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

微信图片_20220529161305.jpg

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<MainPage> {
  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>[
          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

微信图片_20220529173942.jpg

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Android 知识整理