Flutter |如何在任何覆盖图上显示AlertDialog？

import 'package:flutter/material.dart';

class OverlayAlertDialog extends StatefulWidget {
  @override
  _OverlayAlertDialogState createState() => _OverlayAlertDialogState();
}

class _OverlayAlertDialogState extends State<OverlayAlertDialog> {
  OverlayEntry _overlayEntry;
  bool _isAlertDialogVisible = false;
  
  @override
  void initState() {
    super.initState();
    _overlayEntry = _createOverlayEntry();
  }
  
  @override
  void dispose() {
    _overlayEntry.remove();
    super.dispose();
  }
  
  OverlayEntry _createOverlayEntry() {
    return OverlayEntry(
      builder: (context) => AlertDialog(
        title: Text('Title'),
        content: Text('Content'),
        actions: [
          FlatButton(
            child: Text('OK'),
            onPressed: () {
              setState(() {
                _isAlertDialogVisible = false;
              });
            },
          ),
        ],
      ),
    );
  }
  
  void _toggleAlertDialog() {
    setState(() {
      _isAlertDialogVisible = !_isAlertDialogVisible;
      if (_isAlertDialogVisible) {
        Overlay.of(context).insert(_overlayEntry);
      } else {
        _overlayEntry.remove();
      }
    });
  }
  
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: _toggleAlertDialog,
      child: Container(
        // 覆盖图的内容
      ),
    );
  }
}

OverlayAlertDialog(),