flutter pub add convex_bottom_bar     

environment:
  sdk: '>=2.12.0 <3.0.0'
dependencies:
  flutter:
    sdk: flutter
  cupertino_icons: ^1.0.2
  convex_bottom_bar: ^3.0.0

import 'package:convex_bottom_bar/convex_bottom_bar.dart';

Scaffold(
  bottomNavigationBar: ConvexAppBar(
    items: [
      TabItem(icon: Icons.home, title: 'Home'),
      TabItem(icon: Icons.map, title: 'Discovery'),
      TabItem(icon: Icons.add, title: 'Add'),
      TabItem(icon: Icons.message, title: 'Message'),
      TabItem(icon: Icons.people, title: 'Profile'),
    ],
    initialActiveIndex: 2,//optional, default as 0
    onTap: (int i) => print('click index=$i'),
  )
);

  int selectedpage = 0;
  final _pageList= [Home(), Message(), Persion(), Detail()];

appBar: AppBar(
  centerTitle: true,
  title: Text('Convex Bottom Bar'),
),

bottomNavigationBar: ConvexAppBar(
  items: [
    TabItem(icon: Icons._home_, title: 'Home'),
    TabItem(icon: Icons._favorite_, title: 'Favorite'),
    TabItem(icon: Icons._shopping_cart_, title: 'Cart'),
    TabItem(icon: Icons._person_, title: 'Profile'),
  ],
  initialActiveIndex: selectedpage,
  onTap: (int index){
      setState(() {
        selectedpage = index;
      });
  },
),

import 'package:convex_bottom_bar/convex_bottom_bar.dart';
import 'package:flutter/material.dart';
import 'detail.dart';
import 'home.dart';
import 'message.dart';
import 'persion.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.teal,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int selectedpage = 0;
  final _pageNo = [Home(), Message(), Persion(), Detail()];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: Text('Convex Bottom Bar'),
      ),
      body: _pageNo[selectedpage],
      bottomNavigationBar: ConvexAppBar(
           color: Colors.white,
        activeColor: Colors.red,
        backgroundColor: Colors.orange,
        items: [
          TabItem(icon: Icons.person, title: '新'),
          TabItem(icon: Icons.favorite, title: '年'),
          TabItem(icon: Icons.brush, title: '快'),
          TabItem(icon: Icons.car_rental, title: '樂'),
        ],
        initialActiveIndex: selectedpage,
        onTap: (int index) {
          setState(() {
            selectedpage = index;
          });
        },
      ),
    );
  }
}

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

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

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

class _HomeState extends State<Home> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: Text('歡迎來到這兒'),
      ),
      body: Center(
        child: Text(
          '早起的年輕人',
          style: TextStyle(fontSize: 60, fontWeight: FontWeight.bold),
        ),
      ),
    );
  }
}

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

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

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

class _MessageState extends State<Message> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: Text('這是當前頁的AppBar'),
      ),
      body: Center(
        child: Text(
          '因為硬核，所以堅果！',
          style: TextStyle(fontSize: 60, fontWeight: FontWeight.bold),
        ),
      ),
    );
  }
}

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

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

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

class _PersionState extends State<Persion> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(  appBar: AppBar(
        centerTitle: true,
        title: Text('公眾號'),
      ),
      body: Center(
        child: Text(
          '大前端之旅',
          style: TextStyle(fontSize: 60, fontWeight: FontWeight.bold),
        ),
      ),
    );
  }
}

// ignore: file_names
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';

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

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

class _DetailState extends State<Detail> {
  String image =
      "https://luckly007.oss-cn-beijing.aliyuncs.com/image/image-20220114111115931.png";
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: Text('掃碼關注'),
      ),
      body: Center(
        child: new Image(image: new NetworkImage(image)),
      ),
    );
  }
}