使用JNI将图像从Java传递到C ++

Question

I am using NDK and JNI for my android app therefore I have some of my codes in native. I have a custom adapter in which there's a list view that displays the images and buttons, that came from a database btw. However, the image will be used by the c++. If I click the button (from the java code), it will pass (I really don't know the term) the image to the c++ code where I will use the image. Is it possible for the c++ code to access the image triggered by the button from the Java code?

I'm pretty much a beginner but this is for my final project so any help will be appreciated :)

Adapter.Java

@Override
public View getView(int position, View convertView, ViewGroup parent) {

    View v = View.inflate(mContext, R.layout.listview, null);
    TextView pName = (TextView) v.findViewById(R.id.product_name);
    ImageView pImage = (ImageView) v.findViewById(R.id.product_image);
    TextView pPrice = (TextView) v.findViewById(R.id.product_price);
    TextView pDescription = (TextView) v.findViewById(R.id.product_description);
    TextView pCategory = (TextView) v.findViewById(R.id.product_category);
    pName.setText(mProductList.get(position).getName());

    Product image = mProductList.get(position);
    final byte[] img = image.getImage();
    Bitmap bitmap = BitmapFactory.decodeByteArray(img, 0, img.length);
    pImage.setImageBitmap(bitmap);

    pPrice.setText("$" + String.valueOf(mProductList.get(position).getPrice()));
    pDescription.setText(mProductList.get(position).getDescription());
    pCategory.setText(mProductList.get(position).getCategory());

    Button tryMe = (Button)v.findViewById(R.id.tryMe);
    tryMe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent cameraIntent = new Intent(mContext, OpencvCamera.class);
            mContext.startActivity(cameraIntent);
        }
    });

    return v;
}

This code below is where I want my button to pass the image from the database to the c++ in which it will be used with the camera. In here, the button only redirects when pressed to the camera class.

    Button tryMe = (Button)v.findViewById(R.id.tryMe);
    tryMe.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            /*WHAT SHOULD I PUT HERE FOR THE IMAGE PASSING*/

            Intent cameraIntent = new Intent(mContext, OpencvCamera.class);
            mContext.startActivity(cameraIntent);
        }
    }

Below are the codes for my C++

JNIEXPORT void JNICALL Java_nerds_thesis_clartips_OpencvClass_humanDetection
  (JNIEnv *, jclass, jlong addrRgba){
    Mat& frame = *(Mat*)addrRgba;

    detectHuman(frame);
    }  

   void detectHuman(Mat& frame){
      String human_cascade_name = "/storage/emulated/0/haarcascade_upperbody.xml";
      CascadeClassifier human_cascade;
      if(!human_cascade.load( human_cascade_name ) ) { printf("--(!)Error loading\n"); return; };
      std::vector<Rect> humans;
      Mat frame_gray;
      cvtColor( frame, frame_gray, CV_BGR2GRAY );
      equalizeHist( frame_gray, frame_gray);

      //Detect Human
      human_cascade.detectMultiScale( frame_gray, humans, 1.1, 2, 0 | CV_HAAR_SCALE_IMAGE, Size(100, 100) );
      Mat imageMask = imread("/storage/emulated/0/plain.png");

      /*CODE FOR OVERLAYING THE IMAGE TO THE CAMERA*/

The line above Mat imageMask = imread("/storage/emulated/0/plain.png"); is what I only do for testing. I only declared it and any of my buttons used the same image. Of course it will. That's why I'm asking what should I do to have my native code get an access with the images when I press the button created with a java code.

Answer 1

I don't think it is possible to pass the image object in memory; however you can pass a reference to the image, like an URI or filepath for your C++ code to use. Simply adapt your JNI declaration to add that reference.