsigned char>(arr);

编辑

jbyteArray arr_obj = (jbyteArray) env->CallStaticObjectMethod(jniIds.helper_class, jniIds.get_bytes, image_obj);

现在我有jbyteArray ...但无论如何我不明白如何使用GetByteArrayElements将我的byte[]放入我的var unsigned char *i_image中?

Now I have jbyteArray... but anyway I don't understand how with using of GetByteArrayElements get my byte[] into my var unsigned char *i_image?

编辑

jbyteArray arr_obj = (jbyteArray)env->CallStaticObjectMethod(jniIds.helper_class, jniIds.get_bytes, image_obj);
jbyte *b = (jbyte *) env->GetByteArrayElements(arr_obj, NULL);
i_image = reinterpret_cast<unsigned char *>(b);
env->ReleaseByteArrayElements(arr_obj, b, JNI_ABORT);

推荐答案

根据

As per the JNI specification, byte arrays are not primitive types, they are objects. As such, you need to use CallStaticObjectMethod.

结果类型将为jobject，但是您可以安全地将其强制转换为jbyteArray(当然，如果不是null). 手持jbyteArray可以调用GetByteArrayElements或GetByteArrayRegion.

The result type will be jobject, but you can safely cast this to jbyteArray (if it is not null, of course). With the jbyteArray in hand you can call GetByteArrayElements or GetByteArrayRegion.

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