Flutter/Dart -获取在文本小部件中使用的PageView.Builder的索引号？

import 'package:flutter/material.dart';

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

class _MyPageState extends State<MyPage> {
  PageController _pageController = PageController();
  int _currentIndex = 0;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('PageView Example'),
      ),
      body: Column(
        children: [
          Text('当前页面索引号: $_currentIndex'),
          Expanded(
            child: PageView.builder(
              controller: _pageController,
              itemCount: 3,
              itemBuilder: (context, index) {
                return Container(
                  color: Colors.blue,
                  child: Center(
                    child: Text(
                      '页面 $index',
                      style: TextStyle(fontSize: 24, color: Colors.white),
                    ),
                  ),
                );
              },
              onPageChanged: (index) {
                setState(() {
                  _currentIndex = index;
                });
              },
            ),
          ),
        ],
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    home: MyPage(),
  ));
}