黄沙百战穿金甲
不破楼兰终不还

前言

通过封装PageView+Timer实现无限轮播,手动拖拽时停止定时器功能，拖拽完成后开启定时器。

功能

1. 自动轮播
2. 手动轮播
3. 指示器

功能展示

代码实现

轮播组件的构造方法

  class Carousel extends StatefulWidget {
  final List<BannerModel> banners; // BannerModel是每个item对应的模型 必传参数
  final OnTapBannerItem onTap, // `必传参数` 传入点击每个item的方法
  final Color indicatorNormalColor;// 指示器球的正常颜色
  final Color indicatorCurrentColor;// 指示器球的当前颜色
  final double indicatorWidth;// 指示器球的宽高
  final double indicatorMargin;// 指示器球之间间距
  final bool  hiddenIndicator;// 是否影藏指示器
  final bool  hiddenIndicatorForSingle;// 单个图片是否影藏指示器
  final bool  autoScroll; // 是否循环
  final int  seconds; // 轮播间隔

  Carousel(
      {Key key,
        @required this.banners,
        @required this.onTap,
        this.seconds = 5, // 不传 默认5秒 轮播一次
        this.autoScroll = true,
        this.hiddenIndicator = false,
        this.hiddenIndicatorForSingle = true,
        this.indicatorWidth = 6,
        this.indicatorMargin = 1.5,
        this.indicatorCurrentColor = Colors.white,
        this.indicatorNormalColor = Colors.grey})
      : super(key: key);
  @override
  State<StatefulWidget> createState() {
    return _BannerState();
  }
}

组件状态实现方法

    class _BannerState extends State<Carousel> {

  int _currentIndex = 1;
  PageController controller = PageController(initialPage: 1, viewportFraction: 1);
  Timer _timer;
  
  @override
  void initState() {
    super.initState();
    if(widget.banners.length == 0) return;
    controller = PageController(initialPage: 1);
    if(widget.autoScroll && widget.banners.length > 1) {
      _setTimer();
    }
  }
  // 创建定时器
  _setTimer(){
    _timer = Timer.periodic(Duration(seconds: widget.seconds), (timer) { // 自动滚动
      /// print(realIndex);
      controller.animateToPage(_currentIndex + 1,
          duration: Duration(milliseconds: 300),
          curve: Curves.linear);
    });
  }

  @override
  // 页面退出时销毁定时器
  void dispose() {
    super.dispose();
    controller.dispose();
    _timer.cancel();
  }

  // 是否显示指示器
  _showIndicator() {
    if(widget.banners.length == 0) return false;
    if(widget.hiddenIndicator) return false;
    if(widget.banners.length==1 && widget.hiddenIndicatorForSingle) return false;
    return true;
  }
  // pageView是否可以滚动
  _isCanScroll() {
    if(widget.banners.length == 0 || widget.banners.length == 1) return false;
    return true;
  }

  @override
  Widget build(BuildContext context) {
    List<BannerModel> _list = List();
    if(widget.banners.length > 0) {
      _list
        ..add(widget.banners[widget.banners.length - 1])
        ..addAll(widget.banners)
        ..add(widget.banners[0]);
    }

    return widget.banners.length>0? Container(
      child: Stack(
          alignment: Alignment.bottomCenter,
          children: <Widget>[
            NotificationListener(
              onNotification: (ScrollNotification notification) {
                if(widget.autoScroll && widget.banners.length > 1) {
                  if (notification.depth == 0 &&
                      notification is ScrollStartNotification) {
                    if (notification.dragDetails != null) {
                      _timer.cancel();
                    }
                  } else if (notification is ScrollEndNotification) {
                    _timer.cancel();
                    _setTimer();
                  }
                }
              },
              child:_pageView(_list),
            ),

            _showIndicator() ? _buildIndicator() : Container(), // 下面的小点
          ]),
    ) : Container();
  }
  // 创建轮播View
  Widget _pageView(List _list) {
     return PageView(
      controller: controller,
      onPageChanged: (page) {
        int newIndex;
        if (page == _list.length - 1) {
          newIndex = 1;
          controller.jumpToPage(newIndex);
        } else if (page == 0) {
          newIndex = _list.length - 2;
          controller.jumpToPage(newIndex);
        } else {
          newIndex = page;
        }
        setState(() {
          _currentIndex = newIndex;
        });
      },
      children: _list.map((model) => _buildItem(model)).toList(),
      physics: _isCanScroll() ? AlwaysScrollableScrollPhysics() : NeverScrollableScrollPhysics(),
    );
  }
  // 创建item
  Widget _buildItem(BannerModel model) {
    Image image = Image.asset(model.image, fit: BoxFit.cover);
    if(model.url != null) image = Image.network(model.url, fit: BoxFit.cover);

    return GestureDetector(
      onTap: () { // 按下
        if (widget.onTap != null) {
          widget.onTap(model);
        }
      },
      child: Stack(
        fit: StackFit.expand,
        children: <Widget>[
          image,
        ],
      ),
    );
  }
  // 创建指示器
  Widget _buildIndicator() {
     return Positioned(
      bottom: 15.0,
      left: 0,
      right: 0,
      child: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: widget.banners
            .asMap()
            .map((i, v) => MapEntry(
            i,
            Container(
              width: widget.indicatorWidth,
              height: widget.indicatorWidth,
              margin: EdgeInsets.only(left: 2.0, right: 2.0),
              decoration: ShapeDecoration(
                  color: _currentIndex == i + 1
                      ? widget.indicatorCurrentColor
                      : widget.indicatorNormalColor,
                  shape: CircleBorder()),
            )))
            .values
            .toList(),
      ),
    );
  }
}
typedef void OnTapBannerItem(BannerModel model);

模型实现

根据自己的需要实现对应的模型

    class BannerModel extends Object {
      final String image;// 本地图片路径
      final String url; // 网络URL
        
      // 当有网络连接时会优先使用网络图片，没有则使用本地图片
      BannerModel(this.url, {this.image});// image为可选参数，
    }

源码地址

链接描述