[flutter3]NavigationBarの基本的な使い方（サンプルコード付き）

Index

NavigationBarとは？

flutter2ではBottomNavigationBarとして実装されていましたが、flutter3からはNavigationBarに変わりました。

と言ってもほぼ一緒なのですが、実装方法がちょっと異なります。

サンプルコードと成果物

以下のサンプルコード（４ファイル）をコピペして使うと動画と同じ挙動をするアプリが作れます。

gitにも同じものを上げているので、適宜参照ください。

https://github.com/jostar0024/NavigationBarSample

main.dart

import 'package:flutter/material.dart';
import 'package:waterdiary/diary_view.dart';
import 'package:waterdiary/home_view.dart';
import 'package:waterdiary/settings_view.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 _selectedIndex = 0;

  final List<Widget> _widgetList = <Widget>[
    const HomeView(),
    const DiaryView(),
    const SettingView(),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      bottomNavigationBar: NavigationBar(
        destinations: const [
          NavigationDestination(icon: Icon(Icons.home), label: 'home'),
          NavigationDestination(icon: Icon(Icons.menu_book), label: 'diary'),
          NavigationDestination(icon: Icon(Icons.settings), label: 'settings'),
        ],
        onDestinationSelected: (index) => setState(() {
          _selectedIndex = index;
        }),
        selectedIndex: _selectedIndex,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[_widgetList.elementAt(_selectedIndex)],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';

import 'package:waterdiary/diary_view.dart';

import 'package:waterdiary/home_view.dart';

import 'package:waterdiary/settings_view.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 _selectedIndex = 0;

final List<Widget> _widgetList = <Widget>[

const HomeView(),

const DiaryView(),

const SettingView(),

];

@override

Widget build(BuildContext context) {

return Scaffold(

appBar: AppBar(

title: Text(widget.title),

bottomNavigationBar: NavigationBar(

destinations: const [

NavigationDestination(icon: Icon(Icons.home), label: 'home'),

NavigationDestination(icon: Icon(Icons.menu_book), label: 'diary'),

NavigationDestination(icon: Icon(Icons.settings), label: 'settings'),

onDestinationSelected: (index) => setState(() {

_selectedIndex = index;

}),

selectedIndex: _selectedIndex,

body: Center(

child: Column(

mainAxisAlignment: MainAxisAlignment.center,

children: <Widget>[_widgetList.elementAt(_selectedIndex)],

);

}

home_view.dart

import 'package:flutter/material.dart';

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

  @override
  State<HomeView> createState() => _HomeViewState();
}

class _HomeViewState extends State<HomeView> {
  @override
  Widget build(BuildContext context) {
    return const Text('Home');
  }
}

import 'package:flutter/material.dart';

class HomeView extends StatefulWidget {

const HomeView({Key? key}) : super(key: key);

@override

State<HomeView> createState() => _HomeViewState();

}

class _HomeViewState extends State<HomeView> {

@override

Widget build(BuildContext context) {

return const Text('Home');

}

diary_view.dart

import 'package:flutter/material.dart';

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

  @override
  State<DiaryView> createState() => _DiaryViewState();
}

class _DiaryViewState extends State<DiaryView> {
  @override
  Widget build(BuildContext context) {
    return const Text('Diary');
  }
}

import 'package:flutter/material.dart';

class DiaryView extends StatefulWidget {

const DiaryView({Key? key}) : super(key: key);

@override

State<DiaryView> createState() => _DiaryViewState();

}

class _DiaryViewState extends State<DiaryView> {

@override

Widget build(BuildContext context) {

return const Text('Diary');

}

settings_view.dart

import 'package:flutter/material.dart';

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

  @override
  State<SettingView> createState() => _SettingViewState();
}

class _SettingViewState extends State<SettingView> {
  @override
  Widget build(BuildContext context) {
    return const Text('Setting');
  }
}

import 'package:flutter/material.dart';

class SettingView extends StatefulWidget {

const SettingView({Key? key}) : super(key: key);

@override

State<SettingView> createState() => _SettingViewState();

}

class _SettingViewState extends State<SettingView> {

@override

Widget build(BuildContext context) {

return const Text('Setting');

}

成果物

ポイント

ポイントをコメントで追記しましたので、ご確認ください。

destinationsの数は３〜５個が適切だと公式リファレンスに書いてあります。

Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
　　　　　//NavigationBarの指定
      bottomNavigationBar: NavigationBar(　
        //アイコンとテキストのセット
        destinations: const [
          NavigationDestination(icon: Icon(Icons.home), label: 'home'),
          NavigationDestination(icon: Icon(Icons.menu_book), label: 'diary'),
          NavigationDestination(icon: Icon(Icons.settings), label: 'settings'),
        ],
        //アイコンが押されたときに選択せれているアイコンを変更する
        onDestinationSelected: (index) => setState(() {
          _selectedIndex = index;
        }),
        //選択されているアイコンを設定
        selectedIndex: _selectedIndex,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[_widgetList.elementAt(_selectedIndex)],//表示する画面を指定する
        ),
      ),
    );