flutter简单自定义跟随手指滑动的横向指示器

ScrollController _scrollController = ScrollController();

  double _scrollIndicatorWidth = 60.w;//指示器的长度
  double _maxScrollPaddingValue = 30.w;//指示器中蓝条可移动的最大距离
  double _scrollPaddingValue = 0.0;//指示器中蓝条左边距(蓝条移动距离)

@override
  void initState() {
    super.initState();
    _scrollController.addListener(() {
      setState(() {
        final double scrollOffset = _scrollController.offset;
        final double? scrollableExtent = _scrollController.position.maxScrollExtent;
      //  final double viewportExtent = _scrollController?.position?.viewportDimension;
        if(scrollableExtent != null){
          _scrollPaddingValue = (scrollOffset / scrollableExtent) * _maxScrollPaddingValue;
        }
        if(_scrollPaddingValue > _maxScrollPaddingValue){
          _scrollPaddingValue = _maxScrollPaddingValue;
        }
      });
    });
  }
@override
  void dispose() {
    _scrollController.dispose();
    super.dispose();
  }

//横向tab布局
_goodsTabBar() {
    if(_goodsCategoryList.isNotEmpty){
      return Column(
        children: [
          SingleChildScrollView(
              controller: _scrollController,
              scrollDirection: Axis.horizontal,
              child:TabBar(
                controller: _tabController,
                // tabs的长度超出屏幕宽度后，TabBar，是否可滚动
                isScrollable: true,
                // 设置tab文字的类型
                labelStyle: TextStyle(
                    fontSize: 24.sp, letterSpacing: 1),
                // 设置tab选中得颜色
                labelColor: JadeColors.green_7,
                labelPadding: EdgeInsets.symmetric(horizontal: 10.w),
                // 设置tab未选中的颜色
                unselectedLabelColor: JadeColors.grey,
                // 设置tab未选中时文字的类型
                unselectedLabelStyle: TextStyle(fontSize: 24.sp, letterSpacing: 1),
                indicatorWeight: 0.01,
                indicatorColor: JadeColors.grey_2,
                tabs: _goodsCategoryList.asMap().entries
                    .map((entry){
                  int index = entry.key;
                  GoodsCategoryBean value = entry.value;
                  bool isSelect = _tabController!.index == index;
                  return Column(
                    children: [
                      Container(
                        margin: EdgeInsets.only(top: 40.w,bottom: 10.w),
                        width: 90.w,height: 90.w,
                        decoration: BoxDecoration(
                          border: isSelect
                              ? Border.all(color: JadeColors.green_7, width: 0.8)
                              : null,
                          borderRadius: BorderRadius.circular(5),
                        ),
                        child: Image.asset(value.iconPath ?? PathConfig.aTuiLogo),
                      ),
                      Text(value.name!)
                    ],
                  );
                }).toList(),
              )
          ),
          _scrollIndicator()
        ],
      );
    }else{
      return SizedBox.shrink();
    }
  }