列表滚动监听、移除ListView的padding、透明导航栏

import 'package:flutter/material.dart';
import 'package:flutter_swiper/flutter_swiper.dart';

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State {
  List _swiperUrlList = [
    "https://ss0.bdstatic.com/94oJfD_bAAcT8t7mm9GUKT-xh_/timg?image&quality=100&size=b4000_4000&sec=1591004658&di=57f566d206833a8645c53f86b550b1b5&src=http://img8.zol.com.cn/bbs/upload/19129/19128997.jpg",
    "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1591014741937&di=5705994c6e0dfc13210e14d4d7a39a12&imgtype=0&src=http%3A%2F%2Fimg.pconline.com.cn%2Fimages%2Fupload%2Fupc%2Ftx%2Fsoftbbs%2F1001%2F14%2Fc0%2F2738706_1263465972689_1024x1024.jpg",
    "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1591014741937&di=0f646d424312e16ff8eadffdbd1e96e9&imgtype=0&src=http%3A%2F%2Fimg8.zol.com.cn%2Fbbs%2Fupload%2F21909%2F21908582.jpg"
  ];
  double _appBarAlpha = 0.0;

  @override
  Widget build(BuildContext context) {
    final PageController _controller = PageController(initialPage: 0);
    return Scaffold(
        body: MediaQuery.removePadding(
      removeTop: true,
      context: context,
      child: Stack(
        children: [
          NotificationListener(
              onNotification: (scrollNotification) {
                if (scrollNotification is ScrollUpdateNotification &&
                    scrollNotification.depth == 0) {
                  _onscroll(scrollNotification.metrics.pixels);
                }
              },
              child: ListView(
                children: [
                  Container(
                    height: 160,
                    child: Swiper(
                      itemCount: _swiperUrlList.length,
                      autoplay: true,
                      itemBuilder: (BuildContext context, int index) {
                        return Image.network(
                          _swiperUrlList[index],
                          fit: BoxFit.fill,
                        );
                      },
                      pagination: SwiperPagination(),
                    ),
                  ),
                  Container(
                    height: 1200,
                    child: ListTile(
                      title: Text("我是内容撑大组件，这里是为了撑大ListView，可以实现上滑ListView查看透明度的变化"),
                    ),
                  )
                ],
              )),
          Opacity(
            opacity: this._appBarAlpha,
            child: Container(
              height: 80,
              decoration: BoxDecoration(
                color: Colors.white,
              ),
              child: Center(
                child: Padding(
                  padding: EdgeInsets.only(top: 20),
                  child: Text("首页"),
                ),
              ),
            ),
          )
        ],
      ),
    ));
  }

  _onscroll(offset) {
    double alpha = offset / 100;
    if (alpha < 0.0){
      alpha = 0.0;
    }
    if (alpha > 1.0){
      alpha = 1.0;
    }
    setState(() {
      this._appBarAlpha = alpha;
    });
  }
}

MediaQuery.removePadding 当ListView作为页面根节点的时候，它与屏幕的最上面有一个状态栏的高度，这时候就需要MediaQuery.removePadding 组件包裹，设置MediaQuery.removePadding 距离最顶端没有距离

if (scrollNotification is ScrollUpdateNotification && scrollNotification.depth == 0)
第一个条件是，如果接收到的通知是ScrollView更新的通知
第二个条件是，如果是最下层的ScrollView（这里的层级与iOS的层级基本一致，最先添加到页面上的控件的层级数为0以后依次递增）

Stack 组件，可以理解为绝对定位，所有被Stack组件包裹的组件，都是以Stack组件的左上角作为起始位置，所以当Stack组件包裹ListView和Container的时候，两个组件是互相重叠并遮盖的效果

Opacity组件，这是一个可以调节透明度的组件，凡是被Opacity组件包裹的子组件，它的透明度都是跟随Opacity的透明度来显示的