Displaying notification badge on BottomNavigationBar's Icon

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

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

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

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
      bottomNavigationBar: BottomNavigationBar(
        type: BottomNavigationBarType.fixed,
        items: <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Stack(
              children: <Widget>[
                Icon(Icons.notifications),
                Positioned(
                  right: 0,
                  child: Container(
                    padding: EdgeInsets.all(1),
                    decoration: BoxDecoration(
                      color: Colors.red,
                      borderRadius: BorderRadius.circular(6),
                    ),
                    constraints: BoxConstraints(
                      minWidth: 12,
                      minHeight: 12,
                    ),
                    child: Text(
                      '1',
                      style: TextStyle(
                        color: Colors.white,
                        fontSize: 8,
                      ),
                      textAlign: TextAlign.center,
                    ),
                  ),
                )
              ],
            ),
            title: Text('Notifications'),
          ),
          BottomNavigationBarItem(
            icon: Stack(
              children: <Widget>[
                Icon(Icons.notifications),
                Positioned(
                  right: 0,
                  child: Container(
                    padding: EdgeInsets.all(1),
                    decoration: BoxDecoration(
                      color: Colors.red,
                      borderRadius: BorderRadius.circular(6),
                    ),
                    constraints: BoxConstraints(
                      minWidth: 12,
                      minHeight: 12,
                    ),
                    child: Text(
                      '10',
                      style: TextStyle(
                        color: Colors.white,
                        fontSize: 8,
                      ),
                      textAlign: TextAlign.center,
                    ),
                  ),
                )
              ],
            ),
            title: Text('Notifications'),
          ),
          BottomNavigationBarItem(
            icon: Stack(
              children: <Widget>[
                Icon(Icons.notifications),
                Positioned(
                  right: 0,
                  child: Container(
                    padding: EdgeInsets.all(1),
                    decoration: BoxDecoration(
                      color: Colors.red,
                      borderRadius: BorderRadius.circular(6),
                    ),
                    constraints: BoxConstraints(
                      minWidth: 12,
                      minHeight: 12,
                    ),
                    child: Text(
                      '100',
                      style: TextStyle(
                        color: Colors.white,
                        fontSize: 8,
                      ),
                      textAlign: TextAlign.center,
                    ),
                  ),
                )
              ],
            ),
            title: Text('Notifications'),
          ),
        ],
      ),
    );
  }
}