试试这个：
import 'dart:async';
import 'package:flutter/material.dart';
import 'badge_icon.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatefulWidget {
@override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
StreamController<int> _countController = StreamController<int>();
int _currentIndex = 0;
int _tabBarCount = 0;
List<Widget> _pages;
Widget _tabBar() {
return BottomNavigationBar(
items: [
const BottomNavigationBarItem(
icon: Icon(Icons.home, size: 25),
title: const Text("Increment"),
),
BottomNavigationBarItem(
icon: StreamBuilder(
initialData: _tabBarCount,
stream: _countController.stream,
builder: (_, snapshot) => BadgeIcon(
icon: Icon(Icons.chat, size: 25),
badgeCount: snapshot.data,
),
),
title: const Text("Decrement"),
),
],
currentIndex: _currentIndex,
onTap: (index) => setState(() => _currentIndex = index),
);
}
@override
void initState() {
_pages = [
Container(
child: Center(
child: FlatButton(
child: Text('Increment'),
onPressed: () {
_tabBarCount = _tabBarCount + 1;
_countController.sink.add(_tabBarCount);
},
),
),
),
Container(
child: Center(
child: FlatButton(
child: Text('Decrement'),
onPressed: () {
_tabBarCount = _tabBarCount - 1;
_countController.sink.add(_tabBarCount);
},
),
),
),
];
super.initState();
}
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Tab Bar Icon Badge'),
),
body: _pages[_currentIndex],
bottomNavigationBar: _tabBar(),
);
}
@override
void dispose() {
_countController.close();
super.dispose();
}
}
徽章图标小部件：
import 'package:flutter/material.dart';
class BadgeIcon extends StatelessWidget {
BadgeIcon(
{this.icon,
this.badgeCount = 0,
this.showIfZero = false,
this.badgeColor = Colors.red,
TextStyle badgeTextStyle})
: this.badgeTextStyle = badgeTextStyle ??
TextStyle(
color: Colors.white,
fontSize: 8,
);
final Widget icon;
final int badgeCount;
final bool showIfZero;
final Color badgeColor;
final TextStyle badgeTextStyle;
@override
Widget build(BuildContext context) {
return new Stack(children: <Widget>[
icon,
if (badgeCount > 0 || showIfZero) badge(badgeCount),
]);
}
Widget badge(int count) => Positioned(
right: 0,
top: 0,
child: new Container(
padding: EdgeInsets.all(1),
decoration: new BoxDecoration(
color: badgeColor,
borderRadius: BorderRadius.circular(8.5),
),
constraints: BoxConstraints(
minWidth: 15,
minHeight: 15,
),
child: Text(
count.toString(),
style: new TextStyle(
color: Colors.white,
fontSize: 10,
),
textAlign: TextAlign.center,
),
),
);
}