\'Future<String?>\' flutter 实例

【问题标题】：Instance of 'Future<String?>' flutter\'Future<String?>\' flutter 实例
【发布时间】：2023-02-11 21:35:50
【问题描述】：

为什么返回“Future<String?>”实例而不是字符串值？

Future<String?> getUser() async {
    User user = await FirebaseAuth.instance.currentUser!;
    FirebaseFirestore firestore = await FirebaseFirestore.instance;
    String uid = user.uid;
    String? userName;

    // to get username from firebase
    return firestore
        .collection("users")
        .doc(uid)
        .get()
        .then((value) {
      if (value.exists) {
        var data = value.data();
        userName = data?["name"];
        print("There is data :$userName");
      } else {
        print("There no Data!");
      }
      return Future.value(userName);
    });
  }

我正在尝试获取字符串值？

【问题讨论】：

标签： flutter dart google-cloud-firestore

【解决方案1】：

这将是

  return await firestore.collection("users")....get()

获取数据而不是未来。

我也建议不要混合等待和.then。

Future<String?> getUser() async {
  User user = FirebaseAuth.instance.currentUser!;
  FirebaseFirestore firestore = FirebaseFirestore.instance;
  String uid = user.uid;
  String? userName;

  // to get username from firebase
  final value = await firestore.collection("users").doc(uid).get();
  if (value.exists) {
    var data = value.data();
    userName = data?["name"];
    print("There is data :$userName");
  } else {
    print("There no Data!");
  }
  return userName;
}

【讨论】：