如何在flutter上获取Cloud Firestore上的文档id

dependencies:
  flutter:
    sdk: flutter
  firebase_core: ^1.0.0
  cloud_firestore: ^2.2.0

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

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

String getDocumentId() {
  FirebaseFirestore firestore = FirebaseFirestore.instance;
  CollectionReference collectionRef = firestore.collection('collection_name');
  
  // 通过获取集合引用，并使用`.get()`方法获取文档快照
  collectionRef.get().then((QuerySnapshot snapshot) {
    snapshot.docs.forEach((DocumentSnapshot doc) {
      String docId = doc.id;
      // 在这里可以处理文档ID，或者将其返回给调用方
      return docId;
    });
  }).catchError((error) {
    print("Failed to get document ID: $error");
  });
}