Flutter:如何显示bottomNavigationBar背后的内容

import 'package:flutter/material.dart';

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

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

class MainPage extends StatefulWidget {
  @override
  _MainPageState createState() => _MainPageState();
}

class _MainPageState extends State<MainPage> {
  int _currentIndex = 0;
  PageController _pageController = PageController();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter App'),
      ),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _currentIndex,
        onTap: (index) {
          setState(() {
            _currentIndex = index;
            _pageController.animateToPage(
              index,
              duration: Duration(milliseconds: 300),
              curve: Curves.ease,
            );
          });
        },
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Home',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.search),
            label: 'Search',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.person),
            label: 'Profile',
          ),
        ],
      ),
      body: PageView(
        controller: _pageController,
        onPageChanged: (index) {
          setState(() {
            _currentIndex = index;
          });
        },
        children: [
          Container(
            child: Center(
              child: Text('Home Page'),
            ),
          ),
          Container(
            child: Center(
              child: Text('Search Page'),
            ),
          ),
          Container(
            child: Center(
              child: Text('Profile Page'),
            ),
          ),
        ],
      ),
    );
  }
}