android app crashes while timer loop

Question

I'm new here and noob as well. I started learning Java and Android by making my first simple app.

I want to do the time loop to do some function every 1 sec.
I have this:

new Timer().scheduleAtFixedRate(new TimerTask(){
    @Override
    public void run(){
        imV.setImageResource(stageArray.getResourceId(step, -1));
        Log.d("MyApp","I am here");
        step ++;
    }
},0,1000);

It's in my init() function.
After I run this on my device, the app crashes.
When I delete the imV.setImageRes... line it runs, but I don't get log notifications.
The step value is changing.
Something similiar is happening when I use a Handler.

So why my app crash?
Why cannot I see any log.d from this loop?
Are there better ways to do time loop to make simple changes?

Answer 1

Your app has crashed because you access the Android UI toolkit from outside the UI thread when you call imV.setImageResource(stageArray.getResourceId(step, -1)); . So that, exception has occurred. You must set image for imageview in UI thread:

runOnUiThread(new Runnable() {
                @Override
                public void run() {
                    imV.setImageResource(stageArray.getResourceId(step, -1));
                }
            });

Or simple solution with CountDownTimer

new CountDownTimer(totalStep * 1000, 1000) {
        @Override
        public void onTick(long millisUntilFinished) {
            step = millisUntilFinished/1000;
            imV.setImageResource(_yourResID);
        }

        @Override
        public void onFinish() {
            Log.d("Finish", "Done");
        }
    }.start();