I can't play an animation with a Timer

Question

When I try to animate an image from a Timer I can't do it, however the Toast is executed. The animation works correctly because I tested from a button.It is rare, only the Toast runs and does not fail the application. Someone could help me!

public class Ayuda extends Activity {
        ImageView imagen_toro, imagen_vaca;
        Animation rotar;
        Timer timer;
        TimerTask timerTask;
        final Handler handler = new Handler();

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_ayuda);

            imagen_toro = (ImageView) findViewById(R.id.imagen_toro_ayuda);
            imagen_vaca = (ImageView) findViewById(R.id.imagen_vaca_ayuda);
            rotar = AnimationUtils.loadAnimation(this, R.animator.animar_toro);

            timer = new Timer();
            timerTask = new TimerTask() {
                public void run() {
                    runOnUiThread(new Runnable() {
                        public void run() {
                            rotar.reset();
                            imagen_toro.setAnimation(rotar);
                            rotar.reset();
                            imagen_vaca.setAnimation(rotar);
                            int duration = Toast.LENGTH_SHORT;  
                            Toast toast = Toast.makeText(getApplicationContext(), "test", duration);
                            toast.show();
                        }
                    });
                }
            };
            timer.schedule(timerTask, 3000, 3000); //
        }   
    }

Answer 1

As a first, you should use PostDealyed instead of timer. also, you need to call start animation

        imageView.postDelayed(new Runnable() {

            @Override
            public void run() {
                imagen_toro.startAnimation(animation) 

            }
        }, 3000);

Answer 2

In general, using Timer is considered bad practice. Even Android documentation advises to use ScheduledThreadPoolExecutor in general case of running recurring tasks. Moreover, Android animations should be run using animation-specific APIs to avoid mistakes.

I suggest using rotar.setAnimationListener() to restart animation with imagen_vaca.startAnimation(rotar);

Also you should consider using new Animators API.