iOS-Firebase观察单个事件调用两次

我对Firebase和iOS开发相对较新,所以我希望有人能给我一些关于我做错的指导.出于某种原因,我的Observe中的代码块正在运行两次,即使ObserveSingleEvent特别应该在读取初始数据后终止观察.

我想要注意的是,这只发生在我的手机上(iPhone 7 iOS10).当我在模拟器中运行它时,我遇到了一个完全不同的问题,我得到了一个应该调用的调用,但是,当我的视图仍在上一个视图中时调用.本质上,应该在主屏幕加载其视图后调用此函数.但是,在模拟器中,当我在登录屏幕中对我的用户进行身份验证时,如果我没有用户名,则会创建弹出窗口,并且实际上不会将下一个视图显示到主屏幕.

这是引起问题的函数:

func initialSetUp() {
    print("initially set up")
    let userRef = FIRDatabase.database().reference(withPath: "/users/").child("\(uid!)")
    userRef.observeSingleEvent(of: .value, with: { (snapshot) in
        print("observing event")
        print("\(snapshot)")

        if snapshot.hasChild("username"){
           print("user has username")
        } else {
            print("user does not have username")
            //do stuff
            let nameRef = FIRDatabase.database().reference(withPath: "/usernames/")
            let alert = SCLAlertView()
            let appearance = SCLAlertView.SCLAppearance(
                kTitleFont: UIFont(name: "Futura-Medium", size: 20)!,
                kTextFont: UIFont(name: "Futura-Medium", size: 14)!,
                kButtonFont: UIFont(name: "Futura-Bold", size: 14)!,
                showCloseButton: false,
                shouldAutoDismiss: false
            )
            alert.appearance = appearance
            let newName = alert.addTextField("Enter your name")
            alert.addButton("Check name", backgroundColor: UIColor.black, textColor: UIColor.white, showDurationStatus: false) {
                UIApplication.shared.sendAction(#selector(UIResponder.resignFirstResponder), to:nil, from:nil, for:nil)
                if let name = newName.text {
                    if name != "" {
                    //check if username is unique
                        nameRef.child(name.lowercased()).observeSingleEvent(of: FIRDataEventType.value, with: { (snapshot) in
                            print("\(snapshot.value)")
                            if !snapshot.exists() {
                                let alertView = SCLAlertView()
                                alertView.showSuccess("Woohoo!", subTitle: "This username is valid!")
                                print("valid username")
                            } else {
                                let alertView = SCLAlertView()
                                alertView.showError("Sorry :(", subTitle: "This username has already been taken.")
                            }
                        })
                    } else {
                        let alertView = SCLAlertView()
                        alertView.showError("Sorry :(", subTitle: "Your name can't be blank!")
                    }
                }

            }
            alert.addButton("Done", backgroundColor: UIColor.black, textColor: UIColor.white, showDurationStatus: false) {
                UIApplication.shared.sendAction(#selector(UIResponder.resignFirstResponder), to:nil, from:nil, for:nil)
                if let name = newName.text {
                    if name != "" {
                        //check if username is unique
                        nameRef.child(name.lowercased()).observeSingleEvent(of: FIRDataEventType.value, with: { (snapshot) in
                            print("\(snapshot.value)")
                            if !snapshot.exists() {
                                alert.hideView()
                                let alertView = SCLAlertView()
                                alertView.showSuccess("Success!", subTitle: "You're all set to go!")
                                userRef.child("username").setValue(name)
                                nameRef.updateChildValues([name.lowercased(): self.uid])
                            } else {
                                let alertView = SCLAlertView()
                                alertView.showError("Sorry :(", subTitle: "This username has already been taken.")
                            }
                        })
                    } else {
                        let alertView = SCLAlertView()
                        alertView.showError("Sorry :(", subTitle: "Your name can't be blank!")
                    }
                }
            }
            alert.showCustom("Username", subTitle: "Please pick a user name!", color: UIColor.black, icon: SCLAlertViewStyleKit.imageOfEdit)
        }
    })
}

这是我的viewDidLoad

override func viewDidLoad() {
        self.view.addSubview(self.mapViewController.view)
        self.view.addSubview(self.tableController.view)
        print("View did load")          
        uid = (FIRAuth.auth()?.currentUser?.uid)!
        locatiOnsRef= FIRDatabase.database().reference(withPath: "/users/").child("\(uid)").child("locations")
        initialSetUp()
    }

我收到的输出看起来像这样

View did load
initially set up
observing event
user does not have username(or user does have username if I use a different account)
observing event
user does not have username(or user does have username if I use a different account)

我的Firebase数据结构:

以下是打印快照时发生的情况

observing event
Snap (FJpA8PGCmwPRT9xjdrZENMIH8wJ3) {
    email = "test@gmail.com";
    id = 10207417529265514;
    name = "Jason";
}

如果需要,我很乐意提供更多信息,但我认为它可能是函数中的内容.