Switching images with a delay

Question

I want my app to switch two images with a delay of, let's say, 3 seconds. This is my former code:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    if (savedInstanceState == null) {
        getFragmentManager().beginTransaction()
                .add(R.id.container, new PlaceholderFragment())
                .commit();
    }

    Handler handler = new Handler();
    handler.postDelayed(new Runnable() {

        @Override
        public void run() {
            ImageView image = (ImageView)      
 findViewById(R.id.imgView_dice0);
            image.setImageResource(R.drawable.dice_6);      
        }
    }, 3000);
}
....

This works for switching the image one time. I tried putting the image-changing in two methods (and replacing R.drawable.dice_6 with R.drawable.dice_1) which are called with a delay, surrounded by a loop. That doesn't work, the app only shows one and the same dice all the time. What should I do?

Answer 1

You should restart your Handler.postDelayed inside the runnable to make it work.

Something like:

final Handler handler = new Handler();
handler.postDelayed(new Runnable() {
    private boolean useDiceOne;

    @Override
    public void run() {
        ImageView image = (ImageView)findViewById(R.id.imgView_dice0);
        if (!useDiceOne) {
         image.setImageResource(R.drawable.dice_6);
        } else {
         image.setImageResource(R.drawable.dice_1);
        }
        useDiceOne = !useDiceOne;
        handler.postDelayed(this, 3000);      
    }
 }, 3000);

useDiceOne will be used to change the image between dice_1 and dice_6 p.s cache the ImageView.

To make it more flexible (stop it when you want, etc.) you could save the handler reference (and runnable reference too) somewhere and use removeCallbacks