Firebase 和 Swift：在 Firebase 上更新后，在应用上实时更新用户信息

Question

我的应用要求您至少关注四个人（或者按钮显示“关注至少 4 个朋友”）才能开始回答关于您关注的人的多项选择式问答。现在，每当用户关注某人时，它都会在 firebase 上更新，但他们关注的人不会实时显示在 MCQ/Q&A 页面上，除非我从一开始就运行该应用程序。

如何让它实时更新，而不必从头开始重新运行？

更新：

我已将之前的 observeSingleEvent 函数更改为使用 DataEventType.value 的观察函数，它比以前更好，因为它会在我关注和取消关注人时更新，但前提是用户有超过 4 个关注者。

现在，如果我取消关注 4 个以下的人，它会显示“正确关注至少 4 个朋友”，但当我关注 4 个或更多时，按钮会调用 4 个随机用户，但会冻结且无法按下。

此外，当我尝试在两个观察功能的底部添加解除功能时 - 它会出错并且不会让我进入页面

这是更新后的代码（我希望我解释正确，如果这看起来像一个愚蠢的问题，我很抱歉我感谢任何帮助/解释） - 提前致谢 :)

viewDidLoad 中调用的函数是：

var ref: DatabaseReference = Database.database().reference()
var currNames: [String] = []
var currIds: [String] = []
let imageViewA = UIImageView()
let imageViewB = UIImageView()
let imageViewC = UIImageView()
let imageViewD = UIImageView()

func getFourRandomNodesAndPrintUserName() {
    self.currNames = []
    self.currIds = []

    var myKeyArray = [String]()
    guard let uid = Auth.auth().currentUser?.uid else {
        return
    }

    let ref = self.ref.child("following").child(uid) //retreives all nodes in the following node
    ref.observe(DataEventType.value, with: { (snapshot) in
        print(snapshot.children.allObjects)
        for child in snapshot.children { //build the array of keys
            let snap = child as! DataSnapshot
            let key = snap.key
            myKeyArray.append(key)
    }

        var randomKeyArray = [String]()
        let numFollowers = min(4, myKeyArray.count)
        for _ in 0..<numFollowers { //will iterate four times
            let count = myKeyArray.count //get the number of elements
            let randomInt = Int.random(in: 0..<count) //get a random index for the array
            let randomUserKey = myKeyArray[randomInt]
            randomKeyArray.append(randomUserKey)
            myKeyArray.remove(at: randomInt) //remove that object so it's not selected again
        }

        let numberOfKeys = randomKeyArray.count
        var namesRemaining = numberOfKeys
        var names = [String]()
        var namesWithUrl = [String : String]()
        var profileImages = [String]()

        for i in 0..<numberOfKeys {
            let thisUserKey = randomKeyArray[i]
            let userRef = self.ref.child("users").child(thisUserKey)
            userRef.observeSingleEvent(of: .value, with: { snapshot in
                let name = snapshot.childSnapshot(forPath: "fullname").value as! String
                let profileImageUrl = snapshot.childSnapshot(forPath: "profileImageUrl").value as! String
                print(name)
                print(profileImageUrl)
                namesRemaining -= 1
                names.append(name)
                profileImages.append(profileImageUrl)
                namesWithUrl[name] = profileImageUrl

                self.currIds.append(thisUserKey)

                if numFollowers <= 3 {
                    self.optionA.setTitle("Follow\nat least\n4 friends!", for: .normal)
                    self.optionA.isEnabled = false

                    self.optionB.setTitle("Follow\nat least\n4 friends!", for: .normal)
                    self.optionB.isEnabled = false

                    self.optionC.setTitle("Follow\nat least\n4 friends!", for: .normal)
                    self.optionC.isEnabled = false

                    self.optionD.setTitle("Follow\nat least\n4 friends!", for: .normal)
                    self.optionD.isEnabled = false
                }
                else if namesRemaining == 0 {
                    self.currNames = names
                    self.optionA.setTitle(names[0], for: .normal)
                    let optionAUrl = URL.init(string: namesWithUrl[names[0]]!)
                    self.imageViewA.sd_setImage(with: optionAUrl)

                    self.optionB.setTitle(names[1], for: .normal)
                    let optionBUrl = URL.init(string: namesWithUrl[names[1]]!)
                    self.imageViewB.sd_setImage(with: optionBUrl)

                    self.optionC.setTitle(names[2], for: .normal)
                    let optionCUrl = URL.init(string: namesWithUrl[names[2]]!)
                    self.imageViewC.sd_setImage(with: optionCUrl)

                    self.optionD.setTitle(names[3], for: .normal)
                    let optionDUrl = URL.init(string: namesWithUrl[names[3]]!)
                    self.imageViewD.sd_setImage(with: optionDUrl)
                }
                //self.dismiss(animated: true, completion: nil) //it works when i don't include this otherwise there is a bug

            })
        }
        //self.dismiss(animated: true, completion: nil) //it works when i don't include this otherwise there is a bug out
    })
}

更新：

我从 firebase 复制了我的 Realtime DB JSON 结构的 sn-p：

"following" : {
      "MJxCFUX0jpXJD1a2u0iqt6xSAdB3" : {
      "5W6Qf4cJKQb5nY1PthMUelHLShy2" : true,
      "GU03rUQPrIX4zleX1S8L8anSWmn2" : true,
      "MfeIehKJKzS2Cf0kA0JTmHZGWSu1" : true
    },
      "MfeIehKJKzS2Cf0kA0JTmHZGWSu1" : {
      "5W6Qf4cJKQb5nY1PthMUelHLShy2" : true,
      "GU03rUQPrIX4zleX1S8L8anSWmn2" : true,
      "MJxCFUX0jpXJD1a2u0iqt6xSAdB3" : true,
      "nZLf70wvZUYqrAExXmnSX9G7Rar2" : true
    },
      "nZLf70wvZUYqrAExXmnSX9G7Rar2" : {
      "5W6Qf4cJKQb5nY1PthMUelHLShy2" : true,
      "FwUzqbn49FP5jS5mIuaAEnrxvpj2" : true,
      "GU03rUQPrIX4zleX1S8L8anSWmn2" : true,
      "MJxCFUX0jpXJD1a2u0iqt6xSAdB3" : true,
      "MfeIehKJKzS2Cf0kA0JTmHZGWSu1" : true
    }


"users" : {
     "5W6Qf4cJKQb5nY1PthMUelHLShy2" : {
      "email" : "aaaa@gmail.com",
      "fullname" : "Aaaa",
      "fullname_lowercase" : "aaaa",
      "profileImageUrl" : "https://firebasestorage.googleapis.com/v0/b/pinion-4896b.appspot.com/o/profile_image%2F5W6Qf4cJKQb5nY1PthMUelHLShy2?alt=media&token=eba41189-98dc-45d0-bccc-769cc8fa872f"
    },
     "FwUzqbn49FP5jS5mIuaAEnrxvpj2" : {
      "email" : "ffff@gmail.com",
      "fullname" : "Ffff",
      "fullname_lowercase" : "ffff",
      "profileImageUrl" : "https://firebasestorage.googleapis.com/v0/b/pinion-4896b.appspot.com/o/profile_image%2FFwUzqbn49FP5jS5mIuaAEnrxvpj2?alt=media&token=55649e15-4e6c-4b44-b804-1b4a9e8e4272"
    },
}

Answer 1

因此您可以使用observ 函数代替observeSingleEvent。 来自谷歌文档的示例： postRef.observe(DataEventType.value, with: { (snapshot) in let postDict = snapshot.value as? [String : AnyObject] ?? [:] // ... })

DataEventType（它是枚举）有下一个值： /// A new child node is added to a location. FIRDataEventTypeChildAdded, /// A child node is removed from a location. FIRDataEventTypeChildRemoved, /// A child node at a location changes. FIRDataEventTypeChildChanged, /// A child node moves relative to the other child nodes at a location. FIRDataEventTypeChildMoved, /// Any data changes at a location or, recursively, at any child node. FIRDataEventTypeValue

Observ 函数的工作方式类似于侦听器-观察者模式，所以不要忘记在观察事件时关闭订阅。