Flutter实战视频-移动电商-16.补充_保持页面状态

16.补充_保持页面状态

修正一个地方:

设置了item的高度为380

横向列表为380、最终build的高度也增加了50为430.

增加了上面的高度以后，下面那个横线划掉的价格可以显示出来了。

但是还是有超出的问题。

保持首页页面状态

每次点击底部的tab标签。再点击首页，首页的数据就会重新加载。

这里就用到了混入，在页面上进行混入：with AutomaticKeepAliveClientMixin

混入之后必须主要三点：

第一，添加混入

第二:重写wantKeepAlive方法，返回为true

第三，改造indexPage

改造indexPage

最终body里面返回的是：IndexedStack

参数1是索引值就是当前的索引

第二个children因为类型是widget类型的数组 所以改造了tabBodies这个List对象为Widget类型的

改造之后的

homePage页面重写initState方法 打印出来一句话，来判断当前的页面是否加载了数据

效果展示

从别的tab切回来，页面状态就保持住了

最终代码

import 'package:flutter/material.dart';
import '../service/service_method.dart';
import 'package:flutter_swiper/flutter_swiper.dart';
import 'dart:convert';
import 'package:flutter_screenutil/flutter_screenutil.dart';
import 'package:url_launcher/url_launcher.dart';

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

class _HomePageState extends State<HomePage> with AutomaticKeepAliveClientMixin{

  @override
  bool get wantKeepAlive => true;

  @override
  void initState() {
    super.initState();
    print('');
  }

  String homePageContent='正在获取数据';
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('百姓生活+')),
      body: FutureBuilder(
        future: getHomePageContent(),
        builder: (context, snapshot) {
          if(snapshot.hasData){
            var data=json.decode(snapshot.data.toString());
            List<Map> swiper=(data['data']['slides'] as List).cast();
            List<Map> navigatorList=(data['data']['category'] as List).cast();
            String adPicture=data['data']['advertesPicture']['PICTURE_ADDRESS'];
            String leaderImage=data['data']['shopInfo']['leaderImage'];
            String leaderPhone=data['data']['shopInfo']['leaderPhone'];
            List<Map> recommendList=(data['data']['recommend'] as List).cast();

            return SingleChildScrollView(
              child: Column(
                children: <Widget>[
                  SwiperDiy(swiperDateList: swiper),
                  TopNavigator(navigatorList:navigatorList ,),
                  AdBanner(adPicture:adPicture),
                  LeaderPhone(leaderImage: leaderImage,leaderPhone: leaderPhone,),
                  Recommend(recommendList:recommendList)
                ],
              ),
            );
          }else{
            return Center(child: Text('加载中....'));
          }
        },
      ),
    );
  }
}
//首页轮播插件
class SwiperDiy extends StatelessWidget {
  final List swiperDateList;
  //构造函数
  SwiperDiy({this.swiperDateList});

  @override
  Widget build(BuildContext context) {

    // print('设备的像素密度：${ScreenUtil.pixelRatio}');
    // print('设备的高：${ScreenUtil.screenWidth}');
    // print('设备的宽：${ScreenUtil.screenHeight}');

    return Container(
      height: ScreenUtil().setHeight(),//
      width:ScreenUtil().setWidth(),
      child: Swiper(
        itemBuilder: (BuildContext context,int index){
          return Image.network("${swiperDateList[index]['image']}",fit: BoxFit.fill,);
        },
        itemCount: swiperDateList.length,
        pagination: SwiperPagination(),
        autoplay: true,
      ),
    );
  }
}

class TopNavigator extends StatelessWidget {
  final List navigatorList;

  TopNavigator({Key key, this.navigatorList}) : super(key: key);

  Widget _gridViewItemUI(BuildContext context,item){
    return InkWell(
      onTap: (){print('点击了导航');},
      child: Column(
        children: <Widget>[
          Image.network(item['image'],width: ScreenUtil().setWidth()),
          Text(item['mallCategoryName'])
        ],
      ),
    );
  }
  @override
  Widget build(BuildContext context) {
    if(this.navigatorList.length>){
      this.navigatorList.removeRange(,this.navigatorList.length);//从第十个截取，后面都截取掉
    }
    return Container(
      height: ScreenUtil().setHeight(),//只是自己大概预估的一个高度，后续可以再调整
      padding: EdgeInsets.all(3.0),//为了不让它切着屏幕的边缘，我们给它一个padding
      child: GridView.count(
        crossAxisCount: ,//每行显示5个元素
        padding: EdgeInsets.all(5.0),//每一项都设置一个padding，这样他就不挨着了。
        children: navigatorList.map((item){
          return _gridViewItemUI(context,item);
        }).toList(),
      ),
    );
  }
}

class AdBanner extends StatelessWidget {
  final String adPicture;

  AdBanner({Key key, this.adPicture}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Image.network(adPicture),
    );
  }
}

//店长电话模块
class LeaderPhone extends StatelessWidget {
  final String leaderImage;//店长图片
  final String leaderPhone;//店长电话 

  LeaderPhone({Key key, this.leaderImage,this.leaderPhone}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: InkWell(
        onTap: _launchURL,
        child: Image.network(leaderImage),
      ),
    );
  }

  void _launchURL() async {
    String url = 'tel:'+leaderPhone;
    //String url = 'http://jspang.com';
    if(await canLaunch(url)){
      await launch(url);
    }else{
      throw 'url不能进行访问，异常';
    }
  }
}

//商品推荐
class Recommend extends StatelessWidget {
  final List recommendList;

  Recommend({Key key, this.recommendList}) : super(key: key);

  //商品标题
  Widget _titleWidget(){
    return Container(
      alignment: Alignment.centerLeft,//局长靠左对齐
      padding: EdgeInsets.fromLTRB(10.0, 2.0, , 5.0),//左上右下
      decoration: BoxDecoration(
        color: Colors.white,
        border: Border(
          bottom: BorderSide(width: 0.5,color: Colors.black12) //设置底部的bottom的边框，Black12是浅灰色
        ),
      ),
      child: Text(
        '商品推荐',
        style:TextStyle(color: Colors.pink)
      ),
    );
  }
  //商品单独项方法
  Widget _item(index){
    return InkWell(
      onTap: (){},//点击事件先留空
      child: Container(
        height: ScreenUtil().setHeight(),//兼容性的高度 用了ScreenUtil
        width: ScreenUtil().setWidth(),//750除以3所以是250
        padding: EdgeInsets.all(8.0),
        decoration: BoxDecoration(
          color: Colors.white,
          border: Border(
            left: BorderSide(width: ,color: Colors.black12)//右侧的 边线的样式 宽度和 颜色
          )
        ),
        child: Column(
          children: <Widget>[
            Image.network(recommendList[index]['image']),
            Text('￥${recommendList[index]['mallPrice']}'),
            Text(
              '￥${recommendList[index]['price']}',
              style: TextStyle(
                decoration: TextDecoration.lineThrough,//删除线的样式
                color: Colors.grey//浅灰色
              ),
            ),
          ],
        ),
      ),
    );
  }
  //横向列表方法
  Widget _recommendList(){
    return Container(
      height: ScreenUtil().setHeight(),
      child: ListView.builder(
        scrollDirection: Axis.horizontal,//横向的
        itemCount: recommendList.length,
        itemBuilder: (context,index){
          return _item(index);
        },
      ),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      height: ScreenUtil().setHeight(),//列表已经设置为330了因为还有上面标题，所以要比330高，这里先设置为380
      margin: EdgeInsets.only(top: 10.0),
      child: Column(
       children: <Widget>[
          _titleWidget(),
          _recommendList()
       ],
      ),
    );
  }
}

home_page.dart

import 'package:flutter/material.dart';
import 'package:flutter/cupertino.dart';
import 'home_page.dart';
import 'category_page.dart';
import 'cart_page.dart';
import 'member_page.dart';
import 'package:flutter_screenutil/flutter_screenutil.dart';

class IndexPage extends StatefulWidget {
  @override
  _IndexPageState createState() => _IndexPageState();
}

class _IndexPageState extends State<IndexPage> {
  final List<BottomNavigationBarItem> bottomTabs=[
    BottomNavigationBarItem(
      icon:Icon(CupertinoIcons.home),//这里使用IOS风格的
      title: Text('首页')
    ),
    BottomNavigationBarItem(
      icon:Icon(CupertinoIcons.search),
      title: Text('分类')
    ),
    BottomNavigationBarItem(
      icon:Icon(CupertinoIcons.shopping_cart),
      title: Text('购物车')
    ),
    BottomNavigationBarItem(
      icon:Icon(CupertinoIcons.profile_circled),
      title: Text('会员中心')
    )
  ];
  final List<Widget> tabBodies=[
    HomePage(),
    CategoryPage(),
    CartPage(),
    MemberPage()
  ];

  int currentIndex=;//当前索引
  var currentPage;
 @override
  void initState() {
    currentPage=tabBodies[currentIndex];//默认页面数组内索引值为0的页面
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
     ScreenUtil.instance = ScreenUtil(width: ,height: )..init(context);

    return Scaffold(
      backgroundColor: Color.fromRGBO(, , , 1.0),//颜色固定死，比白色稍微灰一点
      bottomNavigationBar: BottomNavigationBar(
        type:BottomNavigationBarType.fixed,
        currentIndex: currentIndex,//当前索引值
        items: bottomTabs,
        onTap: (index){
          setState(() {
           currentIndex=index;
           currentPage=tabBodies[currentIndex];
          });
        },
      ),
      body: IndexedStack(
        index: currentIndex,
        children: tabBodies,
      ),
    );
  }
}

index_page.dart

超出边界的错误

I/flutter ( 6079): ══╡ EXCEPTION CAUGHT BY RENDERING LIBRARY ╞═════════════════════════════════════════════════════════
I/flutter ( 6079): The following message was thrown during layout:
I/flutter ( 6079): A RenderFlex overflowed by 2.9 pixels on the bottom.
I/flutter ( 6079):
I/flutter ( 6079): The overflowing RenderFlex has an orientation of Axis.vertical.
I/flutter ( 6079): The edge of the RenderFlex that is overflowing has been marked in the rendering with a yellow and
I/flutter ( 6079): black striped pattern. This is usually caused by the contents being too big for the RenderFlex.
I/flutter ( 6079): Consider applying a flex factor (e.g. using an Expanded widget) to force the children of the
I/flutter ( 6079): RenderFlex to fit within the available space instead of being sized to their natural size.
I/flutter ( 6079): This is considered an error condition because it indicates that there is content that cannot be
I/flutter ( 6079): seen. If the content is legitimately bigger than the available space, consider clipping it with a
I/flutter ( 6079): ClipRect widget before putting it in the flex, or using a scrollable container rather than a Flex,
I/flutter ( 6079): like a ListView.
I/flutter ( 6079): The specific RenderFlex in question is:
I/flutter ( 6079):   RenderFlex#907c5 relayoutBoundary=up17 OVERFLOWING
I/flutter ( 6079):   creator: Column ← ConstrainedBox ← Padding ← Container ← Recommend ← Column ← _SingleChildViewport
I/flutter ( 6079):   ← IgnorePointer-[GlobalKey#ecea8] ← Semantics ← Listener ← _GestureSemantics ←
I/flutter ( 6079):   RawGestureDetector-[LabeledGlobalKey<RawGestureDetectorState>#92ff4] ← ⋯
I/flutter ( 6079):   parentData: <none> (can use size)
I/flutter ( 6079):   constraints: BoxConstraints(0.0<=w<=411.4, h=220.3)
I/flutter ( 6079):   size: Size(411.4, 220.3)
I/flutter ( 6079):   direction: vertical
I/flutter ( 6079):   mainAxisAlignment: start
I/flutter ( 6079):   mainAxisSize: max
I/flutter ( 6079):   crossAxisAlignment: center
I/flutter ( 6079):   verticalDirection: down
I/flutter ( 6079): ◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤◢◤

群里面也有遇到这个问题的：先自己解决，不行可以问问这个人

2019年4月8日-wjw

我以为是SingleChildScrollView引起的这个问题，所以去掉了这个SingleChildScrollView，还是用直接Column，发现还是不行，黄条显示的更多了。

不起作用，恢复原来的代码：

修复Recommend商品推荐超出边界的问题

把最终Recommend的build里面的高度本来是430，这里改成了438就可以了。

结束