如何在AnimatedSwitcher切换后保持键盘在TextField上打开？

import 'package:flutter/material.dart';

class MyPage extends StatefulWidget {
  @override
  _MyPageState createState() => _MyPageState();
}

class _MyPageState extends State<MyPage> {
  int _pageIndex = 0;
  List<Widget> _pages = [
    Page1(),
    Page2(),
  ];

  List<FocusNode> _focusNodes = [
    FocusNode(),
    FocusNode(),
  ];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('AnimatedSwitcher Demo'),
      ),
      body: GestureDetector(
        onTap: () {
          // 点击空白处时，取消TextField的焦点
          FocusScope.of(context).requestFocus(FocusNode());
        },
        child: AnimatedSwitcher(
          duration: Duration(milliseconds: 500),
          child: _pages[_pageIndex],
          transitionBuilder: (child, animation) {
            return FadeTransition(
              opacity: animation,
              child: child,
            );
          },
        ),
      ),
      bottomNavigationBar: BottomNavigationBar(
        currentIndex: _pageIndex,
        onTap: (index) {
          setState(() {
            _pageIndex = index;
            // 切换页面时，将对应的FocusNode设置为焦点
            FocusScope.of(context).requestFocus(_focusNodes[_pageIndex]);
          });
        },
        items: [
          BottomNavigationBarItem(
            icon: Icon(Icons.home),
            label: 'Page 1',
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.settings),
            label: 'Page 2',
          ),
        ],
      ),
    );
  }
}

class Page1 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(16),
      child: TextField(
        focusNode: FocusScope.of(context).focusNode,
        decoration: InputDecoration(
          labelText: 'Page 1',
        ),
      ),
    );
  }
}

class Page2 extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.all(16),
      child: TextField(
        focusNode: FocusScope.of(context).focusNode,
        decoration: InputDecoration(
          labelText: 'Page 2',
        ),
      ),
    );
  }
}