Flutter 基础-下

一、shared_preferences

• shared_preferences 是一个本地数据缓存库（类似 AsyncStorage）
  • https://pub.dev/packages/shared_preferences
• 使用步骤
  • 在 pubsepc.yaml 中添加 shared_preferences 依赖
  • 安装依赖（pub get | flutter packages get | VS Code 中保存配置，自动下载
  • 引入import ‘package:shared_preferences/shared_preferences.dart’;
  • 使用 SharedPreferences prefs = await SharedPreferences.getInstance();

shared_preferences - 操作

• 增
  • setString(key, value)
• 删
  • remove(key) | clear()
• 改
  • 更改就是重新设置数据setString(key, value)
• 查
  • getString(key)

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("shared_preferences"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: SharedPreferencesDemo()
    );
  }
}

class SharedPreferencesDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      child: Column(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          ElevatedButton(
            onPressed: _incrementCounter, 
            child: Text('递增')
          ),
          ElevatedButton(
            onPressed: _decrementCounter, 
            child: Text('递减')
          ),
          ElevatedButton(
            onPressed: _removeCounter, 
            child: Text('删除')
          ),
          ElevatedButton(
            onPressed: _addMyContent, 
            child: Text('设置字符串')
          ),
          ElevatedButton(
            onPressed: _getMyContent, 
            child: Text('获取字符串')
          ),
          ElevatedButton(
            onPressed: _clearContent, 
            child: Text('清空')
          ),
        ],
      )
    );
  }

  _incrementCounter() async {
    // 获取保存实例
    SharedPreferences prefs = await SharedPreferences.getInstance();
    int counter = (prefs.getInt('counter') ?? 0) + 1;
    print('Pressed $counter times.');
    await prefs.setInt('counter', counter);
  }

  _decrementCounter() async {
    // 获取保存实例
    SharedPreferences prefs = await SharedPreferences.getInstance();
    int counter = prefs.getInt('counter') ?? 0;
    if (counter > 0) {
      counter--;
    }
    print('Pressed $counter times.');
    await prefs.setInt('counter', counter);
  }

  _removeCounter() async {
    // 获取保存实例
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.remove('counter');
    int counter = (prefs.getInt('counter') ?? 0) + 1;
    print('Pressed $counter times.');
  }

  _addMyContent() async {
    // 获取保存实例
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.setString('hi', 'Hello World');
    String content = prefs.getString('hi') ?? "";
    print('设置字符串的内容是 $content');
  }

  _getMyContent() async {
    // 获取保存实例
    SharedPreferences prefs = await SharedPreferences.getInstance();
    String content = prefs.getString('hi') ?? "";
    print('获取字符串的内容是 $content');
  }

  _clearContent() async {
    // 获取保存实例
    SharedPreferences prefs = await SharedPreferences.getInstance();
    await prefs.clear();
  }
}

二、StatefulWidget

StatefulWidget

• Flutter 中的组件，按状态划分
  • StatelessWidget （无状态组件）
  • StatefulWidget（状态组件）
• 按状态作用域划分
  • 组件内私有状态（StatefulWidget)
  • 跨组件状态共享（InheritedWidget、 Provider）
  • 全局状态（Redux | fish-redux、Mobx…
• 状态组件的组成
  • StatefulWidget(组件本身不可变 - @immutable)
  • State（将变化的状态放到 State 中维护）

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("StatefulWidget"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: MyState()
    );
  }
}

class MyState extends StatefulWidget {
  @override
  _MyStateState createState() => _MyStateState();
}

class _MyStateState extends State<MyState> {
  int _num = 0;

  void _increment() {
    setState(() {
      _num++;
    });
  }

  void _decrement() {
    setState(() {
      _num--;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: [
          ElevatedButton(
            onPressed: _decrement, 
            child: Text('-')
          ),
          Padding(
            padding: EdgeInsets.all(20),
            child: Text('$_num')
          ),
          ElevatedButton(
            onPressed: _increment, 
            child: Icon(Icons.add)
          )
        ],
      )
    );
  }
}

三、DataTable

• DataTable 是 Flutter 中的表格
  • columns (声明表头列表)
    • DataColumn (表头单元格)
• rows (声明数据列表)
  • DataRow (一行数据)
    • DataCell (数据单元格）
• 其他属性

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("DataTable"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: UserList()
    );
  }
}

class User {
  String name;
  int age;
  bool selected;

  User(this.name, this.age, {this.selected = false});
}

class UserList extends StatefulWidget {
  UserList({Key key}) : super(key: key);

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

class _UserListState extends State<UserList> {
  List<User> data = [
    User('张三', 18),
    User('张三丰', 218, selected: true),
    User('张翠山', 30),
    User('张无忌', 60),
  ];

  var _sortAscending = true;

  List _getUserRows() {
    List<DataRow> dataRows = [];
    for (int i = 0; i < data.length; i++) {
      dataRows.add(
        DataRow(
          selected: data[i].selected,
          onSelectChanged: (selected) {
            setState(() {
              data[i].selected = selected;
            });
          },
          cells: [
            DataCell(Text('${data[i].name}')),
            DataCell(Text('${data[i].age}')),
            DataCell(Text('男')),
            DataCell(Text('---')),
          ]
        )
      );
    }

    return dataRows;
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      child: SingleChildScrollView(
        scrollDirection: Axis.horizontal,
        child: DataTable(
          sortColumnIndex: 1,
          sortAscending: _sortAscending,
          dataRowHeight: 100,
          horizontalMargin: 20,
          columnSpacing: 100,
          columns: [
            DataColumn(label: Text('姓名')),
            DataColumn(
              label: Text('年龄'),
              numeric: true,
              onSort: (int columnIndex, bool asscending) {
                setState(() {
                  _sortAscending = asscending;
                  if (asscending) {
                    data.sort((a, b) => a.age.compareTo(b.age));
                  } else {
                    data.sort((a, b) => b.age.compareTo(a.age));
                  }
                });
              }
            ),
            DataColumn(label: Text('性别')),
            DataColumn(label: Text('简介')),
          ], 
          rows: _getUserRows(),
          // [
          //   DataRow(
          //     cells: [
          //       DataCell(Text('张三')),
          //       DataCell(Text('18')),
          //       DataCell(Text('男')),
          //       DataCell(Text('一个男人')),
          //     ]
          //   ),
          //   DataRow(
          //     cells: [
          //       DataCell(Text('张三')),
          //       DataCell(Text('18')),
          //       DataCell(Text('男')),
          //       DataCell(Text('一个男人')),
          //     ]
          //   ),
          //   DataRow(
          //     cells: [
          //       DataCell(Text('张三')),
          //       DataCell(Text('18')),
          //       DataCell(Text('男')),
          //       DataCell(Text('一个男人')),
          //     ]
          //   )
          // ]
        )
      ),
    );
  }
}

四、InheritedWidget

• What：提供了沿树向下，共享数据的功能
  • 即子组件可以获取父组件(InheritedWidget的子类)的数据
• Why:
  • 依赖构造函数传递数据的方式不能满足业务需求
  • 所以，需要一个新的，更好的跨组件数据传输方案
• How:
  • BuildContext.dependOnInheritedWidgetOfExactType()

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("InheritedWidget"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: MyState()
    );
  }
}

class MyState extends StatefulWidget {
  @override
  _MyStateState createState() => _MyStateState();
}

class _MyStateState extends State<MyState> {
  int _num = 0;

  void _increment() {
    setState(() {
      _num++;
    });
  }

  void _decrement() {
    setState(() {
      _num--;
    });
  }

  @override
  Widget build(BuildContext context) {
    return ShareDataWidget(
      num: _num,
      child: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: _decrement, 
              child: Text('-')
            ),
            Padding(
              padding: EdgeInsets.all(20),
              // child: Text('$_num')
              // 跨组件访问数据
              child: MyCounter(),
            ),
            ElevatedButton(
              onPressed: _increment, 
              child: Icon(Icons.add)
            )
          ],
        )
      ),
    );
  }
}

class MyCounter extends StatefulWidget {
  MyCounter({Key key}) : super(key: key);

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

class _MyCounterState extends State<MyCounter> {
  @override
  Widget build(BuildContext context) {
    // 使用 InheritedWidget 中的共享数据
    return Text(ShareDataWidget.of(context).num.toString());
  }
}

// 数据共享组件
class ShareDataWidget extends InheritedWidget {
  final int num;
  final Widget child;

  ShareDataWidget({Key key, this.child, @required this.num}) : super(key: key, child: child);

  static ShareDataWidget of(BuildContext context) {
    return context.dependOnInheritedWidgetOfExactType<ShareDataWidget>();
  }

  @override
  bool updateShouldNotify(ShareDataWidget oldWidget) {
    return true;
  }
}

五、生命周期

• initState() 组件对象插入到元素树中时
• didChangeDependencies() 当前状态对象的依赖改变时
• build() 组件渲染时
• setState() 组件对象的内部状态变更时
• didUpdateWidget() 组件配置更新时
• deactivate() 组件对象在元素树中暂时移除时
• dispose() 组件对象在元素树中永远移除时

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Life Cycle"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: MyState()
    );
  }
}

class MyState extends StatefulWidget {
  @override
  // _MyStateState createState() => _MyStateState();
  _MyStateState createState() {
    print('create state');
    return _MyStateState();
  }
}

class _MyStateState extends State<MyState> {
  int _num;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    print('init state');
    _num = 1;
  }

  @override
  void didChangeDependencies() {
    // TODO: implement didChangeDependencies
    super.didChangeDependencies();
    print('didChangeDependencies');
  }

  @override
  void didUpdateWidget(covariant MyState oldWidget) {
    // TODO: implement didUpdateWidget
    super.didUpdateWidget(oldWidget);
    print('didUpdateWidget');
  }

  @override
  void deactivate() {
    // TODO: implement deactivate
    super.deactivate();
    print('deactivate');
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    print('dispose');
  }

  void _increment() {
    setState(() {
      print('setState');
      _num++;
    });
  }

  void _decrement() {
    setState(() {
      print('setState');
      _num--;
    });
  }

  @override
  Widget build(BuildContext context) {
    print('build');
    return Center(
      child: Column(
        children: [
          ElevatedButton(
            onPressed: _decrement, 
            child: Text('-')
          ),
          Padding(
            padding: EdgeInsets.all(20),
            child: Text('$_num')
          ),
          ElevatedButton(
            onPressed: _increment, 
            child: Icon(Icons.add)
          )
        ],
      )
    );
  }
}

六、Provider

• Provider 是对 InheritedWidget 的封装
  • https://pub.dev/packages/provider
• 优点：
  • 简化资源的分配与处置
  • 懒加载

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // 2. 创建 Provider （注册数据模型）
    return ChangeNotifierProvider(
      create: (BuildContext context) => new LikesModel(),
      child: Scaffold(
        appBar: AppBar(
          title: Text("Provider"),
          leading: Icon(Icons.menu),
          actions: [
            Icon(Icons.settings)
          ],
          elevation: 0.0,
          centerTitle: true,
        ),
        body: MyHomePage()
      ),
    );
  }
}

// 1. 创建数据模型
class LikesModel extends ChangeNotifier {
  int _counter = 0;

  int get counter => _counter;

  incrementCounter() {
    // 累加
    _counter++;

    // 通过 UI 更新
    notifyListeners();
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      width: double.infinity,
      child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          // 3. 在子组件中使用数据模型
          Text(
            '${context.watch<LikesModel>().counter}'
          ),
          TextButton(
            // 3. 在子组件中使用数据模型
            onPressed: Provider.of<LikesModel>(context).incrementCounter, 
            child: Icon(Icons.thumb_up)
          )
        ],
      ),
    );
  }
}

七、匿名路由

路由简介

• Route
  • 一个路由是一个屏幕或页面的抽象
• Navigator
  • 管理路由的组件。Navigator 可以通过路由入栈和出栈来实现页面之间的跳转
  • 常用属性：
    • initialRoute：初始路由，即默认页面
    • onGenerateRoute: 动态路由（根据规则，匹配动态路由
    • onUnknownRoute: 未知路由，也就是 404
    • routes： 路由集合

匿名路由

• Navigator
• push （跳转到指定组件）

Navigator.push(
context,
MaterialPageRoute(builder: (context) => 组件名称（))

• pop (回退)

 Navigator.pop(context)

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("匿名路由"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: HomePage()
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: ElevatedButton(
          onPressed: () {
            return Navigator.push(
              context, 
              MaterialPageRoute(builder: (context) => Product())
            );
          }, 
          child: Text('跳转到商品页面'),
        )
      ),
    );
  }
}

class Product extends StatelessWidget {
  const Product({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("商品页面"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Container(
        child: Center(
          child: ElevatedButton(
            onPressed: () => Navigator.pop(context), 
            child: Text('返回')
          )
        ),
      ),
    );
  }
}

八、命名路由

• 声明路由

  • routes 路由表（Map 类型）
  • initialRoute（初始路由）
  • onUnknownRoute（未知路由-404)

• 跳转到命名路由

  • Navigator.pushNamed(context,‘路由名称");

  
  main.dart

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Flutter Demo",
      home: Home(),
      // 声明命名路由
       routes: {
         'home': (context) => Home(),
         'product': (context) => Product(),
         'productDetail': (context) => ProductDetail(),
       },
      initialRoute: 'home',
      theme: CustomTheme.lightTheme,
      darkTheme: CustomTheme.darkTheme,

      debugShowCheckedModeBanner: false,
      // 国际化
      localizationsDelegates: [
        // 本地化代理
        CustomLocalizations.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],
      supportedLocales: [
        const Locale('en', 'US'), // 美国英语
        const Locale('zh', 'CN'), // 简体中文
      ],
      localeResolutionCallback: (locale, supportedLocales) {
        print('deviceLocale: $locale');
        print('languageCode: ${locale.languageCode}');
        print('countryCode: ${locale.countryCode}');
        for (var supportedLocale in supportedLocales) {
          if (supportedLocale.languageCode == locale.languageCode 
          && supportedLocale.countryCode == locale.countryCode) {
            return supportedLocale;
          }
        }

        return supportedLocales.first;
      },
    );
  }

_namedRoute.dart

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("首页"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () => Navigator.pushNamed(context, 'product'), 
              child: Text('跳转'),
            ),
            ElevatedButton(
              onPressed: () => Navigator.pushNamed(context, 'user'), 
              child: Text('未知路由'),
            ),
          ],
        ),
      ),
    );
  }
}

class Product extends StatelessWidget {
  const Product({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("商品页"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () => Navigator.pop(context), 
              child: Text('返回'),
            )
          ],
        ),
      ),
    );
  }
}

class UnknowPage extends StatelessWidget {
  const UnknowPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("404"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () => Navigator.pop(context), 
              child: Text('返回'),
            )
          ],
        ),
      ),
    );
  }
}

九、动态路由

• 动态路由是指，通过onGenerateRoute属性指定的路由

main.dart

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("首页"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () => Navigator.pushNamed(context, '/product'), 
              child: Text('跳转'),
            ),
            ElevatedButton(
              onPressed: () => Navigator.pushNamed(context, '/product/1'), 
              child: Text('商品1'),
            ),
            ElevatedButton(
              onPressed: () => Navigator.pushNamed(context, '/product/2'), 
              child: Text('商品2'),
            ),
            ElevatedButton(
              onPressed: () => Navigator.pushNamed(context, 'user'), 
              child: Text('未知路由'),
            ),
          ],
        ),
      ),
    );
  }
}

class Product extends StatelessWidget {
  const Product({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("商品页"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () => Navigator.pop(context), 
              child: Text('返回'),
            )
          ],
        ),
      ),
    );
  }
}

class ProductDetail extends StatelessWidget {
  // product/1
  final String id;

  const ProductDetail({Key key, this.id}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("商品详情页"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            Text('当前商品的id是：'+this.id),
            ElevatedButton(
              onPressed: () => Navigator.pop(context), 
              child: Text('返回'),
            )
          ],
        ),
      ),
    );
  }
}

class UnknowPage extends StatelessWidget {
  const UnknowPage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("404"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          children: [
            ElevatedButton(
              onPressed: () => Navigator.pop(context), 
              child: Text('返回'),
            )
          ],
        ),
      ),
    );
  }
}

十、路由传参-匿名路由

• 路由中声明参数

  • Navigator.push
    

• 组件中接收参数

路由传参-命名路由

• 路由中声明参数
  • Navigator.pushNamed(context, routename, {arguments})
• 组件中接收参数
  • ModalRoute.of(context).settings.arguments
    

十一、Drawer 导航

• Scaffold
  • drawer （左侧抽屉菜单）
  • endDrawer (右侧抽屉菜单)
• UserAccountsDrawerHeader
  • 抽屉菜单头部组件
• AboutListTile
  • 关于弹窗

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Drawer"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: HomePage(),
      drawer: DrawerList(),
      endDrawer: DrawerList(),
    );
  }
}

class HomePage extends StatelessWidget {
  const HomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      child: Center(
        child: Text('Home'),
      ),
    );
  }
}

class DrawerList extends StatelessWidget {
  const DrawerList({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Drawer(
      child: ListView(
        padding: EdgeInsets.all(0),
        children: [
          UserAccountsDrawerHeader(
            accountName: Text('初六'),
            accountEmail: Text('[email protected]'),
            decoration: BoxDecoration(
              image: DecorationImage(
                image: AssetImage('images/bg1.jpg'),
                fit: BoxFit.cover,
              )
            ),
            currentAccountPicture: CircleAvatar(
              backgroundImage: AssetImage('images/flutter.jpg'),
            ),
          ),
          ListTile(
            leading: Icon(Icons.settings),
            title: Text('设置'),
            trailing: Icon(Icons.arrow_forward_ios),
          ),
          Divider(thickness: 2,),
          ListTile(
            leading: Icon(Icons.account_balance),
            title: Text('余额'),
            trailing: Icon(Icons.arrow_forward_ios),
          ),
          Divider(thickness: 2,),
          ListTile(
            leading: Icon(Icons.person),
            title: Text('我的'),
            trailing: Icon(Icons.arrow_forward_ios),
          ),
          Divider(thickness: 2,),
          ListTile(
            leading: Icon(Icons.person),
            title: Text('回退'),
            onTap: () => Navigator.pop(context),
            trailing: Icon(Icons.arrow_forward_ios),
          ),
          AboutListTile(
            child: Text('关于'),
            applicationName: "你的应用名称",
            applicationVersion: "1.0.0",
            icon: CircleAvatar(
              child: Text('aaa')
            ),
            applicationLegalese: "应用法律条例",
            aboutBoxChildren: [
              Text('条例一：xxxx'),
              Text('条例二：xxxx'),
            ],
            applicationIcon: Image.asset(
              'images/flutter.jpg',
              width: 50,
              height: 50,
            )
          ),
          // Text('Drawer')
        ]
      ),
    );
  }
}

十二、BottomNavigationBar 导航

• items
  • 包含导航（BottomNavigationBarltem）的列表
• currentIndex
  • 当前导航索引
• type
  • 导航类型（BottomNavigationBarType)
• onTap()
  • 导航的点击事件（一般会更新导航索引)

import 'package:flutter/material.dart';

class Home extends StatefulWidget {
  Home({Key key}) : super(key: key);

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

class _HomeState extends State<Home> {
  final List<BottomNavigationBarItem> bottomNavItems = [
    BottomNavigationBarItem(
      backgroundColor: Colors.blue,
      icon: Icon(Icons.home),
      label: '首页',
    ),
    BottomNavigationBarItem(
      backgroundColor: Colors.green,
      icon: Icon(Icons.message),
      label: '消息',
    ),
    BottomNavigationBarItem(
      backgroundColor: Colors.amber,
      icon: Icon(Icons.shopping_cart),
      label: '购物车',
    ),
    BottomNavigationBarItem(
      backgroundColor: Colors.red,
      icon: Icon(Icons.person),
      label: '我',
    ),
  ];

  final pages = [
    Center(
      child: Text("Home", style: TextStyle(fontSize: 50)),
    ),
    Center(
      child: Text("Message", style: TextStyle(fontSize: 50)),
    ),
    Center(
      child: Text("Cart", style: TextStyle(fontSize: 50)),
    ),
    Center(
      child: Text("Profile", style: TextStyle(fontSize: 50)),
    ),
  ];

  int currentIndex;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    currentIndex = 0;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("底部导航"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: bottomNavItems,
        currentIndex: currentIndex,
        type: BottomNavigationBarType.fixed,
        // type: BottomNavigationBarType.shifting,
        onTap: (index) {
          _changePage(index);
        }
      ),
      body: pages[currentIndex],
    );
  }

  void _changePage(int index) {
    if (index != currentIndex) {
      setState(() {
        currentIndex = index;
      });
    }
  }
}

十三、Tab 导航

• DefaultTabController (整个Tab导航的容器)
  • length (声明导航数量)
  • child（指定子组件）
• TabBar (导航菜单)
  • tabs （导航菜单数组）
• TabBarView (导航页面)
  • children (多个导航页面内容)

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  // 菜单数组
  final List<Widget> _tabs = [
    Tab(text: "首页", icon: Icon(Icons.home)),
    Tab(text: "添加", icon: Icon(Icons.add)),
    Tab(text: "搜索", icon: Icon(Icons.search)),
  ];

  // 页面数组
  final List<Widget> _tabViews = [
    Icon(Icons.home, size: 120, color: Colors.red),
    Icon(Icons.add, size: 120, color: Colors.green),
    Icon(Icons.search, size: 120, color: Colors.black),
  ];

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: _tabs.length, 
      child: Scaffold(
        appBar: AppBar(
          title: Text("Tab"),
          leading: Icon(Icons.menu),
          actions: [
            Icon(Icons.settings)
          ],
          elevation: 0.0,
          centerTitle: true,
          bottom: TabBar(
            tabs: _tabs,
            labelColor: Colors.yellow,
            unselectedLabelColor: Colors.black45,
            indicatorSize: TabBarIndicatorSize.tab,
            indicatorColor: Colors.yellow,
            indicatorWeight: 10,
          ),
        ),
        body: TabBarView(
          children: _tabViews
        ),
        bottomNavigationBar: TabBar(
          tabs: _tabs,
          labelColor: Colors.blue,
          unselectedLabelColor: Colors.black45,
        ),
      ),
    );
  }
}

十四、表单-Switch

• value（开关的值，一般与状态字段绑定）
  • onChanged（开关状态变更时调用)
  • activeColor (开关开启时的圆圈颜色)
  • activeTrackColor （开关开启时的轨道颜色）
  • inactiveThumbColor (开关关闭时的圆圈颜色)
  • inactiveTrackColor (开关关闭时的轨道颜色)
• CupertinoSwitch (iOS风格的开关)
  • import ‘package:flutter/cupertino.dart’;

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Switch"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: SwitchDemo()
    );
  }
}

class SwitchDemo extends StatefulWidget {
  SwitchDemo({Key key}) : super(key: key);

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

class _SwitchDemoState extends State<SwitchDemo> {
  bool _switchValue = false;

  @override
  Widget build(BuildContext context) {
    return Container(
       child: ListView(
         children: [
           ListTile(
             leading: Switch(
               value: _switchValue,
               onChanged: (bool val) {
                 setState(() {
                   _switchValue = val;
                 });
               },
               activeColor: Colors.orange,
               activeTrackColor: Colors.pink,
               inactiveTrackColor: Colors.grey,
               inactiveThumbColor: Colors.blue[100],
             ),
             title: Text("当前的状态是: ${_switchValue == true ? "选中" : "未选中"}"),
           ),
           ListTile(
             leading: CupertinoSwitch(
               value: _switchValue, 
               onChanged: (bool val) {
                 setState(() {
                   _switchValue = val;
                 });
               },
               activeColor: Colors.red,
               trackColor: Colors.yellow,
             ),
             title: Text('iOS 风格的 Switch'),
           )
         ]
       ),
    );
  }
}

十五、表单-Checkbox

• value（复选框的值）
  • onChanged (复选框状态更改时调用）
  • activeColor （选中时，复选框背景的颜色）
  • checkColor（选中时，复选框中对号的颜色）
• CheckboxListTile
  • title （标题)
  • subtitle （子标题）

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Checkbox"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: CheckboxDemo()
    );
  }
}

class CheckboxDemo extends StatefulWidget {
  CheckboxDemo({Key key}) : super(key: key);

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

class _CheckboxDemoState extends State<CheckboxDemo> {
  bool _male = true;
  bool _female = false;
  bool _transgender = true;
  bool _value1 = true;
  bool _value2 = false;

  @override
  Widget build(BuildContext context) {
    return Column(
       children: [
         ListTile(
           leading: Checkbox(
             value: this._male,
             onChanged: (bool value) {
               setState(() {
                 this._male = value;
               });
             },
           ),
           title: Text('男'),
         ),
         ListTile(
           leading: Checkbox(
             value: this._female,
             onChanged: (bool value) {
               setState(() {
                 this._female = value;
               });
             },
           ),
           title: Text('女'),
         ),
         ListTile(
           leading: Checkbox(
             value: this._transgender,
             onChanged: (bool value) {
               setState(() {
                 this._transgender = value;
               });
             },
             activeColor: Colors.pink,
             checkColor: Colors.yellow,
           ),
           title: Text('人妖'),
         ),
         CheckboxListTile(
           secondary: Icon(Icons.settings, size: 50),
           value: this._value1, 
           onChanged: (bool value) {
            setState(() {
              this._value1 = value;
            });
           },
           title: Text('1:00 叫我起床'),
           subtitle: Text('太困了,起不来'),
           activeColor: Colors.green,
           checkColor: Colors.green,
           selected: this._value1,
         ),
         CheckboxListTile(
           secondary: Icon(Icons.settings, size: 50),
           value: this._value2, 
           onChanged: (bool value) {
            setState(() {
              this._value2 = value;
            });
           },
           title: Text('2:00 叫我起床'),
           subtitle: Text('这还差不多'),
         ),
       ],
    );
  }
}

十六、表单-TextField

• autofocus（是否获取焦点）
• keyboardType (键盘类型)
• obscureText （设置为密码框）
• decoration （样式修饰）
• onChanged (内容更改时自动调用-value)
• labelText (标题)
• hintText(提示文字-placeholder)
• maxLines （显示行数-文本域）

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("TextField"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: TextFieldDemo()
    );
  }
}

class TextFieldDemo extends StatefulWidget {
  TextFieldDemo({Key key}) : super(key: key);

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

class _TextFieldDemoState extends State<TextFieldDemo> {
  String phone;
  String password;
  String description;

  _register() {
    print(phone);
    print(password);
    print(description);
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(20),
       child: Column(
         children: [
           TextField(
             autofocus: true,
             keyboardType: TextInputType.phone,
             decoration: InputDecoration(
               prefixIcon: Icon(Icons.mobile_screen_share),
               // 获取焦点时,高亮的边框样式
               focusedBorder: UnderlineInputBorder(
                 borderSide: BorderSide(
                   color: Colors.green,
                 )
               ),
               // 默认边框样式
               enabledBorder: UnderlineInputBorder(
                 borderSide: BorderSide(
                   color: Colors.yellow,
                 )
               ),
               labelText: "手机号",
               hintText: "请输入手机号",
               hintStyle: TextStyle(
                 color: Colors.green,
                 fontSize: 14,
               ),
             ),
             maxLength: 11,
             onChanged: (value) {
               setState(() {
                 phone = value;
               });
             },
           ),
           TextField(
             obscureText: true,
             keyboardType: TextInputType.text,
             decoration: InputDecoration(
               prefixIcon: Icon(Icons.code_outlined),
               // 获取焦点时,高亮的边框样式
               focusedBorder: UnderlineInputBorder(
                 borderSide: BorderSide(
                   color: Colors.green,
                 )
               ),
               // 默认边框样式
               enabledBorder: UnderlineInputBorder(
                 borderSide: BorderSide(
                   color: Colors.yellow,
                 )
               ),
               labelText: "密码",
               hintText: "请输入密码",
               hintStyle: TextStyle(
                 color: Colors.green,
                 fontSize: 14,
               ),
             ),
             onChanged: (value) {
               setState(() {
                 password = value;
               });
             },
           ),
           TextField(
             maxLines: 5,
             keyboardType: TextInputType.text,
             decoration: InputDecoration(
               prefixIcon: Icon(Icons.person),
               // 获取焦点时,高亮的边框样式
               focusedBorder: UnderlineInputBorder(
                 borderSide: BorderSide(
                   color: Colors.green,
                 )
               ),
               // 默认边框样式
               enabledBorder: UnderlineInputBorder(
                 borderSide: BorderSide(
                   color: Colors.yellow,
                 )
               ),
               labelText: "简介",
               hintText: "请介绍一下自己",
               hintStyle: TextStyle(
                 color: Colors.green,
                 fontSize: 14,
               ),
             ),
             onChanged: (value) {
               setState(() {
                 description = value;
               });
             },
           ),
         
           // 声明按钮
           Container(
             width: double.infinity,
             child: ElevatedButton(
              onPressed: () {
                _register();
              }, 
              child: Text('提交'),
            ),
           )
         ],
       ),
    );
  }
}

十七、表单-日历

• CalendarDatePicker （日历选择器）
  • initialCalendarMode
    • DatePickerMode.day
    • DatePickerMode.year
• showDatePicker （日期选择器）
  • initialDatePickerMode (year | day)
  • initialEntryMode (calendar | input)
• showTimePicker （时间选择器）
  

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Calendar'),
        centerTitle: true,
        elevation: 0.0,
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.search)
        ],
        backgroundColor: Colors.blue,
      ),
      body: CalendarDemo(),
    );
  }
}

class CalendarDemo extends StatefulWidget {
  CalendarDemo({Key key}) : super(key: key);

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

class _CalendarDemoState extends State<CalendarDemo> {
  @override
  Widget build(BuildContext context) {
    return Container(
       child: ListView(
        padding: EdgeInsets.all(15),
        children: [
          _showDatePicker(context),
          _showDatePickerForYear(context),
          _showDatePickerForInput(context),
          _showDatePickerForTheme(context),
          _showTimePicker(context),

          Text("CalendarDatePicker day"),
          SizedBox(height: 30),
          _calendarDatePicker(DatePickerMode.day),
          SizedBox(height: 30),
          Text("CalendarDatePicker year"),
          SizedBox(height: 30),
          _calendarDatePicker(DatePickerMode.year),
          SizedBox(height: 30),
          Text("_cupertinoTimePicker - hms"),
          SizedBox(height: 30),
          _cupertinoTimePicker(CupertinoTimerPickerMode.hms),
          SizedBox(height: 30),
          Text("_cupertinoTimePicker - hm"),
          SizedBox(height: 30),
          _cupertinoTimePicker(CupertinoTimerPickerMode.hm),
          SizedBox(height: 30),
          Text("_cupertinoTimePicker - ms"),
          SizedBox(height: 30),
          _cupertinoTimePicker(CupertinoTimerPickerMode.ms),
          SizedBox(height: 30),
          Text("CupertinoDatePicker - time"),
          SizedBox(height: 30),
          _cupertinoDatePicker(CupertinoDatePickerMode.time),
          SizedBox(height: 30),
          Text("CupertinoDatePicker - dateAndTime"),
          SizedBox(height: 30),
          _cupertinoDatePicker(CupertinoDatePickerMode.dateAndTime),
          SizedBox(height: 30),
          Text("CupertinoDatePicker - date"),
          SizedBox(height: 30),
          _cupertinoDatePicker(CupertinoDatePickerMode.date),
        ],
      ),
    );
  }

  ElevatedButton _showDatePicker(context) {
    return ElevatedButton(
      child: Text("showDatePicker"),
      onPressed: () {
        showDatePicker(
          context: context,
          initialDatePickerMode: DatePickerMode.day, // 日期选择模式，默认为天数选择
          initialDate: DateTime.now(), // 初始化选中日期
          firstDate: DateTime(2020, 6), // 开始日期
          lastDate: DateTime(2021, 6), // 结束日期
          initialEntryMode: DatePickerEntryMode.calendar, // 日历弹框样式

          currentDate: DateTime.now(), // 当前日期
          helpText: "日期选择器", // 左上方提示
          cancelText: "取消",  // 取消按钮文案
          confirmText: "确定",  // 确认按钮文案

          errorFormatText: "errorFormatText",  // 格式错误提示
          errorInvalidText: "errorInvalidText",  // 输入不在 first 与 last 之间日期提示
          fieldLabelText: "fieldLabelText",  // 输入框上方提示
          fieldHintText: "fieldHintText",  // 输入框为空时内部提示
          useRootNavigator: true, // 是否为根导航器
          // 设置不可选日期
          selectableDayPredicate: (dayTime) {
            if (dayTime == DateTime(2021, 1, 15)) {
              return false;
            }
            return true;
          }
        );
      },
    );
  }

  ElevatedButton _showDatePickerForYear(context) {
    return ElevatedButton(
      child: Text("showDatePicker - YearMode"),
      onPressed: (){
        showDatePicker(
          context: context,
          initialDatePickerMode: DatePickerMode.year, // 日期选择模式，默认为天数选择
          initialEntryMode: DatePickerEntryMode.calendar, // 日历弹框样式
          initialDate: DateTime.now(), // 初始化选中日期
          firstDate: DateTime(2015, 6), // 开始日期
          lastDate: DateTime(2025, 6), // 结束日期
          currentDate: DateTime.now(), // 当前日期
          helpText: "年份选择器", // 左上方提示
          cancelText: "取消", // 取消按钮文案
          confirmText: "确认", // 确认按钮文案
        );
      },
    );
  }

  ElevatedButton _showDatePickerForInput(context) {
    return ElevatedButton(
      child: Text("showDatePicker - InputMode"),
      onPressed: (){
        showDatePicker(
            context: context,
            initialEntryMode: DatePickerEntryMode.input,  // 日历弹框样式
            initialDate: DateTime.now(), // 初始化选中日期
            firstDate: DateTime(2020, 6), // 开始日期
            lastDate: DateTime(2021, 6), // 结束日期
            textDirection: TextDirection.rtl, // 文字方向

            currentDate: DateTime(2020, 10, 20), // 当前日期
            helpText: "helpText", // 左上方提示
            cancelText: "cancelText", // 取消按钮文案
            confirmText: "confirmText", // 确认按钮文案

            errorFormatText: "errorFormatText",  // 格式错误提示
            errorInvalidText: "errorInvalidText",  // 输入不在 first 与 last 之间日期提示

            fieldLabelText: "fieldLabelText",  // 输入框上方提示
            fieldHintText: "fieldHintText",  // 输入框为空时内部提示

            // initialDatePickerMode: DatePickerMode.day, // 日期选择模式，默认为天数选择
            useRootNavigator: true, // 是否为根导航器
            // 设置不可选日期，这里将 2020-10-15，2020-10-16，2020-10-17 三天设置不可选
            selectableDayPredicate: (dayTime){
              if (dayTime == DateTime(2020, 10, 15) || dayTime == DateTime(2020, 10, 16) || dayTime == DateTime(2020, 10, 17)) {
                return false;
              }
              return true;
            }
        );
      },
    );
  }

  ElevatedButton _showDatePickerForTheme(context) {
    return ElevatedButton(
      child: Text("showDatePicker - InputMode"),
      onPressed: (){
        showDatePicker(
          context: context,
          builder: (context, child) {
            return Theme(
              data: ThemeData(
                cardColor: Colors.red,
                brightness: Brightness.dark,
              ),
              child: child,
            );
          },
          initialDatePickerMode: DatePickerMode.year, // 日期选择模式，默认为天数选择
          initialDate: DateTime.now(), // 初始化选中日期
          firstDate: DateTime(2018, 6),  // 开始日期
          lastDate: DateTime(2025, 6),  // 结束日期
          currentDate: DateTime(2020, 10, 20),  // 当前日期
          helpText: "helpText", // 左上方提示
          cancelText: "cancelText",  // 取消按钮文案
          confirmText: "confirmText",  // 确认按钮文案
        );
      },
    );
  }

  ElevatedButton _showTimePicker(context) {
    return ElevatedButton(
      child: Text("showTimePicker - InputMode"),
      onPressed: (){
        showTimePicker(
          context: context,
          initialTime: TimeOfDay(hour: 10, minute: 30),
          initialEntryMode: TimePickerEntryMode.input,
          helpText: "时间选择器",
          cancelText: "取消",
          confirmText: "确定"
        );
      },
    );
  }

  CalendarDatePicker _calendarDatePicker(DatePickerMode mode) {
    return CalendarDatePicker(
      initialCalendarMode: mode, // 日期选择样式
      initialDate: DateTime.now(), // 初始化选中日期~
      currentDate: DateTime.now(), // 当前日期~
      firstDate: DateTime(2010, 9, 10),  // 开始日期
      lastDate: DateTime(2030, 9, 10),  // 结束日期
      
      // 选中日期改变回调函数
      onDateChanged: (dateTime){
        print("选择日期 $dateTime");
      },
      // 月份改变回调函数
      onDisplayedMonthChanged: (dateTime){
        print("选择月份 $dateTime");
      },
      // 筛选日期可不可点回调函数
      selectableDayPredicate: (dayTime) {
        if (dayTime == DateTime(2021, 1, 15)) {
          return false;
        }
        return true;
      }
    );
  }

  CupertinoTimerPicker _cupertinoTimePicker(CupertinoTimerPickerMode mode) {
    return CupertinoTimerPicker(
      mode: mode, // 展示模式，默认为 hms
      initialTimerDuration: Duration(hours: 5, minutes: 10), // 默认选中时间
      minuteInterval: 10, // 分钟间隔
      secondInterval: 10, // 秒间隔
      alignment: Alignment.center, // 对齐方式
      backgroundColor: Colors.amber[200], // 背景颜色
      // 滑动后，每次改变回调函数
      onTimerDurationChanged: (dayTime){
        print("选中时间 $dayTime");
      },
    );
  }

  Container _cupertinoDatePicker(CupertinoDatePickerMode mode) {
    return Container(
      height: 300,
      child: CupertinoDatePicker(
        mode: mode, // 展示模式, 默认为 dateAndTime
        initialDateTime: DateTime(2020, 10, 10), // 默认选中日期
        minimumDate: DateTime(2010, 10, 10), // 最小可选日期
        maximumDate: DateTime(2021, 10, 10), // 最大可选日期
        minuteInterval: 10, // 分钟间隔
        use24hFormat: true, // 是否采用24小时制
        backgroundColor: Colors.greenAccent[200], // 背景色
        onDateTimeChanged: (dayTime) {
          print("选择日期时间 $dayTime");
        },
      ),
    );
  }
}

十八、表单-Form

• 使用步骤
  • 创建表单 Form，并以 GlobalKey 作为唯一性标识
  • 添加带验证逻辑的 TextFormField 到 Form 中
  • 创建按钮以验证和提交表单
• Form (表单容器）
  • key (GlobalKey)
  • child （子组件)
• TextFormField (输入框)
  • 与 TextField 的区别：必须在 Form 内使用 & 带有验证器
  • validator （验证器）

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Form"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: FormDemo()
    );
  }
}

class FormDemo extends StatefulWidget {
  FormDemo({Key key}) : super(key: key);

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

class _FormDemoState extends State<FormDemo> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(20),
      child: Column(
        children: [
          Form(
            key: _formKey,
            child: Column(
              children: [
                TextFormField(
                  decoration: InputDecoration(
                    hintText: '手机号'
                  ),
                  validator: (value) {
                    RegExp reg = new RegExp(r'^\d{11}$');
                    if (!reg.hasMatch(value)) {
                      return '手机号非法111';
                    }
                    return null;
                  }
                )
              ],
            )
          ),
          Row(
            children: [
              Expanded(
                child: ElevatedButton(
                  onPressed: () {
                    if (_formKey.currentState.validate()) {
                      print('提交成功');
                    }
                  }, 
                  child: Text('提交'),
                )
              )
            ],
          )
        ],
      ),
    );
  }
}

十九、表单-Form

• Form （表单容器）
  • 创建表单唯一键：final GlobalKey_formKey = GlobalKey();
  • 验证表单: _formKey.currentState.validate()
  • 提交表单：_formKey.currentState.ve()
  • 重置表单： _formKey.currentState.reset()
• TextFormField (输入框)
  • validator（验证器）
  • obscureText （密码框）
  • onSaved
    • 设定表单字段的值
    • 在表单的方法之后执行

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Form"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: FormDemo()
    );
  }
}

class FormDemo extends StatefulWidget {
  FormDemo({Key key}) : super(key: key);

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

class _FormDemoState extends State<FormDemo> {
  final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
  String _phone;
  String _password;

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(20),
      child: Column(
        children: [
          Form(
            key: _formKey,
            child: Column(
              children: [
                TextFormField(
                  decoration: InputDecoration(
                    hintText: '手机号'
                  ),
                  validator: (value) {
                    RegExp reg = new RegExp(r'^\d{11}$');
                    if (!reg.hasMatch(value)) {
                      return '手机号非法111';
                    }
                    return null;
                  },
                  onSaved: (value) {
                    print('_phone onSaved');
                    _phone = value;
                  },
                ),
                TextFormField(
                  obscureText: true,
                  decoration: InputDecoration(
                    hintText: '密码'
                  ),
                  validator: (value) {
                    return value.length < 6 ? "密码长度不够": null;
                  },
                  onSaved: (value) {
                    print('_password onSaved');
                    _password = value;
                  },
                )
              ],
            )
          ),
          Row(
            children: [
              Expanded(
                child: ElevatedButton(
                  onPressed: () {
                    if (_formKey.currentState.validate()) {
                      print('提交成功');
                      // 提交表单
                      print('_formKey.currentState.save() - Before');
                      _formKey.currentState.save();
                      print('_formKey.currentState.save() - After');
                      print(_phone);
                      print(_password);
                    }
                  }, 
                  child: Text('提交'),
                )
              ),
              SizedBox(
                width: 20,
              ),
              Expanded(
                child: ElevatedButton(
                  onPressed: () {
                    _formKey.currentState.reset();
                  }, 
                  child: Text('重置'),
                )
              )
            ],
          )
        ],
      ),
    );
  }
}

二十、动画

• Why
  • UI 界面设计合理的动画，可以让用户觉得更加流畅、直观，可以极大提高和改善用户体验。
• What (实现原理)
  • 动画就是动起来的画面
  • 视觉暂留：画面经视神经传入大脑后，不会立即消失（会存留一段时间）
  • 帧（Frame）：单个的画面，在学术上叫帧。
  • 每秒中展示的帧数简称fps (Frame per Second)

动画分类

• 补间（Tween）动画
  • 在补间动画中我们定义开始点和结束点、时间线以及定义转换时间和速度曲线。然后由系统计算，从开始点运动到结束点。从而形成动画效果
  • 例如：透明度从 0 到 1，颜色值从 0 到 255
• 拟物动画
  • 拟物动画是对真实世界的行为进行建模，使动画效果类似于现实中的物理效果。
  • 例如：弹簧，阻尼，重力，抛物线等。

动画-Animation

• Animation，是 Flutter 动画库中的一个核心类。它包含动画的值和状态两个属性，定义了动画的一系列监听函数。
  • 监听值：
    • addListener
    • removeListener
  • 监听状态：
    • addStatusListener
    • removeStatusListener

动画状态

• AnimationStatus.dismissed
  • 动画初始状
• AnimationStatus.completed
  • 动画结束状
• AnimationStatus.forward
  • 动画处在从开始到结束的运行状态
• AnimationStatus.reverse
  • 动画处在从结束到开始的运行状态

动画-AnimationController

• AnimationController （动画控制器）
  • 在指定时间内，将组件属性值由初始值演变到终止值。从而形成动画效果。
• AnimationController 参数
  • duration (动画的执行时间)
  • reverseDuration (动画反向执行时间)
  • lowerBound =0.0 (动画最小值)
  • upperBound =1.0 (动画最大值)
  • value（动画初始值，默认是 lowerBound）
  • vsync（TickerProvider 类型的对象，用来创建 Ticker 对象）

动画-AnimationController

• 当创建一个 AnimationController 时，需要传递一个 vsync 参数
  • vsync 的作用是：防止屏幕外动画（动画页面切换到后台时）消耗不必要的资源
  • 通过将 SingleTickerProviderStateMixin 添加到类定义中，可以将 stateful 对象作为vsync 的值。
• AnimationController 具有控制动画的方法：
  • forward()可以正向执行动画
  • reverse()可以反向执行动画
  • dispose()用来释放动画资源（在不使用时需要调用该方法，否则会造成资源泄露）
  • stop（）用来停止动画运行

动画-Tween

• 简介
  • AnimationController 动画生成值的默认区间是 0.0 到 1.0，如果希望使用不同的区间,或不同的数据类型,需要使用Tween (补间动画)
  • Tween 的唯一职责就是定义从输入范围到输出范围的映射。
  • 例如：颜色区间是 0到 255
• Tween
  • Tween(begin： 起始值，end： 终止值)；
  • ColorTween(begin: Colors.withe, end: Colors.black);

动画-CurvedAnimation

• 简介
  • 动画执行的速度有多种（匀速、先快后慢或先慢后快）这里的速度称为动画曲线CurvedAnimation 的目的是为 AnimationController 添加动画曲线
• 组件
  • CurvedAnimation(parent: controller, curve: Curves.easeln)
  • parent (动画控制器对象)
  • curve(正向执行的动画曲线）
  • reverseCurve （反向执行的动画曲线）
• Curves
  • 动画曲线: https://api.flutter.dev/flutter/animation/Curves-class.html

动画-步骤

• 创建动画控制器
  • controller = AnimationController(duration, vsync)
• 创建动画
  • 动画曲线(CurvedAnimation)
  • 补间动画（Tween）
• 监听动画
  • addListener() // 监听动画生成值addStatusListener() //监听动画状态执行动画
  • controller.forward()// 正向执行
  • controller.reverse()// 反向执行

import 'package:flutter/material.dart';

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Animation"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: AnimationDemo()
    );
  }
}

class AnimationDemo extends StatefulWidget {
  AnimationDemo({Key key}) : super(key: key);

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

class _AnimationDemoState extends State<AnimationDemo> with SingleTickerProviderStateMixin {
  AnimationController controller;
  Animation animation;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    // 1.创建 AnimationController
    controller = AnimationController(
      duration: Duration(milliseconds: 400),
      vsync: this
    );

    // 2.1 声明动画曲线
    animation = CurvedAnimation(parent: controller, curve: Curves.bounceIn);

    // 2.2 设置动画值的范围
    animation = Tween(begin: 50.0, end: 400.0).animate(controller);

    // 3. 监听动画
    animation.addListener(() {
      print(animation.value);
      setState(() {
        
      });
    });

    // 4. 执行动画
    // controller.forward();
  }

  @override
  Widget build(BuildContext context) {
    return Center(
       child: Column(
         children: [
           ElevatedButton(
             onPressed: () {
               controller.forward();
             }, 
             child: Text('放大')
           ),
           ElevatedButton(
             onPressed: () {
               controller.reverse();
             }, 
             child: Text('缩小')
           ),
           ElevatedButton(
             onPressed: () {
               animation.addStatusListener((status) {
                 if (status == AnimationStatus.completed) {
                   // 反向执行动画
                   controller.reverse();
                 } else if (status == AnimationStatus.dismissed) {
                   // 正向执行动画
                   controller.forward();
                 }
               });
               controller.forward();
             }, 
             child: Text('重复')
           ),
           ElevatedButton(
             onPressed: () {
               controller.stop();
             }, 
             child: Text('停止')
           ),
           Icon(
             Icons.favorite,
             color: Colors.red,
             size: animation.value
           ),
           Opacity(
             opacity: controller.value,
             child: Text('Hello World')
           )
         ],
       ),
    );
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    controller.dispose();
  }
}

交织动画

• What?
  • 交织动画是由多个单一动画叠加而成复杂动画
  • 例如：组件变化可能涉及高度、宽度、颜色、透明度、位置等等
  • 需要给每个动画设置时间间隔（Interval）
• Transform (对组件进行矩阵变换)
  • 平移：Transform.translate()
  • 旋转: Transform.rotate
  • 缩放：Transform.scale()

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Stagger Animation"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: AnimationDemo()
    );
  }
}

class AnimationDemo extends StatefulWidget {
  AnimationDemo({Key key}) : super(key: key);

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

class _AnimationDemoState extends State<AnimationDemo> with SingleTickerProviderStateMixin {
  AnimationController controller;
  Animation animation;
  Animation sizeAnimation;
  Animation colorAnimation;
  Animation rotationAnimation;

  @override
  void initState() {
    // TODO: implement initState
    super.initState();

    // 1. 创建 AnimationController
    controller = AnimationController(
      duration: Duration(seconds: 3),
      vsync: this,
    );

    // 2. 创建动画
    animation = CurvedAnimation(
      parent: controller, 
      curve: Interval(0.0, 0.5)
    )..addListener(() {
      setState(() {
        
      });
      });

    // 3. 让动画反复运行
    animation.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        // 反向执行动画
        controller.reverse();
      } else if (status == AnimationStatus.dismissed) {
        // 正向执行动画
        controller.forward();
      }
    });

    // 4. 设置其他动画
    sizeAnimation = Tween(begin: 0.0, end: 200.0).animate(animation);
    colorAnimation = ColorTween(begin: Colors.yellow, end: Colors.red)
      .animate(CurvedAnimation(
        parent: controller, 
        curve: Interval(0.5, 0.8, curve: Curves.bounceIn)
      ))
      ..addListener(() { 
        setState(() {
          
        });
      });

    rotationAnimation = Tween(begin: 0.0, end: 2*pi).animate(
      CurvedAnimation(
        parent: controller, 
        curve: Interval(0.8, 1.0, curve: Curves.easeIn)
      )
    );
  }

  @override
  Widget build(BuildContext context) {
    return Center(
       child: Column(
         children: [
           ElevatedButton(
             onPressed: () {
              //  animation.addStatusListener((status) {
              //    if (status == AnimationStatus.completed) {
              //      // 反向执行动画
              //      controller.reverse();
              //    } else if (status == AnimationStatus.dismissed) {
              //      // 正向执行动画
              //      controller.forward();
              //    }
              //  });
               controller.forward();
             }, 
             child: Text('重复')
           ),
           ElevatedButton(
             onPressed: () {
               controller.stop();
             }, 
             child: Text('停止')
           ),
Opacity(
  opacity: controller.value,
  child: Transform.rotate(
    angle: rotationAnimation.value,
    child: Container(
      width: sizeAnimation.value,
      height: sizeAnimation.value,
      color: colorAnimation.value
    )
  )
)
         ],
       ),
    );
  }

  @override
  void dispose() {
    // TODO: implement dispose
    super.dispose();
    controller.dispose();
  }
}

二十一、Hero 动画

• Hero 动画用来实现跨页面的动画效果
  • 在不同页面中，声明一个共享组件（Hero)
  • 由于共享组件在不同页面中的位置、外观等不同，路由切换时，形成动画效果
• 如何实现
  • 在页面 A 中定义起始 Hero 组件（source hero），声明 tag
  • 在页面 B 中定义目标 Hero 组件（destination hero），绑定相同的 tag
  • 页面跳转时，通过 Navigator，传递 tag
• Hero 组件
  • tag（路由切换时，共享组件的标记）
  • child (声明子组件）

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

class Home extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Hero Animation"),
        leading: Icon(Icons.menu),
        actions: [
          Icon(Icons.settings)
        ],
        elevation: 0.0,
        centerTitle: true,
      ),
      body: HeroAnimation()
    );
  }
}

class HeroAnimation extends StatelessWidget {
  const HeroAnimation({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.symmetric(vertical: 20),
      child: GridView.extent(
        maxCrossAxisExtent: 200.0,
        mainAxisSpacing: 20,
        children: List.generate(20, (index) {
          String imageURL = "https://picsum.photos/id/$index/300/400";
          return GestureDetector(
            onTap: () {
              Navigator.push(context, MaterialPageRoute(builder: (BuildContext ctx) {
                return ImageDetail(imageURL);
              }));
            },
            child: Hero(
              tag: imageURL, 
              child: Image.network(imageURL)
            )
          );
        })
      ),
    );
  }
}

import 'package:flutter/material.dart';

class ImageDetail extends StatelessWidget {
  final String imageURL;
  ImageDetail(this.imageURL);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.black,
      body: Center(
        child: GestureDetector(
          onTap: () {
            // 调回去
            Navigator.pop(context);
          },
          child: Hero(
            tag: imageURL, 
            child: Image.network(
              imageURL,
              width: double.infinity,
              fit: BoxFit.cover
            )
          )
        )
      )
    );
  }
}

二十二、多语言（国际化）

• 国际化(internationalization 简称 i18n)
  • 终端(手机)系统语言切换时, Flutter应用的跟随切换,
• 内容
  • 组件（Widget）国际化
    • 例如：日历，弹窗等常用组件的国际化
  • 文本国际化（包括文本的顺序）
    • 自定义文本的国际化

多语言（国际化）-组件

• 在 pubspec.yaml 中引入 flutter_localizations
  • 安装包： flutter pub get (VS Code 中保存自动安装)
• 设置 MaterialApp
  • import ‘package:flutter_localizations/flutter_localizations.dart’;
  • localizationsDelegates（指定哪些组件需要进行国际化）
  • supportedlocales（指定要支持哪些语言）

多语言(国际化) -文本

• 创建本地化类
  • CustomLocalizations
• 创建本地化类的代理
  • CustomLocalizationsDelegate extends LocalizationsDelegate
    • isSupported（当前本地化，是否在有效的语言范围内
    • shouldReload（本地化重新构建时，是否调用 load 方法，加载本地化资源）
    • load（语言发生变更时，加载对应的本地化资源）
• 使用本地化类
  • CustomLocalizations.delegate
    
    
    多语言（国际化）- 文本- 加载语言包
• 检测当前语言
  • localeResolutionCallback
    • locale. languageCode（语言代码，例如：en、zh）
    • locale.countryCode（国家代码，例如：US，CN）
      
• 设置语言包
  • 创建语言文件
  • 在 pubspec.yaml 中配置语言资源
• 异步加载语言包
  • 在 CustomLocalizations 中，添加 loadJSON(） 方法
  • 在 CustomLocalizationsDelegate 中，调用 CustomLocalizations 的 loadJSON（） 方法

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'dart:convert';

class CustomLocalizations {
  final Locale locale;

  CustomLocalizations(this.locale);

  // static Map> _localizedValues = {
    // "en": {
    //   "title": "Home",
    //   "greet": "Hello",
    // },
  //   "zh": {
  //     "title": "首页",
  //     "greet": "你好",
  //   },
  // };

  Map<String, String> _localizedValues;

  Future<bool> loadJSON() async {
    String jsonString = await rootBundle.loadString('lang/${locale.languageCode}.json');
    Map<String, dynamic> jsonMap = json.decode(jsonString);

    _localizedValues = jsonMap.map((key, value) {
      return MapEntry(key, value.toString());
    });

    return true;
  }

  String t(String key) {
    // _localizedValues['zh']['title']
    // return _localizedValues[locale.languageCode][key];
    return _localizedValues[key];
  }

  static CustomLocalizations of(BuildContext context) {
    return Localizations.of(context, CustomLocalizations);
  }

  static CustomLocalizationsDelegate delegate = CustomLocalizationsDelegate();
}

class CustomLocalizationsDelegate extends LocalizationsDelegate<CustomLocalizations> {
  @override
  bool isSupported(Locale locale) {
    return ["en", "zh"].contains(locale.languageCode);
  }

  @override
  Future<CustomLocalizations> load(Locale locale) async {
    // return SynchronousFuture(CustomLocalizations(locale));
    CustomLocalizations localizations = CustomLocalizations(locale);
    await localizations.loadJSON();
    return localizations;
  }

  @override
  bool shouldReload(covariant LocalizationsDelegate<CustomLocalizations> old) {
    return false;
  }
}

二十三、多主题

• 主题（UI风格、样式、皮肤）
• 主题风格可通过 theme 来定义，从而实现整个 App 风格的统一
• 一旦设置了主题,那么应用程序中的某些 Widget, 就会直接使用主题的样式
  组件
  ThemeData
  Brightness (Brightness.light | Brightness.dark)
  primaryColor | accentColor
  buttonTheme | cardTheme | iconTheme | textTheme
  Theme (声明局部主题)
  Theme.of(context) 获取上下文中的主题信息

多主题-适配终端

• 声明不同的主题
  • CustomTheme
• 使用主题import ‘CustomTheme.dart’;
  • theme: CustomTheme.lightTheme,
  • darkTheme: CustomTheme.darkTheme,
  • theme: ThemeData.light(),
  • darkTheme: ThemeData.dark(),
• 查看效果
  • 模拟器中切换主题，Flutter 应用中查看效果

import 'package:flutter/material.dart';

class CustomTheme {
  // 公共样式
  static const double _CardBorderWidth = 20;
  static const double _CardElevation = 20;

  // 高亮主题
  static final ThemeData lightTheme = ThemeData(
    primaryColor: Colors.red,
    cardTheme: CardTheme(
      color: Colors.red[100],
      shape: Border.all(width: _CardBorderWidth, color: Colors.red),
      elevation: _CardElevation,
    )
  );

  // 黑暗主题
  static final ThemeData darkTheme = ThemeData(
    primaryColor: Colors.grey,
    cardTheme: CardTheme(
      color: Colors.grey[100],
      shape: Border.all(width: _CardBorderWidth, color: Colors.black45),
      elevation: _CardElevation,
    )
  );
}