title: How to make a set of ObjectAnimator loop?
body: <p>I want to make a Animation like heartbeat, one picture quickly change its ALPHA from 0 to 1 ,and slowly from 1 to 0. I define that in XML file.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;set xmlns:android="http://schemas.android.com/apk/res/android"
      android:ordering="sequentially"&gt;
      &lt;objectAnimator
          android:propertyName="alpha"
          android:valueFrom="0"
          android:valueTo="1"
          android:valueType="floatType"
          android:duration="700"/&gt;
      &lt;objectAnimator
          android:propertyName="alpha"
          android:valueFrom="1"
          android:valueTo="0"
          android:valueType="floatType"
          android:duration="1500"/&gt;
  &lt;/set&gt;
  </code></pre>
  
  <p>and I use them in Java Code.</p>
  
  <pre><code>private void cursorHeartBeatAnimation() {
      Animator animator = AnimatorInflater.loadAnimator(this, R.animator.cursor_heartbeat);
      animator.setTarget(this.cursor);
      animator.setStartDelay(1500);
      animator.start();
  }
  </code></pre>
  
  <p>and I want to let them play all the time, How to do it?</p>