Question

/**
  * 改变刷新动画的的圆圈刷新状态。Notify the widget that refresh state has changed. Do not call this when
  * refresh is triggered by a swipe gesture.
  *
  * @param refreshing 是否显示刷新的圆圈
  */
 public void setRefreshing(boolean refreshing) {
   if (refreshing && mRefreshing != refreshing) {
     // scale and show
     mRefreshing = refreshing;
     int endTarget = 0;
     if (!mUsingCustomStart) {
       endTarget = (int) (mSpinnerFinalOffset + mOriginalOffsetTop);
     } else {
       endTarget = (int) mSpinnerFinalOffset;
     }
     setTargetOffsetTopAndBottom(endTarget - mCurrentTargetOffsetTop,
         true /* requires update */);
     mNotify = false;
     startScaleUpAnimation(mRefreshListener);
   } else {
     setRefreshing(refreshing, false /* notify */);
   }
 }

startScaleUpAnimation 开启一个动画，然后在动画结束后回调 onRefresh 方法。

private Animation.AnimationListener mRefreshListener = new Animation.AnimationListener() {
   // .. 省略代码
   @Override
   public void onAnimationEnd(Animation animation) {
     if (mRefreshing) {
       mProgress.setAlpha(MAX_ALPHA); //确保刷新圆圈中间的进度条是完全不透明了
       mProgress.start();
       if (mNotify) { // 当 mNotify 为 true 时才会回调 onRefresh
         if (mListener != null) {
           // 回调 listener 的 onRefresh 方法
           mListener.onRefresh();
         }
       }
       mCurrentTargetOffsetTop = mCircleView.getTop();
     } else {
       reset();
     }
   }
};