前言

本来想把之前自己的ReactNative的Demo项目拿来变成Flutter版本，但是这几年一直搞Native开发回过头去看RN的项目好多都不明白了，真是开发者的噩梦，接触好多东西不使用的话渐渐地都模糊了，所以还是得把有的东西重点记下来，就相当于是自己的笔记一样没事翻着看看，这次Flutter就选择豆瓣去尝试下，毕竟豆瓣也有开放的API供开发者使用

底部导航

首页 书影音 小组 市集 我

这部分选择使用BottomNavigationBar 去做底部导航栏的实现

搭建项目

创建一个新的Flutter项目

将HomePage相关抽离出来到另一个Dart文件中，并更改部分命名为MainPage

使用Route管理页面切换，默认进入Main页面

class MyApp extends StatelessWidget {  // This widget is the root of your application.  @override  Widget build(BuildContext context) {    return MaterialApp(      title: 'Flutter Demo',      theme: ThemeData(        // This is the theme of your application.        //        // Try running your application with "flutter run". You'll see the        // application has a blue toolbar. Then, without quitting the app, try        // changing the primarySwatch below to Colors.green and then invoke        // "hot reload" (press "r" in the console where you ran "flutter run",        // or simply save your changes to "hot reload" in a Flutter IDE).        // Notice that the counter didn't reset back to zero; the application        // is not restarted.        primarySwatch: Colors.green,      ),      routes: {"/main": (BuildContext context) => MainPage(title: "Main")},      initialRoute: "/main",    );  }}

使用BottomNavigationBar实现底部导航UI，并为底部导航添加事件

class MainPage extends StatefulWidget {  MainPage({Key? key, required this.title}) : super(key: key);  // This widget is the home page of your application. It is stateful, meaning  // that it has a State object (defined below) that contains fields that affect  // how it looks.  // This class is the configuration for the state. It holds the values (in this  // case the title) provided by the parent (in this case the App widget) and  // used by the build method of the State. Fields in a Widget subclass are  // always marked "final".  final String title;  @override  _MainPageState createState() => _MainPageState();}class _MainPageState extends State {  int currentIndex = 0;  void onNavigationChanged(int index) {    setState(() {      currentIndex = index;    });  }  @override  Widget build(BuildContext context) {    // This method is rerun every time setState is called, for instance as done    // by the _incrementCounter method above.    //    // The Flutter framework has been optimized to make rerunning build methods    // fast, so that you can just rebuild anything that needs updating rather    // than having to individually change instances of widgets.    print('build');    return Scaffold(      appBar: AppBar(        // Here we take the value from the MyHomePage object that was created by        // the App.build method, and use it to set our appbar title.        title: Text(widget.title),      ),      body: Center(),      bottomNavigationBar: BottomNavigationBar(        items: const [          BottomNavigationBarItem(icon: Icon(Icons.home), label: '首页'),          BottomNavigationBarItem(icon: Icon(Icons.book), label: '书影音'),          BottomNavigationBarItem(icon: Icon(Icons.group), label: '小组'),          BottomNavigationBarItem(icon: Icon(Icons.store), label: '市集'),          BottomNavigationBarItem(icon: Icon(Icons.person), label: '我')        ],        currentIndex: currentIndex,        unselectedItemColor: Colors.grey,        selectedItemColor: Colors.green,        type: BottomNavigationBarType.fixed,        onTap: (index)=>{          onNavigationChanged(index)        },      ),    );  }}

这里默认使用了有状态可变的StatefulWidget是因为我们的页面是可变的，在我们选中其他底部功能时页面是需要刷新的

onTap函数调用之后，我们更改了属性currentIndex ，同时调用了

   setState(() {      currentIndex = index;    });

然后界面就会刷新，build函数会重新去渲染已得到更新的页面，细节后面我们可以一起看看setState函数的实现

效果

欢迎关注Mike的简书

Android 知识整理