您正在使用StreamBuilder，但流不是stream，而是future。
请看streamBuilder的示例：如果没有reload，您可以在这里直接监听文档中发生的任何更改。根据您的需要调整此设置。

class _UserInformationState extends State<UserInformation> {
  final _usersStream = FirebaseFirestore.instance
      .collection('Users')  // 👈 Change the collection name according to your need 
      .doc(Auth().currentUser!.uid) // 👈 change the document id according to your need
      .snapshots();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(
          stream: _usersStream,
          builder:
              (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
            if (snapshot.hasError) {
              return const Text('Something went wrong');
            }
            if (snapshot.connectionState == ConnectionState.waiting) {
              return const Text("Loading");
            }
            Map<String, dynamic> data =
                snapshot.data!.data()! as Map<String, dynamic>;
            return Text(data['fullName']);
          },
        ),
      ),
    );
  }
}