public void onClick(View v) {
    new Thread(new Runnable() {
        public void run() {
            // a potentially  time consuming task
            final Bitmap bitmap =
                    processBitMap("image.png");
            mImageView.post(new Runnable() {
                public void run() {
                    mImageView.setImageBitmap(bitmap);
                }
            });
        }
    }).start();
}