How to use

setOnPageChangeListener

method

in

androidx.viewpager.widget.ViewPager

private void initViewPager(AttributeSet attrs, int defStyleAttr) {
  super.setOnPageChangeListener(internalOnPageChangeListener);
  final ViewConfiguration configuration = ViewConfiguration.get(getContext());
  mTouchSlop = configuration.getScaledTouchSlop();
  TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.ViewPager, defStyleAttr, R.style.carbon_ViewPager);
  for (int i = 0; i < a.getIndexCount(); i++) {
    int attr = a.getIndex(i);
    if (attr == R.styleable.ViewPager_carbon_overScroll) {
      setOverScrollMode(a.getInt(attr, OVER_SCROLL_ALWAYS));
    }
  }
  Carbon.initTint(this, a, tintIds);
  a.recycle();
  setWillNotDraw(false);
}

public static  ViewPagerHelper addSelectPos(final ViewPager vp, final SelectPosCallback callback) {
  final ViewPagerHelper vpHelper = new ViewPagerHelper();
  vp.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
    @Override
    public void onPageScrolled(final int position, float positionOffset, int positionOffsetPixels) {
      if (vpHelper.state == -1&&callback!=null)
        callback.selected(vp.getCurrentItem());
      vpHelper.log("onPageScrolled:" + position +
          "\t positionOffset:" + positionOffset + "\t positionOffsetPixels:" + positionOffsetPixels);
    }
    @Override
    public void onPageSelected(int position) {
      vpHelper.log("onPageSelected:" + position);
      callback.selected(position);
    }
    @Override
    public void onPageScrollStateChanged(int state) {
      vpHelper.log("state:" + state);
      vpHelper.state = state;
    }
  });
  return vpHelper;
}

viewpagerItem.setOverScrollMode(View.OVER_SCROLL_NEVER);
viewpagerItem.setOffscreenPageLimit(1);//预加载数据页
viewpagerItem.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
  @Override
  public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {