月度归档： 2020年6月

实现一个轮播

在PC端实现轮播一般都是直接使用JavaScript库进行实现.但在Flutter上想要实现一个轮播,可能只有自己写一下了.

轮播的特点:

1. 可以自动播放;
2. 图片可以左右滑动(使用Flutter自带的PageView初始只能向右滑动,不能向左);
3. 可以定义自动播放的间隔时间.

大概就这么几个特点,可以实现个简单的例子.

功能部分

目前仅实现简单功能:
1. 可以自定义网络图片或本地图片(可以混用本地图片和网络图片),
2. 自定义图片切换时间,
3. 自定义是否开启自动轮播.

上述几条可以满足一个简单轮播的需要,如果需要更多功能.可以在此基础上增加.

源码

完整代码: Gitee仓库

/// 轮播组件
///
///  目前仅实现简单功能:
///   1. 可以自定义网络图片或本地图片(可以混用本地图片和网络图片),
///   2. 自定义图片切换时间,
///   3. 自定义是否开启自动轮播.
///
///  调用示例:
///
///  ```dart
///  static const List _images = [
///   'assets/images/3302e58f9a181d2509f3dc0fa68b0jpeg.jpeg',
///   'assets/images/19aa98b1fcb2781c4fba33d850549jpeg.jpeg',
///   'https://fuss10.elemecdn.com/0/6f/e35ff375812e6b0020b6b4e8f9583jpeg.jpeg',
///   'https://fuss10.elemecdn.com/9/bb/e27858e973f5d7d3904835f46abbdjpeg.jpeg',
///   'https://fuss10.elemecdn.com/d/e6/c4d93a3805b3ce3f323f7974e6f78jpeg.jpeg',
///   'https://fuss10.elemecdn.com/3/28/bbf893f792f03a54408b3b7a7ebf0jpeg.jpeg',
///   'https://fuss10.elemecdn.com/2/11/6535bcfb26e4c79b48ddde44f4b6fjpeg.jpeg',
///   'https://fuss10.elemecdn.com/a/3f/3302e58f9a181d2509f3dc0fa68b0jpeg.jpeg',
///   'https://fuss10.elemecdn.com/1/34/19aa98b1fcb2781c4fba33d850549jpeg.jpeg',
///   'https://fuss10.elemecdn.com/0/6f/e35ff375812e6b0020b6b4e8f9583jpeg.jpeg'
///  ];
///
/// ......
///
/// SizedBox(
//            width: double.infinity,
//            height: 200,
//            child: Carousel(
//              _images,
//              autoPlayer: false,
//            ),
//          ),
///
/// ```
///
///
///
///
class Carousel extends StatefulWidget {
  Carousel(
    this.imagesList, {
    Key key,
    this.autoPlayer = true,
    this.seconds = 5,
  })  : assert(imagesList.isNotEmpty),
        assert(seconds > 2),
        super(key: key);

  final int _maxPage = 2000000000;

  /// 轮播切换间隔秒数.
  final int seconds;

  /// 是否自动播放
  final bool autoPlayer;

  final List imagesList;

  @override
  _CarouselState createState() => new _CarouselState();
}

class _CarouselState extends State {

  PageController _pageController;
  Timer _timer;

  var _currIndex = 0;

  @override
  void initState() {
    super.initState();
    if (widget.autoPlayer) {
      startTimeout();
    }
    _pageController = new PageController(initialPage: widget._maxPage);
  }

  @override
  void dispose() {
    super.dispose();
    _pageController.dispose();
    if (_timer != null) {
      _timer.cancel();
    }

  }

  void startTimeout() {
    var timeout = Duration(seconds: widget.seconds);
    Timer.periodic(timeout, (Timer timer) {
      var tempIndex = _currIndex + 1;
      if (tempIndex >= widget.imagesList.length) {
        tempIndex = 0;
      }
      setState(() {
        _timer = timer;
        _currIndex = tempIndex;
      });
    });
  }

  List getBottomIcon() {
    var forLength = widget.imagesList.length;
    var res = List();
    for (var i = 0; i < forLength; i++) {
      if (_currIndex == i) {
        res.add(GestureDetector(
          /// 选中时的图标,可以更换为图片.
          child: Icon(Icons.brightness_1),
          onTap: () {
            setState(() {
              _currIndex = i;
            });
          },
        ));
      } else {
        res.add(GestureDetector(
          /// 未选中时的图标,可以更换为图片.
          child: Icon(Icons.panorama_fish_eye),
          onTap: () {
            setState(() {
              _currIndex = i;
            });
          },
        ));
      }
    }
    return res;
  }

  @override
  Widget build(BuildContext context) {
    var width = MediaQuery.of(context).size.width;
    return Scaffold(
      body: PageView.builder(
          controller: _pageController,
          onPageChanged: (int index) {
            var renderIndex = index - widget._maxPage;
            renderIndex = renderIndex % widget.imagesList.length;
            if (renderIndex < 0) {
              renderIndex += widget.imagesList.length;
            }
            setState(() {
              _currIndex = renderIndex;
            });
          },
          itemBuilder: (BuildContext context, int index) {
            var renderIndex = _currIndex - widget._maxPage;
            renderIndex = renderIndex % widget.imagesList.length;
            if (renderIndex < 0) {
              renderIndex += widget.imagesList.length;
            }
            return Container(
                child: Stack(children: [
              Center(
                child: widget.imagesList[_currIndex].startsWith("https://") ||
                        widget.imagesList[_currIndex].startsWith("http://")
                    ? CachedNetworkImage(
                        imageUrl: widget.imagesList[_currIndex],
                        fit: BoxFit.fill,
                        width: width,
                        height: double.infinity,
                        placeholder: (context, url) =>
                            CircularProgressIndicator(),
                        errorWidget: (context, url, error) => Icon(Icons.error),
                      )
                    : FadeInImage(
                        image: AssetImage(widget.imagesList[_currIndex]),
                        placeholder: AssetImage("assets/images/loading.gif"),
                        fit: BoxFit.fill,
                        width: width,
                        height: double.infinity,
                      ),
              ),
              Positioned(
                  left: 2.0,
                  right: 2.0,
                  bottom: 10.0,
                  child: Container(

                      /// padding: EdgeInsets.all(5.0),
                      child: widget.imagesList.length > 10
                          ? SingleChildScrollView(
                              scrollDirection: Axis.horizontal,
                              child: Row(
                                mainAxisAlignment: MainAxisAlignment.center,
                                crossAxisAlignment: CrossAxisAlignment.start,
                                children: getBottomIcon(),
                              ),
                            )
                          : Row(
                              mainAxisAlignment: MainAxisAlignment.center,
                              crossAxisAlignment: CrossAxisAlignment.start,
                              children: getBottomIcon(),
                            )))
            ]));
          }),
    );
  }
}