(摘) 高级布局之栈索引IndexedStack

IndexedStack 继承自Stack，用于显示第index个child，而其他child则是不可见的。所以IndexedStack的尺寸永远是跟最大的子控件尺寸一致。与Stack相比，只是多了index的设置。

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 MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _pageIndex = 0;

  void onClick(int index) {
    setState(() {
      _pageIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Column(
        children: [
          Expanded(
            child: IndexedStack(
              index: _pageIndex,
              children: [
                Container(color: Colors.red),
                Container(color: Colors.grey),
                Container(color: Colors.yellow),
              ],
            ),
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              TextButton(
                  child: const Icon(Icons.home), onPressed: () => onClick(0)),
              TextButton(
                  child: const Icon(Icons.abc), onPressed: () => onClick(1)),
              TextButton(
                  child: const Icon(Icons.search), onPressed: () => onClick(2)),
            ],
          ),
        ],
      ),
    );
  }
}

稍作修改，设置应用主题色和统一字体

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

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

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primaryColor: Colors.blue,
        textTheme: const TextTheme(
          headline1: TextStyle(
              fontSize: 36.0, fontWeight: FontWeight.bold, color: Colors.white),
          headline2: TextStyle(
              fontSize: 32.0, fontWeight: FontWeight.w400, color: Colors.white),
          headline3: TextStyle(
              fontSize: 28.0, fontWeight: FontWeight.w400, color: Colors.white),
          headline4: TextStyle(
              fontSize: 24.0, fontWeight: FontWeight.w400, color: Colors.white),
          headline6: TextStyle(
              fontSize: 14.0, fontWeight: FontWeight.w200, color: Colors.white),
          bodyText1: TextStyle(
            fontSize: 20.0,
            fontWeight: FontWeight.w200,
          ),
        ),
        colorScheme:
            ColorScheme.fromSwatch().copyWith(secondary: Colors.blue[600]),
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _pageIndex = 0;

  void onClick(int index) {
    setState(() {
      _pageIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(
          widget.title,
          style: Theme.of(context).textTheme.headline4,
        ),
        systemOverlayStyle: SystemUiOverlayStyle.light,
      ),
      body: Column(
        children: [
          Expanded(
            child: IndexedStack(
              index: _pageIndex,
              alignment: AlignmentDirectional.topStart,
              children: [
                Container(color: Colors.red),
                Container(color: Colors.grey),
                Container(color: Colors.yellow),
              ],
            ),
          ),
          Row(
            mainAxisAlignment: MainAxisAlignment.center,
            textDirection: TextDirection.rtl,
            children: [
              TextButton(
                  child: const Icon(Icons.home), onPressed: () => onClick(0)),
              TextButton(
                  child: const Icon(Icons.abc), onPressed: () => onClick(1)),
              TextButton(
                  child: const Icon(Icons.search), onPressed: () => onClick(2)),
            ],
          ),
        ],
      ),
    );
  }
}