//定义两个变量，这个两个变量是表示滑动时候，positionOffset 是从大到
 //小的变化，还是从小到大的变化。用于在滑动时候，避免多次调用一个方法
 private boolean isSmallToBig = true;
 private boolean isBigToSmall = false;

  //记录上一次滑动的positionOffsetPixels值
  private int lastValue = -1;
  @Override
  public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    if (positionOffset != 0) {
      mCurrentPage = position;
      boolean isLeft = true;
      if (lastValue >= positionOffsetPixels) {
        //右滑
        isLeft = false;
      } else if (lastValue < positionOffsetPixels) {
        //左滑
        isLeft = true;
      }
      setIndiactorView(positionOffset,isLeft);
    }
    lastValue = positionOffsetPixels;

  }

  private void setIndiactorView(float positionOffset,boolean isLeft) {
    
    //设定滑动的边界，这里设置的滑动到一半
    float radiusOffsetHead = 0.5f;
    //如果滑动小于一半，通过isSmallToBig这个变量来避免多次调用
    // initIndicatorView 方法
    if (positionOffset <= radiusOffsetHead && !isSmallToBig) {

      initIndicatorView(mCurrentPage);
      isSmallToBig = true;
      isBigToSmall = false;

    } else if (positionOffset > radiusOffsetHead && !isBigToSmall) {
     //超过一半。如果是左滑，就-1，如果是右滑，就+1
      int currnt = isLeft ? mCurrentPage + 1 : mCurrentPage - 1;
      initIndicatorView(currnt);
      isBigToSmall = true;
      isSmallToBig = false;
    }
  }