Это очень просто. Просто измените цвет в зависимости от выбранного индекса.
Здесь вы go
import 'package:flutter/material.dart';
final Color darkBlue = Color.fromARGB(255, 18, 32, 47);
void main() {
runApp(MyApp());
}
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
debugShowCheckedModeBanner: false,
home: HomePage(),
);
}
}
class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> {
int _tabIndex = 0;
var colors = [Colors.blue, Colors.red, Colors.orange];
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('Dash'),
backgroundColor: colors[_tabIndex],
),
body: Container(),
bottomNavigationBar: BottomNavigationBar(
currentIndex: _tabIndex,
onTap: (value) => setState(() => _tabIndex = value),
type: BottomNavigationBarType.shifting,
unselectedItemColor: Theme.of(context).unselectedWidgetColor,
items: [
BottomNavigationBarItem(
icon: Icon(Icons.dashboard),
title: Text('Dash'),
backgroundColor: colors[0]),
BottomNavigationBarItem(
icon: Icon(Icons.insert_chart),
title: Text('Data'),
backgroundColor: colors[1]),
BottomNavigationBarItem(
icon: Icon(Icons.monetization_on),
title: Text('Income'),
backgroundColor: colors[2]),
]),
);
}
}
Смотрите живую демонстрацию здесь .