<in.srain.cube.views.ptr.PtrFrameLayout xmlns:android="http://schemas.android.com/apk/res/android" 
  android:id="@+id/ptr_layout_activity" 
  android:layout_width="match_parent" 
  android:layout_height="match_parent" 
  android:clipChildren="false"> 

@Override 
  public void onUIPositionChange(PtrFrameLayout frame, boolean isUnderTouch, byte status, PtrIndicator ptrIndicator) { 
    //下拉距离 
    posY = ptrIndicator.getCurrentPosY(); 
    if (!isRefresh) { 
      if (isComplete) { 
        //刚刚完成了下拉刷新操作,还没有重置事件。使用图片2.保持上下边距，下拉上推底部弧线不显示 
        drawable = ResourcesUtils.getDrawable(R.drawable.home_loading_1); 
        flag = 4; 
      } else { 
        //未触发下拉刷新时拉着玩 
        if (posY < turning) { 
          //使用图片1 
          drawable = ResourcesUtils.getDrawable(R.drawable.home_loading_0); 
          flag = 0; 
        } else if (posY < measureHeight * RATIO_TO_REFRESH) { 
          //使用图片1 
          //显示下面的弧线 
          drawable = ResourcesUtils.getDrawable(R.drawable.home_loading_0); 
          flag = 1; 
        } else { 
          //下拉距离已经达到了可以触发下拉刷新的位置。使用图片2 
          drawable = ResourcesUtils.getDrawable(R.drawable.home_loading_1); 
          flag = 2; 
        } 
      } 
    } else { 
      //当前正在下拉刷新的时候.自己手动去滑动图片不做变化 
      flag = 3; 
      if (!animation.isHasStart()) { 
        startAnimation(animation); 
        animation.setHasStart(true); 
      } 
    } 
    invalidate(); 
  } 

Drawable animationDrawable = ResourcesUtils.getDrawable(R.drawable.home_loading_2); 
measureHeight = padding * 2 + animationDrawable.getIntrinsicHeight(); 

switch (flag) { 
      case 1: 
      case 2: 
        controlY = (int) ((posY - turning) * RATIO_TO_REFRESH) > dragDistance * 2 
            ? dragDistance * 2 + measureHeight : (int) ((posY - turning) * RATIO_TO_REFRESH) 
            + measureHeight; 
        //下拉弧度 
        mPath.reset(); 
        mPath.moveTo(0, measureHeight); 
        mPath.quadTo(getWidth() / 2, controlY, getWidth(), measureHeight); 
        mPath.lineTo(getWidth(), 0); 
        mPath.lineTo(0, 0); 
        mPath.close(); 
 
        mDrawableRect.set((getWidth() - drawable.getIntrinsicWidth()) / 2, 
            getBsrPositionY(controlY) - drawable.getIntrinsicHeight() * 2 / 3, 
            (canvas.getWidth() + drawable.getIntrinsicWidth()) / 2, 
            getBsrPositionY(controlY) + drawable.getIntrinsicHeight() / 3); 
 
        //绘制弧线 
        mPaint.setXfermode(null); 
        canvas.drawPath(mPath, mPaint); 
        canvas.save(); 
        canvas.clipPath(mPath); 
        drawable.setBounds(mDrawableRect); 
        drawable.draw(canvas); 
        canvas.restore(); 
        break; 

/** 
   * 获取贝塞尔曲线最高点位置 
   * 
   * @param y 中间控制点的y坐标 
   * @return 
   */ 
  private int getBsrPositionY(int y) { 
    //起点和终点确定的 
    return measureHeight + (y - measureHeight) / 2; 
  } 

mDrawableRect.set((getWidth() - drawable.getIntrinsicWidth()) / 2, 
              padding, 
              (getWidth() + drawable.getIntrinsicWidth()) / 2, 
              padding + drawable.getIntrinsicHeight()); 
          if (drawable != null) { 
            drawable.setBounds(mDrawableRect); 
            drawable.draw(canvas); 
          } 
          if (SystemClock.elapsedRealtime() - lastTime > DURATION) { 
            //超过间隔后刷新动画 
            changeDrawable(); 
            lastTime = SystemClock.elapsedRealtime(); 
          } 

class MyAnimation extends Animation { 
 
    boolean hasStart; 
 
    public boolean isHasStart() { 
      return hasStart; 
    } 
 
    public void setHasStart(boolean hasStart) { 
      this.hasStart = hasStart; 
    } 
 
    @Override 
    public void initialize(int width, int height, int parentWidth, int parentHeight) { 
      super.initialize(width, height, parentWidth, parentHeight); 
      setDuration(mDurationToClose); 
      //设置动画结束后保留效果 
 
      setInterpolator(new AccelerateDecelerateInterpolator()); 
    } 
 
    @Override 
    protected void applyTransformation(float interpolatedTime, Transformation t) { 
      super.applyTransformation(interpolatedTime, t); 
      //从0-1.逐渐变化(弧线回弹动画)，位置从controlY到0变化 
      flag = 3; 
      proportion = interpolatedTime; 
      invalidate(); 
    } 
  } 

case 3: 
        //正在刷新时，执行弹上去的动画 
        if (proportion < 1.0f) { 
          mPath.reset(); 
          mPath.moveTo(0, measureHeight); 
          mPath.quadTo(getWidth() / 2, (controlY - measureHeight) * (1 - proportion) + measureHeight, getWidth(), measureHeight); 
          mPath.lineTo(getWidth(), 0); 
          mPath.lineTo(0, 0); 
          mPath.close(); 
          canvas.drawPath(mPath, mPaint); 
          mDrawableRect.set((getWidth() - drawable.getIntrinsicWidth()) / 2, 
              (int) ((getBsrPositionY((int) controlY) - drawable.getIntrinsicHeight() - padding) * (1 - proportion)) + padding, 
              (getWidth() + drawable.getIntrinsicWidth()) / 2, 
              (int) ((getBsrPositionY((int) controlY) - (padding + drawable.getIntrinsicHeight())) * (1 - proportion)) + (padding + drawable.getIntrinsicHeight())); 
          if (drawable != null) { 
            drawable.setBounds(mDrawableRect); 
            drawable.draw(canvas); 
          } 
        } else {..} 

case 4: 
        //刷新完成后,图片此时换成了1，变小了。也要保持图片的居中 
        mDrawableRect.set((getWidth() - drawable.getIntrinsicWidth()) / 2, 
            (measureHeight - drawable.getIntrinsicHeight()) / 2, 
            (getWidth() + drawable.getIntrinsicWidth()) / 2, 
            (measureHeight + drawable.getIntrinsicHeight()) / 2); 
        if (drawable != null) { 
          drawable.setBounds(mDrawableRect); 
          drawable.draw(canvas); 
        } 
        break; 

case 0: 
    default: 
        //图片位置 
        mDrawableRect.set((getWidth() - drawable.getIntrinsicWidth()) / 2, 
            measureHeight - drawable.getIntrinsicHeight(), 
            (getWidth() + drawable.getIntrinsicWidth()) / 2, 
            measureHeight); 
        if (drawable != null) { 
          drawable.setBounds(mDrawableRect); 
          drawable.draw(canvas); 
        } 
        break;