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顶部滑动渐变   和  顶部导航 ```pythonimport 'package:flutter/material.dart';import 'package:flutter_swiper/flutter_swiper.dart';import 'package:flutter_screenutil/flutter_screenutil.dart';const APPBAR_SCORLL_OFFSET =100;class HomePage extends StatefulWidget {  @override  _HomePageState createState() => _HomePageState();}class _HomePageState extends State
   
     {  List _imageUrls = [    'https://qnwww2.autoimg.cn/newsdfs/g26/M09/39/1A/autohomecar__ChsEnF3LyfyAPLEOAAPPcEtAcsc635.jpg',    'https://img2.autoimg.cn/admdfs/g1/M04/0C/D7/ChsEmV236AWAeVxxAADNmEFdNug314.jpg',    'https://qnwww2.autoimg.cn/newsdfs/g25/M03/94/0C/autohomecar__ChsEel3Lcj6Ab6fcAAXx3D2fNSg287.jpg',    'https://qnwww2.autoimg.cn/newsdfs/g1/M09/4F/91/autohomecar__ChsEj13LyA6AVsDHAAexjI07sWo824.jpg'  ];  // 定义透明度的变量  double appBarAlpha = 0;    _onScroll(offset) {    double alpha = offset/APPBAR_SCORLL_OFFSET;    if(alpha<0){      alpha = 0;    }else if(alpha > 1){      alpha = 1;    }        setState(() {      appBarAlpha = alpha;    });      }  @override  Widget build(BuildContext context) {    ScreenUtil.instance = ScreenUtil(width: 750,height: 1334)..init(context);    return Scaffold(        body: Stack(      children: 
    
     [        MediaQuery.removePadding(            removeTop: true,            context: context,            child: NotificationListener(              onNotification: (scrollNotification) {                if (scrollNotification is ScrollUpdateNotification &&                    scrollNotification.depth == 0) {                  // 滚动且列表滚动的时候                  _onScroll(scrollNotification.metrics.pixels);                }              },              child: ListView(                children: 
     
      [                  Container(                    /**                     * 在需要的页面使用 屏幕适配                     */                    width: ScreenUtil().setWidth(750),                    height: ScreenUtil().setHeight(400),                    child: Swiper(                      itemCount: _imageUrls.length,                      autoplay: true,                      itemBuilder: (BuildContext context, int index) {                        return Image.network(                          _imageUrls[index],                          fit: BoxFit.cover,                        );                      },                      pagination: SwiperPagination(),                    ),                  ),                  Container(                    height: 800.0,                    child: ListTile(                      title: Text('哈哈'),                    ),                  )                ],              ),            )),            Opacity(              opacity:appBarAlpha,              child: Container(                height: 60,                decoration: BoxDecoration(                  color: Colors.white                ),                child: Center(                  child: Padding(                    padding: EdgeInsets.only(top:20),                    child: Text('首页'),                  ),                ),              ),            )      ],    ));  }}
     
    
   

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