Android ImageView连续放大和缩小

有什么办法可以放大和缩小ImageView在Android中不断。我尝试使用下面的代码，但只有一个缩放功能可以工作。

缩放.xml

    <?xml version="1.0" encoding="utf-8"?>
    <set xmlns:android="http://schemas.android.com/apk/res/android"
    android:fillAfter="true" > 
    <scale
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:duration="20000"
        android:fromXScale="1"
        android:fromYScale="1"
        android:pivotX="50%"
        android:pivotY="50%"
        android:toXScale="3"
        android:toYScale="3" >
    </scale>

</set>

缩小.xml

    <?xml version="1.0" encoding="utf-8"?>
    <set xmlns:android="http://schemas.android.com/apk/res/android"
    android:fillAfter="true" > 
    <scale
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:duration="20000"
        android:fromXScale="1.0"
        android:fromYScale="1.0"
        android:pivotX="50%"
        android:pivotY="50%"
        android:toXScale="0.5"
        android:toYScale="0.5" >
    </scale>

</set>

And the Activity我的课程：

Animation zoomin, zoomout; //declared as public

@Override
public void onCreate(Bundle savedInstanceState) {
   // animation
    zoomin = AnimationUtils.loadAnimation(this, R.anim.zoomin);
    zoomout = AnimationUtils.loadAnimation(this, R.anim.zoomout);
    bgImage.setAnimation(zoomin);
    bgImage.setAnimation(zoomout);
    Thread t = new Thread(new Zoom());
    t.start();
}
private class Zoom implements Runnable {
    @Override
    public void run() {
        while (true) {              
            bgImage.startAnimation(zoomin);
            try {
                Thread.sleep(8000);
            } catch (InterruptedException e) {
                                    e.printStackTrace();
            }               
            bgImage.startAnimation(zoomout);
        }
    }
}

这里的zoomin动画似乎运行良好。有什么办法可以实现zoomin and zoomout动画连续？？？

Thanks

使用它代替线程

 zoomin.setAnimationListener(new AnimationListener() {

        @Override
        public void onAnimationStart(Animation arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onAnimationRepeat(Animation arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onAnimationEnd(Animation arg0) {
            bgImage.startAnimation(zoomout); 

        }
    });

and

 zoomout.setAnimationListener(new AnimationListener() {

        @Override
        public void onAnimationStart(Animation arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onAnimationRepeat(Animation arg0) {
            // TODO Auto-generated method stub

        }

        @Override
        public void onAnimationEnd(Animation arg0) {
            bgImage.startAnimation(zoomin); 

        }
    });