如何在Flutter Firebase中创建文档时将文档id保存在文档字段中

import 'package:flutter/material.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Firebase Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Firebase Demo'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Create Document'),
          onPressed: () {
            createDocument();
          },
        ),
      ),
    );
  }

  void createDocument() async {
    CollectionReference collection =
        FirebaseFirestore.instance.collection('your_collection');

    Map<String, dynamic> data = {
      'name': 'John Doe',
      'created_at': FieldValue.serverTimestamp(),
      'document_id': '',
    };

    DocumentReference docRef = await collection.add(data);
    String docId = docRef.id;

    await docRef.update({'document_id': docId});
    print('Document created with ID: $docId');
  }
}