如何在flutter中动态获取单个firestore文档

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

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

Future<DocumentSnapshot> getFirestoreDocument() async {
  // 获取Firestore实例
  FirebaseFirestore firestore = FirebaseFirestore.instance;

  // 获取指定文档的引用
  DocumentReference documentReference = firestore.collection('collectionName').doc('documentId');

  // 获取文档数据
  DocumentSnapshot documentSnapshot = await documentReference.get();
  
  // 返回文档快照
  return documentSnapshot;
}

void fetchData() async {
  DocumentSnapshot snapshot = await getFirestoreDocument();
  // 处理文档数据
  if (snapshot.exists) {
    Map<String, dynamic> data = snapshot.data();
    // 对文档数据进行操作
  }
}