Scala：在带有嵌套Map的Map上使用toMap失败(Scala: using toMap on a Map with a nested Map fails)

 您必须记住， observeSingleEvent是异步触发的，因此将它放入Dispatch组可能是个好主意。 
 
 我建议你做的是从一个组内执行loadAllDataFromServerAboutGame方法，并且在完成触发之前不做任何事情，并且所有数据都已写入变量。 
 
 你在哪里调用loadAllDataFromServerAboutGame 
 
let group = DispatchGroup()
group.enter()
loadAllDataFromServerAboutGame()

group.notify(queue: .main, execute: {
    // Do something
}
 
 你的loadAllDataFromServerAboutGame方法： 
 
func loadAllDataFromServerAboutGame(){

    ref.child("\(gamePIN)").observeSingleEvent(of: .value, with: { (snapshot) in
        // Get user value
        let value = snapshot.value as? NSDictionary
        self.player1Name = value?["player1Name"] as? String ?? ""
        self.player2Name = value?["player2Name"] as? String ?? ""
        self.player3Name = value?["player3Name"] as? String ?? ""
        self.player4Name = value?["player4Name"] as? String ?? ""
        self.player5Name = value?["player5Name"] as? String ?? ""
        self.player6Name = value?["player6Name"] as? String ?? ""

        self.playerAmountBeforeTextChanging = value?["numberOfPlayers"] as? String ?? ""

        self.player1UID = value?["player1UID"] as? String ?? ""
        self.player2UID = value?["player2UID"] as? String ?? ""
        self.player3UID = value?["player3UID"] as? String ?? ""
        self.player4UID = value?["player4UID"] as? String ?? ""
        self.player5UID = value?["player5UID"] as? String ?? ""
        self.player6UID = value?["player6UID"] as? String ?? ""

        if let myNumber = NumberFormatter().number(from: self.playerAmountBeforeTextChanging) {
            self.numberOFPLayers = myNumber.intValue
        } else {
            print("Error converting text into 'int' value!")
        }

        print("Transcription: \(self.numberOFPLayers)")
        print("Player 3 Name: \(self.player3Name)")
        //HERE:
        group.leave()

        // ...
    }) { (error) in
        print("DataBase ERROR:\(error.localizedDescription)")
        //HERE:
        group.leave()
    }
}

You have to remember that the observeSingleEventis fired asynchronous, and therefore it might be a good idea to put it into a Dispatch Group. 
 
What I would suggest you do, is the to execute the method loadAllDataFromServerAboutGame from within a group, and not do anything until after it has finished firing, and all data has been written to the variables. 
 
Where you call loadAllDataFromServerAboutGame
 
let group = DispatchGroup()
group.enter()
loadAllDataFromServerAboutGame()

group.notify(queue: .main, execute: {
    // Do something
}
 
Your loadAllDataFromServerAboutGame method:
 
func loadAllDataFromServerAboutGame(){

    ref.child("\(gamePIN)").observeSingleEvent(of: .value, with: { (snapshot) in
        // Get user value
        let value = snapshot.value as? NSDictionary
        self.player1Name = value?["player1Name"] as? String ?? ""
        self.player2Name = value?["player2Name"] as? String ?? ""
        self.player3Name = value?["player3Name"] as? String ?? ""
        self.player4Name = value?["player4Name"] as? String ?? ""
        self.player5Name = value?["player5Name"] as? String ?? ""
        self.player6Name = value?["player6Name"] as? String ?? ""

        self.playerAmountBeforeTextChanging = value?["numberOfPlayers"] as? String ?? ""

        self.player1UID = value?["player1UID"] as? String ?? ""
        self.player2UID = value?["player2UID"] as? String ?? ""
        self.player3UID = value?["player3UID"] as? String ?? ""
        self.player4UID = value?["player4UID"] as? String ?? ""
        self.player5UID = value?["player5UID"] as? String ?? ""
        self.player6UID = value?["player6UID"] as? String ?? ""

        if let myNumber = NumberFormatter().number(from: self.playerAmountBeforeTextChanging) {
            self.numberOFPLayers = myNumber.intValue
        } else {
            print("Error converting text into 'int' value!")
        }

        print("Transcription: \(self.numberOFPLayers)")
        print("Player 3 Name: \(self.player3Name)")
        //HERE:
        group.leave()

        // ...
    }) { (error) in
        print("DataBase ERROR:\(error.localizedDescription)")
        //HERE:
        group.leave()
    }
}