ObjectAnimator fade in and out

TextView t;
    Animation a;
    //ObjectAnimator anim;
    AnimatorSet set = new AnimatorSet();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        t = (TextView) findViewById(R.id.text);
        a = AnimationUtils.loadAnimation(this, R.anim.fade_in);

        /*t.post(new Runnable() {

            @Override
            public void run() {
                // TODO Auto-generated method stub
                t.startAnimation(a);
            }
        });*/
        Button b = (Button) findViewById(R.id.btn);
        b.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                //t.startAnimation(a);
                //anim.start();
                set.start();
            }
        });

        ObjectAnimator fadeOut = ObjectAnimator.ofFloat(t, "alpha", 1f, 0f);
        ObjectAnimator fadeIn = ObjectAnimator.ofFloat(t, "alpha", 0f, 1f);
        fadeOut.setDuration(2000);
        fadeIn.setDuration(2000);
        set.playSequentially(fadeIn , fadeOut);
    }