Question

嗨，flutter 和 firebase 新手，我尝试做的是简单的注册新用户，然后使用自定义 id 将其信息添加到云 Firestore 并添加子集合名称“通知” 这里是代码示例..

final _auth = FirebaseAuth.instance;
  final _ref = FirebaseFirestore.instance;
  final userCollections = FirebaseFirestore.instance.collection("users");
  Future<void> SignupToColud(
      {@required String name = "",
      @required String email = "",
      @required String pass = ""}) async {
    try {
      await _auth
          .createUserWithEmailAndPassword(email: email, password: pass)
          .then((value) {
        String userId = value.user.uid;
        if (userId != null) {
          userCollections.doc(userId).set({'name': name, 'email': email});
          userCollections
              .doc(userId)
              .collection("notifications")
              .add({'txt': 'welcome you registered as new user succefully'});
        } else {
          throw Error();
        }
      });
      // first sign up to cloud if success

      //then add to users collections
    } catch (e) {
      print(e.toString());
    }
  }


i got this error !!
    lib/Sign_up.dart:24:36: Error: Property 'uid' cannot be accessed on 'User?' because it is potentially null.
 - 'User' is from 'package:firebase_auth/firebase_auth.dart' ('/C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-1.2.0/lib/firebase_auth.dart').
Try accessing using ?. instead.
        String userId = value.user.uid;
                               ^^^

this is pubspec.yaml file information
environment:
sdk: ">=2.12.0 <3.0.0"
dependencies:

    lib/Sign_up.dart:24:36: Error: Property 'uid' cannot be accessed on 'User?' because it is potentially null.
 - 'User' is from 'package:firebase_auth/firebase_auth.dart' ('/C:/src/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-1.2.0/lib/firebase_auth.dart').
Try accessing using ?. instead.
        String userId = value.user.uid;
                               ^^^

我真的不知道这个问题以及如何解决它:(

Answer 1

错误来自这一行：

String userId = value.user.uid;

正如错误所说的 value.user 是一个 User?，这意味着它可以是一个 User 对象或它可以是 null。您的代码需要处理这个可以为 null 的事实，因为只有您可以决定在这种情况下做什么。

我想你想要什么：

  _auth
      .createUserWithEmailAndPassword(email: email, password: pass)
      .then((value) {
    if (value.user != null) {
      String userId = value.user!.uid;
      userCollections.doc(userId).set({'name': name, 'email': email});

所以这会检查 value.user 是否为空（而不是检查 userId。如果 value.user 不为空，则 uid 保证有一个值，所以我们可以在写操作中使用它。

错误：无法在“用户？”上访问属性“uid”因为它可能为空

1 个答案: