在 Flutter 中更改 body 属性

Question

我有一个非常简单的BottomNavigationBar。我想要完成的是，当我转到另一个选项卡时，body 属性的内容会发生变化，即每个选项卡都有自己的小部件要显示。因此，当索引更改时，我尝试更改 body 属性，但我无法弄清楚如何做到这一点。

主要代码如下：

class _MyHomeState extends State<MyHome> {
  HomeBody obj; //A class that returns a widget according to the index

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: obj.selectHomeBody(),
      bottomNavigationBar: MyBotNavBar(),
    );
  }
}

我的底部导航栏小部件，

class _MyBotNavBarState extends State<MyBotNavBar> {
  int _curIdx = 0;

  @override
  Widget build(BuildContext context) {
    return BottomNavigationBar(
      items: getBotNavListItems(),
      currentIndex: curIdx,
      onTap: (int index) {
        setState(() {
          _curIdx = index;
        });
      },
    );
  }
}

下面的类应该根据索引返回一个小部件，

class HomeBody {
  
  final int _idx = _MyBotNavBarState().curIdx;

  Widget selectHomeBody() {

    Widget widget; //the widget that will be returned
    
   //There might be more cases
    switch (_idx) {
      case 0:
        {
          widget = getHome();
          break;
        }

      
      default:
        {
          widget = getSchool();
          break;
        }
    }
    return widget;
  }

  //defining those widgets
  Widget getHome() {
    return Center(
      child: Text("$_idx Home"),
    );
  }

  Widget getBusiness() {
    return Center(
      child: Text("$_idx Business"),
    );
  }
}

Answer 1

如果我当时就理解了你的问题。
您应该先参考 Flutter 文档，这是文档本身的演示。

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

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

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: MyStatefulWidget(),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State<MyStatefulWidget> createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  int _selectedIndex = 0;
  static const List<Widget> _widgetOptions = <Widget>[
    Text('Page1'),
    Text('Page2'),
    Text('Page3'),
  ];

  void _onItemTapped(int index) {
    setState(() {
      _selectedIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('BottomNavigationBar Sample'),
      ),
      body: Center(
        child: _widgetOptions.elementAt(_selectedIndex),
      ),
      bottomNavigationBar: BottomNavigationBar(
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Page1',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.business),
            label: 'Page2',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.school),
            label: 'Page3',
          ),
        ],
        currentIndex: _selectedIndex,
        selectedItemColor: Colors.amber[800],
        onTap: _onItemTapped,
      ),
    );
  }
}

所以他们在这里创建了一个您想要显示的小部件列表_widgetOptions，然后他们更改了_selectedIndex 的值并重新渲染了 UI 以进行必要的更改。

这里是那篇文章的链接BottomNavigationBar