在Flutter 3.3.9中，我使用Streambuilder从Firestore数据库中获取一条记录，我使用以下代码段来完成此操作：

StreamBuilder<Object>(
                stream: FirebaseFirestore.instance
                    .collection('users')
                    .doc(userId)
                    .snapshots(),
                builder: (context, snapshot) {
                  if (snapshot.connectionState == ConnectionState.waiting) {
                    return Text('Loading...');
                  }
                  return Text(
                    snapshot.data!.doc['username'], // This line is marked as error bexcause "doc" is illegal.
                    ),
                  );
                },
              ),

snapshot.data!.doc['username']给出以下错误：
没有为类型"Object"定义getter "doc"。
I verified that the 'Object' is of type "AsyncSnapshot" (=snapshot.runtimeType). It looks like the only getters available for the snapshot.data are hashCode, runtimeType, toString(), and noSuchMethod(..).
我试过了

snapshot.data!().doc['username'],

但这也不管用，错误是"表达式没有求值为函数，所以不能调用"
我可以在不使用StreamBuilder的情况下访问数据。

final docRef = FirebaseFirestore.instance
                      .collection('users')
                      .doc(userId);

                  docRef.get().then(
                    (DocumentSnapshot doc) {
                      final data = doc.data() as Map<String, dynamic>;
                      print(data['username']);
                    },
                    onError: (e) => print("Error getting document: $e"),
                  );