Flutter中实现一个无限轮询的Banner

在flutter中写banner图的时候，用了第三方库banner时发现有些小问题，所以自己来实现以下。 通过学习和测试，然后直接上代码吧。 原理都和Android中是一样的，只不过是做个记录罢了，方便以后自己使用，顺便给需要的人提供个方便。

import 'dart:async';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

void main() => runApp(BannerTest());

class BannerTest extends StatefulWidget {
  @override
  _BannerTestState createState() => _BannerTestState();
}

class _BannerTestState extends State {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
        title: Text("Banner"),
        ),
        body: ListView.builder(
            itemCount: 10,
            itemBuilder: (context, i) {
              if (i == 0) {
                return Container(
                    height: 180,
                    child: BannerView(
                      children: [
                        Image.network(
                            "https://www.wanandroid.com/blogimgs/50c115c2-cf6c-4802-aa7b-a4334de444cd.png",
                            fit: BoxFit.cover),
                        Image.network(
                            "https://www.wanandroid.com/blogimgs/90c6cc12-742e-4c9f-b318-b912f163b8d0.png",
                            fit: BoxFit.cover),
                        Image.network(
                            "https://www.wanandroid.com/blogimgs/ab17e8f9-6b79-450b-8079-0f2287eb6f0f.png",
                            fit: BoxFit.cover),
                        Image.network(
                            "https://www.wanandroid.com/blogimgs/fb0ea461-e00a-482b-814f-4faca5761427.png",
                            fit: BoxFit.cover),
                        Image.network(
                            "https://www.wanandroid.com/blogimgs/62c1bd68-b5f3-4a3c-a649-7ca8c7dfabe6.png",
                            fit: BoxFit.cover),
                        Image.network(
                            "https://www.wanandroid.com/blogimgs/00f83f1d-3c50-439f-b705-54a49fc3d90d.jpg",
                            fit: BoxFit.cover),
                      ],
                    ));
              } else {
                return Text("");
              }
            }),
      ),
    );
      }
    }

class BannerView extends StatefulWidget {
  final List children;

  final Duration switchDuration;

  BannerView(
      {this.children = const [],
      this.switchDuration = const Duration(seconds: 3)});

  @override
  _BannerViewState createState() => _BannerViewState();
}

class _BannerViewState extends State
    with SingleTickerProviderStateMixin {
  TabController _tabController;
  PageController _pageController;
  Timer _timer;
  int _curPageIndex;
  static const Duration animateDuration = const Duration(milliseconds: 500);

  List children = [];

  @override
  void initState() {
    super.initState();
    _curPageIndex = 0;

    _tabController = TabController(length: widget.children.length, vsync: this);
    /// 添加所有的widget到新建的list中
    children.addAll(widget.children);
    /// 定时器完成自动翻页-只有在大于1时才会有翻页
    if (children.length > 1) {
      children.insert(0, widget.children.last);
      children.add(widget.children.first);
      ///如果大于一页，则会在前后都加一页， 初始页要是 1
      _curPageIndex = 1;
      _timer = Timer.periodic(widget.switchDuration, _nextBanner);
    }

    ///初始页面 指定
    _pageController = PageController(initialPage: _curPageIndex);
  }
  /// 进行翻页的动画
  _nextBanner(Timer timer) {
    _curPageIndex++;
    _curPageIndex = _curPageIndex == children.length ? 0 : _curPageIndex;

    //curve:和android一样 动画插值
    _pageController.animateToPage(_curPageIndex,
        duration: animateDuration, curve: Curves.linear);
  }


  @override
  void dispose() {
    /// 页面销毁时进行回收
    _pageController.dispose();
    _tabController.dispose();
    _timer?.cancel();
    super.dispose();
}
  @override
  Widget build(BuildContext context) {
    return Stack(
      children: [
        Listener(
          /// 点击时取消timer效果
          onPointerDown: (_) => _timer?.cancel(),
          onPointerUp: (_) {
            ///重新开启timer
            if (children.length > 1) {
              _timer = Timer.periodic(widget.switchDuration, _nextBanner);
            }
          },
          child: NotificationListener(
            onNotification: (notification){
              if(notification is ScrollUpdateNotification) {
                ScrollUpdateNotification n = notification;
                /// 判断是否是一次完整的翻页
                if (n.metrics.atEdge) {
                  if (_curPageIndex == children.length - 1) {
                    /// 如果是最后一页，那么就跳到第一页
                    _pageController.jumpToPage(1);
                  } else if (_curPageIndex == 0) {
                    /// 如果是第一页，再往前滑动，因为原来的list前后都加了一条数据，所以 -2
                    _pageController.jumpToPage(children.length - 2);
                  }
                }
              }
            },
            child: PageView.builder(
              itemCount: children.length,
              itemBuilder: (context, index) {
                 /// banner设置点击监听
                return InkWell(
                  child: children[index],
                  onTap: () {
                    print("点击Item");
                  },
                );
              },
              onPageChanged: (index) {
                _curPageIndex = index;
                if (index == children.length - 1) {
                  /// 如果是最后一页，那么下面的指示器设置为0的位置
                  _tabController.animateTo(0);
                } else if(index == 0){
                  ///如果是第一页再往左滑，那么久设置为指示器最后的位置
                  _tabController.animateTo(_tabController.length-1);
                }else {
                  _tabController.animateTo(index-1);
                }
              },
              controller: _pageController,
            ),
          )
        ),
        Positioned(
          child: TabPageSelector(
           controller: _tabController,
            color: Colors.white,
            selectedColor: Colors.grey,
          ),
          bottom: 8.0,
          right: 8.0,
        ),
      ],
    );
  }
}

可以直接跑起来的，就不做过多讲解了。