如何将数据从firebase异步请求中保存在全局变量中

Question

我知道这已经在堆栈上溢出了几次，但我似乎找不到我想要的答案。我试图将数据库中的数据存储在全局变量中。有关详细信息，请参见下面的代码。

我尝试添加一个完整的处理程序并在线遵循步骤，但是这样做，观察者请求停止工作。

我之前拥有的：

class ItemsTableViewController: UITableViewController {
    let listToUsers = "ListToUsers"
    var user: User!
    let ref = Database.database().reference()
    override func viewDidLoad() {
        super.viewDidLoad()
        let defaultUser = User()
        ref.child("users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
            let value = snapshot.value as? NSDictionary
            defaultUser.uid = uid
            defaultUser.email = value?["email"] as? String ?? ""
            defaultUser.name = value?["name"] as? String ?? ""
            defaultUser.grad = value?["grad"] as? Int ?? 0
            defaultUser.number = value?["number"] as? String ?? ""
            defaultUser.image = UIImage(named: value?["image"] as? String ?? "")!
            completion(defaultUser)
        }) { (error) in
            print("hello")
            print(error.localizedDescription)
        }
        self.user = defaultUser
    }
}

我尝试的东西仍然没有起作用：

class ItemsTableViewController: UITableViewController {
    // MARK: Constants
    let listToUsers = "ListToUsers"
    // MARK: Properties
    var user: User!
    let ref = Database.database().reference()
    override func viewDidLoad() {
        super.viewDidLoad()
        let use = Auth.auth().currentUser?.uid
        self.getUserData(uid:use!) { (user) -> () in
            self.user = user
        }
}
func getUserData(uid:String , completion: @escaping (User) -> ()) {
        ref.child("users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
                let value = snapshot.value as? NSDictionary
                let defaultUser = User()
                defaultUser.uid = uid
                defaultUser.email = value?["email"] as? String ?? ""
                defaultUser.name = value?["name"] as? String ?? ""
                defaultUser.grad = value?["grad"] as? Int ?? 0
                defaultUser.number = value?["number"] as? String ?? ""
                defaultUser.image = UIImage(named: value?["image"] as? String ?? "")!
                completion(defaultUser)
        }){ (error) in
            print("hello")
            print(error.localizedDescription)
        }
    }

Answer 1

firebase是异步的，self.user = defaultuser在第一个代码块中要在firebase有机会返回数据之前被调用。

数据仅在firebase调用后的封闭中有效。因此，这是解决它的方法。哦，删除该错误代码，不需要。

假设像这样的用户结构

users
  uid_0
    name: "some name"
    email: "some email"

和在UID_0中读取的代码并填充全局(即类var(用户

class MyUser {
    var uid = ""
    var name = ""
    var email = ""
    init(aUid: String, aName: String, aEmail: String) {
        self.uid = aUid
        self.name = aName
        self.email = aEmail
    }
}
var user: MyUser!
func readOneUser() {
    let uid = "uid_0"
    let thisUserRef = self.ref.child("users").child(uid)
    thisUserRef.observeSingleEvent(of: .value, with: { snapshot in
        //let uid = snapshot.key if you don't know the uid, it will be the key to the node
        let name = snapshot.childSnapshot(forPath: "name").value as? String ?? "No Name"
        let email = snapshot.childSnapshot(forPath: "email").value as? String ?? "No Email"
        self.user = MyUser(aUid: uid, aName: name, aEmail: email)
        print(self.user.name) //do something with the user here
    })
}

和这条线

defaultUser.image = UIImage(named: value?["image"] as? String ?? "")!

需要解决，但我不知道意图是什么。如果发生这种情况，它可能最终成为nil

defaultUser.image = UIImage(named: "")!

因此，您可能需要使用某种默认图像填充它或提供错误处理，以防万一。