方案：1.BottomNavigationBar+PageView

 class MainPage extends StatefulWidget {
   @override
  State<StatefulWidget> createState() {
    return MainPageState();
  }
 }

 class MainPageState extends State<MainPage> {
   int _currentIndex;
   List<Widget> _pages;
   PageController _controller;

   List<BottomNavigationBarItem> getItems() {
     return [
       BottomNavigationBarItem(icon: Icon(Icons.home), title: Text("Home")),
       BottomNavigationBarItem(icon: Icon(Icons.adb), title: Text("Adb")),
       BottomNavigationBarItem(icon: Icon(Icons.person), title: Text("Person")),
     ];
   }

   @override
  void initState() {
    super.initState();
    _currentIndex = 0;
    _pages = List()..add(Page1("第一页"))..add(Page2("第二页"))..add(Page3("第三页"));
    _controller = PageController(initialPage: 0);
  }

  @override
  void dispose() {
    super.dispose();
    _controller.dispose();
  }

  
   @override
   Widget build(BuildContext context) {
     return Scaffold(
       body: PageView.builder(
         physics: NeverScrollableScrollPhysics(),
         controller: _controller,
         itemCount: _pages.length,
         itemBuilder: (context, index) {
           return _pages[index];
         },
         onPageChanged: _pageChange,
       ),
       bottomNavigationBar: BottomNavigationBar(
         items: getItems(),
         currentIndex: _currentIndex,
         onTap: onTap,
       ),
     );
   }

   void onTap(int index) {
     _controller.jumpToPage(index);
   }

   void _pageChange(int index) {
     if (index  != _currentIndex) {
       setState(() {
         _currentIndex = index;
       });
     }
   }
 }

方案：2.BottomNavigationBar+IndexedStack

class MainPage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return MainPageState();
  }
}

class MainPageState extends State<MainPage> {
  int _currentIndex;
  List<Widget> _pages;

  List<BottomNavigationBarItem> getItems() {
     return [
       BottomNavigationBarItem(icon: Icon(Icons.home), title: Text("Home")),
       BottomNavigationBarItem(icon: Icon(Icons.adb), title: Text("Adb")),
       BottomNavigationBarItem(icon: Icon(Icons.person), title: Text("Person")),
     ];
   }

   @override
  void initState() {
    super.initState();
    _currentIndex = 0;
    _pages = List()..add(Page1("第一页"))..add(Page2("第二页"))..add(Page3("第三页"));
  }

   @override
  Widget build(BuildContext context) {
    return Scaffold(
      bottomNavigationBar: BottomNavigationBar(
        type: BottomNavigationBarType.fixed,
        currentIndex: _currentIndex,
        items: getItems(),
        onTap: onTabTapped,
      ),
      body: IndexedStack(
        index: _currentIndex,
        children: _pages,
      ),
    );
  }

  void onTabTapped(int index) {
    setState(() {
      _currentIndex = index;
    });
  }
}

其他，用到的文件

0.

import 'package:flutter/material.dart';
 
 void main() => runApp(MyApp());

 class MyApp extends StatelessWidget {
   @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Demo",
      home: MainPage(),
    );
  }
 }

1.Page1 & Page1State

class Page1 extends StatefulWidget {
   String _title;
   Page1(this._title);

   @override
  State<StatefulWidget> createState() {
    return Page1State();
  }
 }

 class Page1State extends State<Page1> with AutomaticKeepAliveClientMixin {
   int _count = 0;

   @override
  bool get wantKeepAlive => true;

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return Scaffold(
      appBar: AppBar(
        title: Text(widget._title),
      ),
      body: Center(
        child: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Text(widget._title + ":点一下加1：$_count"),
          MaterialButton(
            child: Text("跳转"),
            color: Colors.pinkAccent,
            onPressed: () {
              Navigator.push(
                context, 
                MaterialPageRoute(builder: (context) {
                  return NewPage();
                }));
            },
          )
        ],
      ),
      ),
      floatingActionButton: FloatingActionButton(
        heroTag: widget._title,
        child: Icon(Icons.add),
        onPressed: addAction,
      ),
    );
  }

  void addAction() {
    setState(() {
      _count++;
    });
  }
 }

其余的 Page2 & Page2State，Page3 & Page3State 也类似上述代码。

2.NewPage

class NewPage extends StatelessWidget {
   @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("新的界面"),
      ),
      body: Center(
        child: Text("我是一个新的界面"),
      ),
    );
  }
 }