我正在尝试获取在警报子节点中写入的 autoId 并将其转换为字符串以便从问题节点中获取此 autoId 以获取其中的信息 - 我的代码运行但不打印/工作

(当前用户autoId是alert节点的第一个子节点，userId是来自“objectId”/questions的第二个子节点的字符串)。这是我的代码:

@IBOutlet weak var statementAnswered: UILabel
@IBOutlet weak var number1Label: UIButton!
@IBOutlet weak var number2Label: UIButton!
@IBOutlet weak var number3Label: UIButton!
@IBOutlet weak var number4Label: UIButton!

 guard let currentUser = Auth.auth().currentUser?.uid else { return }
 let ref = Database.database().reference()

    //enter alert node to get the new Id under the current user node
    let userRef = ref.child("alert").child(currentUser)
    userRef.observe(.childAdded, with: { (snapshot) in
        let uniqueKey = snapshot.key
        print(uniqueKey)
        guard let senderDetails = snapshot.childSnapshot(forPath: "from").value as? String else { return }
        guard let userID = snapshot.childSnapshot(forPath: "objectID").value as? String else { return }
        print(senderDetails)
        print(userID)

        let questionNotification = ref.child("questions").child(senderDetails).child(userID)
        questionNotification.observeSingleEvent(of: .value, with: { (snapshot) in
            let value = snapshot.value as? NSDictionary
            let statement = value?["statement"] as! String
            let number1 = value?["number 1"] as! String
            let number2 = value?["number 2"] as! String
            let number3 = value?["number 3"] as! String
            let number4 = value?["number 4"] as! String
            print(statement)
            print(number1)
            print(number2)
            print(number3)
            print(number4)

            self.statementAnswered.text = question
            self.number1Label.setTitle(number1, for: .normal)
            self.number2Label.setTitle(number2, for: .normal)
            self.number3Label.setTitle(number3, for: .normal)
            self.number4Label.setTitle(number4, for: .normal)
        })
    }, withCancel: nil)

这是 JSON 结构的片段:

 "alert" : {
    "FjS4wUpXAUa5aWwXkjvujHxE4He2" : {
      "-La2uIRfXs15WP8bEfQo" : {
        "from" : "Gmg1ojNoBiedFPRNSL4sBZz2gSx2",
        "objectId" : "-La2uIRPzNXnamX4QLER",
        "timestamp" : 1552696293
      }
    }
  },
  "questions" : {
    "Gmg1ojNoBiedFPRNSL4sBZz2gSx2" : {
      "-La2uIRPzNXnamX4QLER" : {
        "number 1" : "4444",
        "number 2" : "1111",
        "number 3" : "2222",
        "number 4" : "3333",
        "statement" : "favourite number",
        "selected" : "FjS4wUpXAUa5aWwXkjvujHxE4He2"
      }
    }
  },

感谢任何帮助!

更新:

我已经更新了代码，它在控制台上打印了以下内容(应用程序中用户的 autoId):

[Snap (CjeP35ceAQZJuUPhm7U1eF3Yq4F3) 1, Snap 
(FjS4wUpXAUa5aWwXkjvujHxE4He2) 1, Snap (FoFQDAGGX9hntBiBdXYCBHd8yas2) 
1, Snap (PqMkClaPM3W8k7ZSgzAHb3yne5D3) 1]
[Snap (CjeP35ceAQZJuUPhm7U1eF3Yq4F3) 1, Snap 
(FjS4wUpXAUa5aWwXkjvujHxE4He2) 1, Snap (FoFQDAGGX9hntBiBdXYCBHd8yas2) 
1, Snap (PqMkClaPM3W8k7ZSgzAHb3yne5D3) 1]
[Snap (CjeP35ceAQZJuUPhm7U1eF3Yq4F3) 1, Snap 
(FjS4wUpXAUa5aWwXkjvujHxE4He2) 1, Snap (FoFQDAGGX9hntBiBdXYCBHd8yas2) 
1, Snap (PqMkClaPM3W8k7ZSgzAHb3yne5D3) 1]

(我会继续尝试让我的断点起作用，以查看问题所在并在此处更新它(如果起作用)

提前致谢

更新:

我已经更改了数据库的结构，这样“问题”就不会保存在当前用户(回答问题的人)的 autoId 下，而是它只是创建的随机 ID，尽管我不这样做，但它仍然有效'认为这是最有效的方法

最佳答案

问题 1:

userRef.child(uniqueKey).observeSingleEvent(of: .value, with: { snapshot })

无需再次观察用户引用，因为您已经从观察 Alert 节点中获取了所需的信息。

问题2:

let questionNotification = self.ref.child("questions").child(senderDetails).child(self.userId)

在这一行中，您将 userID 引用到 self。查看您的 JSON 很明显，该字段将是动态的，因此在全局范围内对其进行 delcaring 是不明智的。

警告:

您需要处理命名约定。您分配的变量名称甚至与您收到的 JSON 响应都不接近。当您的项目变得更大时，如果您遇到任何错误，您将很难找到问题，因为您无法确定是哪个领域导致的。另外，请查看 Codable 协议(protocol)。它将使您的编码和解码 JSON 对象的生活更轻松。

解决方案:

guard let currentUser = Auth.auth().currentUser?.uid else { return }
    let ref = Database.database().reference()

    //enter alert node to get the new Id under the current user node
    let userRef = ref.child("alert").child(currentUser)
    userRef.observe(.childAdded, with: { (snapshot) in
        let uniqueKey = snapshot.key
        print(uniqueKey)
        guard let senderDetails = snapshot.childSnapshot(forPath: "from").value as? String else { return }
        guard let userID = snapshot.childSnapshot(forPath: "objectID").value as? String else { return }
        print(senderDetails)
        print(userID)

        let questionNotification = ref.child("questions").child(senderDetails).child(userID)
        questionNotification.observeSingleEvent(of: .value, with: { (snapshot) in
            let value = snapshot.value as? NSDictionary
            let statement = value?["statement"] as! String
            let number1 = value?["number 1"] as! String
            let number2 = value?["number 2"] as! String
            print(statement)
            print(number1)
            print(number2)
        })
    }, withCancel: nil)

关于ios - 进入一个子节点获取进入另一个子节点所需的信息，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/55189135/