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Saturday, August 13, 2022

Flutter: BottomNavigationBar example

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In general, a bottom navigation bar displays two to five tabs at the bottom of a screen of a mobile or web app. Each tab contains an icon and an optional text label.

In Flutter, you can easily implement a bottom tab bar and its tabs by using the built-in widgets named BottomNavigationBar and BottomNavigationBarItem, respectively.Advertisements

Example

App Preview

To demonstrate how to work with BottomNavigationBar, we’ll build a tiny Flutter app that contains 2 screens (ScreenA and ScreenB). To navigate between them, you can use the bottom tab bar. Here’s how it works at the end:

Writing Code

1. Create a new Flutter app:

flutter create my_app 

2. In the lib directory, create 2 new files: screen_a.dart and screen_b.dart. Here’s the file structure in the lib folder:

.
??? main.dart
??? screen_a.dart
??? screen_b.dart

Advertisements3. Add this to screen_a.dart:

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

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

  @override
  Widget build(BuildContext context) {
    return const Center(
      child: Text(
        'Screen A',
        style: TextStyle(fontSize: 30),
      ),
    );
  }
}

4. Add this to screen_b.dart:

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

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

  @override
  Widget build(BuildContext context) {
    return const Center(
      child: Text(
        'Screen B',
        style: TextStyle(fontSize: 30),
      ),
    );
  }
}

5. Remove all the default code in main.dart and add the following:

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

import './screen_a.dart';
import './screen_b.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(
      // Hide the debug banner
      debugShowCheckedModeBanner: false,
      title: 'Kindacode.com',
      home: MyHomePage(),
    );
  }
}

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

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _selectedScreenIndex = 0;
  final List _screens = [
    {"screen": const ScreenA(), "title": "Screen A Title"},
    {"screen": const ScreenB(), "title": "Screen B Title"}
  ];

  void _selectScreen(int index) {
    setState(() {
      _selectedScreenIndex = index;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(_screens[_selectedScreenIndex]["title"]),
      ),
      body: _screens[_selectedScreenIndex]["screen"],
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _selectedScreenIndex,
        onTap: _selectScreen,
        items: const [
          BottomNavigationBarItem(icon: Icon(Icons.home), label: 'Screen A'),
          BottomNavigationBarItem(icon: Icon(Icons.settings), label: "Screen B")
        ],
      ),
    );
  }
}
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6. Launch an iOS simulator or an Android emulator and run:

flutter run

Constructors

BottomNavigationBar:

BottomNavigationBar({
  Key? key, 
  required List<BottomNavigationBarItem> items, 
  ValueChanged<int>? onTap, 
  int currentIndex = 0, 
  double? elevation, 
  BottomNavigationBarType? type, 
  Color? fixedColor, 
  Color? backgroundColor, 
  double iconSize = 24.0, 
  Color? selectedItemColor, 
  Color? unselectedItemColor, 
  IconThemeData? selectedIconTheme, 
  IconThemeData? unselectedIconTheme, 
  double selectedFontSize = 14.0, 
  double unselectedFontSize = 12.0, 
  TextStyle? selectedLabelStyle, 
  TextStyle? unselectedLabelStyle, 
  bool? showSelectedLabels, 
  bool? showUnselectedLabels, 
  MouseCursor? mouseCursor, 
  bool? enableFeedback, 
  BottomNavigationBarLandscapeLayout? landscapeLayout
})

BottomNavigationBarItem:

BottomNavigationBarItem({
  required Widget icon, 
  String? label, 
  Widget? activeIcon, 
  Color? backgroundColor, 
  String? tooltip
})

References

Conclusion

We’ve examined an end-to-end example of implementing a simple material bottom tab bar. If you’d like to explore more new and interesting things about Flutter, take a look at the following articles:

You can also check out our Flutter category page or Dart category page for the latest tutorials and examples.

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