前言

本來想把之前自己的ReactNative的Demo項(xiàng)目拿來變成Flutter版本，但是這幾年一直搞Native開發(fā)回過頭去看RN的項(xiàng)目好多都不明白了，真是開發(fā)者的噩夢(mèng)，接觸好多東西不使用的話漸漸地都模糊了，所以還是得把有的東西重點(diǎn)記下來非区，就相當(dāng)于是自己的筆記一樣沒事翻著看看，這次Flutter就選擇豆瓣去嘗試下盹廷，畢竟豆瓣也有開放的API供開發(fā)者使用

底部導(dǎo)航

微信圖片_20220529161305.jpg

首頁 書影音 小組 市集 我

這部分選擇使用BottomNavigationBar 去做底部導(dǎo)航欄的實(shí)現(xiàn)

搭建項(xiàng)目

創(chuàng)建一個(gè)新的Flutter項(xiàng)目

將HomePage相關(guān)抽離出來到另一個(gè)Dart文件中征绸，并更改部分命名為MainPage

使用Route管理頁面切換，默認(rèn)進(jìn)入Main頁面

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實(shí)現(xiàn)底部導(dǎo)航UI俄占，并為底部導(dǎo)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: '首頁'),
          BottomNavigationBarItem(icon: Icon(Icons.book), label: '書影音'),
          BottomNavigationBarItem(icon: Icon(Icons.group), label: '小組'),
          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)
        },
      ),
    );
  }
}

這里默認(rèn)使用了有狀態(tài)可變的StatefulWidget是因?yàn)槲覀兊捻撁媸强勺兊墓艿。谖覀冞x中其他底部功能時(shí)頁面是需要刷新的

onTap函數(shù)調(diào)用之后，我們更改了屬性currentIndex 缸榄，同時(shí)調(diào)用了

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

然后界面就會(huì)刷新渤弛，build函數(shù)會(huì)重新去渲染已得到更新的頁面，細(xì)節(jié)后面我們可以一起看看setState函數(shù)的實(shí)現(xiàn)

效果

微信圖片_20220529173942.jpg

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