//定義兩個變量，這個兩個變量是表示滑動時候，positionOffset 是從大到
 //小的變化，還是從小到大的變化。用于在滑動時候，避免多次調用一個方法
 private boolean isSmallToBig = true;
 private boolean isBigToSmall = false;

  //記錄上一次滑動的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) {
    
    //設定滑動的邊界，這里設置的滑動到一半
    float radiusOffsetHead = 0.5f;
    //如果滑動小于一半，通過isSmallToBig這個變量來避免多次調用
    // initIndicatorView 方法
    if (positionOffset <= radiusOffsetHead && !isSmallToBig) {

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

    } else if (positionOffset > radiusOffsetHead && !isBigToSmall) {
     //超過一半。如果是左滑，就-1，如果是右滑，就+1
      int currnt = isLeft &#63; mCurrentPage + 1 : mCurrentPage - 1;
      initIndicatorView(currnt);
      isBigToSmall = true;
      isSmallToBig = false;
    }
  }