Flutter的BottomNavigationBar不能在点击时更新所选项目

我是Flutter的新手，目前正在尝试非常简单的练习以了解基本知识。我刚刚在屏幕底部的BottomNavigationBar创建了一个基本的Home。但是，当我点击一个条形图标时，它不会切换颜色以使其看起来好像被轻击一样。我需要重新加载以更新它。我无法从'MyBottmNavigationBar'类更新图标状态...如果我仅复制/粘贴Flutter.dev示例代码，它将起作用...我需要在代码中修复什么？ 随时指出任何错误或提示！ 提前致谢！

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Home();
  }
}

class Home extends StatefulWidget {
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyScaffold(),
    );
  }
}

class MyScaffold extends StatefulWidget {
  @override
  _MyScaffoldState createState() => _MyScaffoldState();
}

class _MyScaffoldState extends State<MyScaffold> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Hey Flutter'),),
      body: MyListView(),
      bottomNavigationBar: MyBottomNavigationBar(),
    );
  }
}


class MyListView extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ListView(
      padding: const EdgeInsets.all(2),
      children: <Widget>[
        Container(
          height: 50,
          color: Colors.amber[600],
          child: const Center(child: Text('Entry A')),
        ),
        Container(
          height: 50,
          color: Colors.amber[500],
          child: const Center(child: Text('Entry B')),
        ),
        Container(
          height: 50,
          color: Colors.amber[100],
          child: const Center(child: Text('Entry C')),
        ),
        Container(
          height: 50,
          color: Colors.amber[600],
          child: const Center(child: Text('Entry A')),
        ),
      ],
    );
  }
}

class MyBottomNavigationBar extends StatefulWidget {
  MyBottomNavigationBar({Key key}) : super(key: key);

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

class _MyBottomNavigationBarState extends State<MyBottomNavigationBar> {
  int _selectedIndex = 0;
  void _onItemTapped(int index){
    _selectedIndex = index;
    print('Selected: ${_selectedIndex} CurrentIndex: ${index}');
  }
  @override
  Widget build(BuildContext context) {
    return BottomNavigationBar(
      currentIndex: _selectedIndex,
      selectedItemColor: Colors.pink,
      onTap: _onItemTapped,
      items: const <BottomNavigationBarItem>[
        BottomNavigationBarItem(
          icon: Icon(Icons.home),
          title: Text('Home'),
        ),
        BottomNavigationBarItem(
          icon: Icon(Icons.table_chart),
          title: Text('Projects'),
        ),
        BottomNavigationBarItem(
          icon: Icon(Icons.people),
          title: Text('Teams'),
        ),
      ],
    );
  }
}
```