其他功能获得价值但不是其他[重复]

Question

在我加载用户的函数中，我可以检索一个值。但是，当我想将它分配给函数外部的变量时，它什么都没有，如登录函数所示。

加载用户函数

func loadUser(userid: String) -> User {
   //print(userid)
   let userid = "56ldZFJiv0dpfaABzo78"
   var user = User()
   let docRef = db.collection("users").document(userid)
   docRef.getDocument { (document, error) in
       if let document = document {
           let first = document.data()!["first"] as! String
           let last = document.data()!["last"] as! String
           let position = document.data()!["position"] as! String
           let company = document.data()!["company"] as! String
           let email = document.data()!["email"] as! String
           let address = document.data()!["address"] as! String
           let userID = document.data()!["userID"] as! String

           //Initalize user
          user =  User(userID: userID,
                                    firstName: first,
                                    lastName: last,
                                    company: company,
                                    address: address,
                                    position: position,
                                    email: email)

           print(user.position)
       } else {
           print("Document does not exist")
       }
   }
   return user
}

登录功能

//MARK: LOGIN
func login() {
    Auth.auth().signIn(withEmail: emailField.text!, password: passwordField.text!) { (user, error) in
        if error == nil{
            //self.performSegue(withIdentifier: "loginToAdmin", sender: self)

            //Load user
            let loggedOnUser = self.loadUser(userid: Auth.auth().currentUser!.uid)
            print(loggedOnUser.userID)
//                let storyBoard: UIStoryboard = UIStoryboard(name: "Main", bundle: nil)
//                let chatViewController = storyBoard.instantiateViewController(withIdentifier: "chatVC") as! UINavigationController
//                self.present(chatViewController, animated: true, completion: nil)
        }
        else {
            DispatchQueue.main.async{
                //Display Alert Message if login failed
                let alertController = UIAlertController(title: "Error", message: error?.localizedDescription, preferredStyle: .alert)
                let defaultAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
                alertController.addAction(defaultAction)
                self.present(alertController, animated: true, completion: nil)
            }
        }
    }
}

对于第一个函数，我得到一个位置值，如打印语句中所述。 对于第二个函数，我的变量“loggedOnUser”为空。

Answer 1

你需要一个完成，因为loadUser 是异步的

func loadUser(userid: String,completion:@escaping(User?) ->()) {
       //print(userid)
       let userid = "56ldZFJiv0dpfaABzo78"
       var user = User()
       let docRef = db.collection("users").document(userid)
       docRef.getDocument { (document, error) in
           if let document = document {
               let first = document.data()!["first"] as! String
               let last = document.data()!["last"] as! String
               let position = document.data()!["position"] as! String
               let company = document.data()!["company"] as! String
               let email = document.data()!["email"] as! String
               let address = document.data()!["address"] as! String
               let userID = document.data()!["userID"] as! String

               //Initalize user
              user =  User(userID: userID,
                                        firstName: first,
                                        lastName: last,
                                        company: company,
                                        address: address,
                                        position: position,
                                        email: email)

               print(user.position)
               completion(user)
           } else {
               print("Document does not exist")
               completion(nil)
           }
       } 
   }

---

打电话

 self.loadUser(userid: Auth.auth().currentUser!.uid) { res in
     if let user = res {
        print(user)
     }
}