Android change image in a ImageView?

Question

I have a picture as a resource, that I need to modify thanks to OpenCV, then I would like to put my new Image in the original ImageView.

I tried this way, but :

public class VerifianceActivity extends Activity {
    /** Called when the activity is first created. */   
    private BaseLoaderCallback mLoaderCallback = new BaseLoaderCallback(this) {
        @Override
        public void onManagerConnected(int status) {
            if (status == LoaderCallbackInterface.SUCCESS ) {
                // now we can call opencv code !

                Bitmap mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.cmc7);
                Mat myMat = new Mat();
                Utils.bitmapToMat(mBitmap, myMat);

                Imgproc.cvtColor(myMat, myMat, Imgproc.COLOR_BGR2GRAY);
                Utils.matToBitmap(myMat, mBitmap);

                ImageView mIV = (ImageView) findViewById(R.id.imageView);
                mIV.setImageBitmap(mBitmap);//NPE
                //this line is suppose to work, but the app crashes.
                setContentView(R.layout.main);

            } else {
                super.onManagerConnected(status);
            }
        }
    };

    @Override
    public void onResume() {;
        super.onResume();
        OpenCVLoader.initAsync(OpenCVLoader.OPENCV_VERSION_2_4_5,this, mLoaderCallback);
        // you may be tempted, to do something here, but it's *async*, and may take some time,
        // so any opencv call here will lead to unresolved native errors.
    }
}

Any advice ? I got a NullPointerException as an error

Answer 1

The problem is you need to call

setContentView(R.layout.main);

BEFORE accessing any Views or they will be null such as

 ImageView mIV = (ImageView) findViewById(R.id.imageView);

Since the Views exist inside the layout which you inflate with setContentView() , they don't exist until you inflate that layout so they will return null if you try to initialize them before inflating the Layout

Answer 2

you have to call findViewById after setContentView not before, otherwise the view hierarchy does not exist, and findViewById returns null

  setContentView(R.layout.main);

  ImageView mIV = (ImageView) findViewById(R.id.imageView);
  mIV.setImageBitmap(mBitmap);
  //this line is suppose to work, but the app crashes.

Answer 3

I think you have to do

            setContentView(R.layout.main);

before

            ImageView mIV = (ImageView) findViewById(R.id.imageView);
            mIV.setImageBitmap(mBitmap);

Answer 4

you have to call

setContentView(R.layout.main);

in onCreate(), at least, before trying to call findViewById(..)

i bet, your imageview is null, because it could not find the resource.

ImageView mIV = (ImageView) findViewById(R.id.imageView);