Ios 正在swift中从firebase读取数据，但无法显示数据。可能是可变范围错误

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正在Swift中从firebase读取数据，但无法显示数据。可能是可变范围错误。打印输出（值？[“名称”]为？字符串？？？”是预期结果，但未分配给self.name变量。我相信这是一个范围错误，但我还不确定。非常感谢所有帮助，因为我对iOS和Swift比较陌生。

因为从Firebase接收数据是一项异步任务，所以不能这样做。您必须为此使用完成处理程序

首先添加完成处理程序作为函数的参数，也不需要返回类型

import UIKit
import FirebaseDatabase
import FirebaseAuth
class mapVC: UIViewController {
    var name:String = ""
    var number:String = ""

override func viewDidLoad() {
    super.viewDidLoad()
    self.navigationItem.setHidesBackButton(true, animated:true);
    var dict = fetchData()
    print(dict)

}
func fetchData()->[String:String]{
    var ref: DatabaseReference!
    ref = Database.database().reference()
    var uid:String=""
    var email:String=""
    let user = Auth.auth().currentUser
    if let user = user {
        let uid_local = user.uid
        let email_local = user.email
        uid=uid_local
        email=email_local!
    }
    ref.child("Users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
        let value = snapshot.value as? NSDictionary
        self.name = value?["name"] as? String ?? ""
        print(value?["name"] as? String ?? "")
        self.number = value?["number"] as? String ?? ""
        print(value?["number"] as? String ?? "")
    })
    return(["Name":name,"Number":number,"Email":email,"UID":uid]);
}
}

然后在收到数据时调用completion

func fetchData(_ completion: @escaping ([String:String]) -> ())

现在，您可以通过关闭

fetchData

函数从Firebase访问数据

ref.child("Users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
    ...
    completion(["Name":name,"Number":number,"Email":email,"UID":uid])
})

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注意：从Firebase接收数据之前，您不会有这些数据，因此需要一些时间

因为从Firebase接收数据是一项异步任务，您不能这样做。您必须为此使用完成处理程序

首先添加完成处理程序作为函数的参数，也不需要返回类型

import UIKit
import FirebaseDatabase
import FirebaseAuth
class mapVC: UIViewController {
    var name:String = ""
    var number:String = ""

override func viewDidLoad() {
    super.viewDidLoad()
    self.navigationItem.setHidesBackButton(true, animated:true);
    var dict = fetchData()
    print(dict)

}
func fetchData()->[String:String]{
    var ref: DatabaseReference!
    ref = Database.database().reference()
    var uid:String=""
    var email:String=""
    let user = Auth.auth().currentUser
    if let user = user {
        let uid_local = user.uid
        let email_local = user.email
        uid=uid_local
        email=email_local!
    }
    ref.child("Users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
        let value = snapshot.value as? NSDictionary
        self.name = value?["name"] as? String ?? ""
        print(value?["name"] as? String ?? "")
        self.number = value?["number"] as? String ?? ""
        print(value?["number"] as? String ?? "")
    })
    return(["Name":name,"Number":number,"Email":email,"UID":uid]);
}
}

然后在收到数据时调用completion

func fetchData(_ completion: @escaping ([String:String]) -> ())

现在，您可以通过关闭

fetchData

函数从Firebase访问数据

ref.child("Users").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
    ...
    completion(["Name":name,"Number":number,"Email":email,"UID":uid])
})

---

注意：从Firebase接收数据之前，您不会有这些数据，因此需要一些时间

您是指这样的事情吗？您是指这样的事情吗-