ios - 返回 1 个屏幕时，应用程序在加载 Firebase 数据之前崩溃

Question

在实际加载数据之前检索数据并离开 View Controller 时，我的 Firebase 功能遇到了一个小问题。我意识到，如果我在实际数据加载到 VC 之前按下 Controller 中的后退按钮，我的控制台就会崩溃，这是 *** 由于未捕获的异常“InvalidPathValidation”而终止应用程序，原因:“(child:) 必须是非空字符串且不包含“.” '#' '$' '[' 或 ']''。仅当我尝试退出得太快，以防用户在加载数据之前想要去其他地方时，才会发生这种情况，否则每个功能都可以正常工作。

我已经在 viewDidDissapear 中删除了两个 Firebase 函数的观察者，这会有所帮助，因为您不想让观察者保持打开状态，但这并不能解决我的崩溃问题。我还有一个进度平视显示器，一旦加载数据就会显示并关闭，但没有成功。例如，下面是我的 Firebase 函数之一，用于检索数据。

func retrieveMessages() {
        let ref = Database.database().reference().child("locations").child(titleString)
        ref.observe(.childAdded) { (snapshot) in
            if snapshot.exists() {
                let snapshotValue = snapshot.value as! Dictionary<String,String>
                let text = snapshotValue["message"]!
                let sender = snapshotValue["username"]!
                let img = snapshotValue["userImage"]!
                let upvote = snapshotValue["upvote"]!
                let timestamp = snapshotValue["timestamp"]!
                let message = ChatMessage()
                message.msgTimestamp = timestamp
                message.messageBody = text
                message.sender = sender
                message.chatImageURL = img
                let upvoteInt = Int(upvote)
                message.upvoteString = upvoteInt!
                self.chatMessageArray.append(message)
                self.chatTable.reloadData()
                self.chatRoomScrollToBottom(animated: true)
                        }
                    }
                }

我的下一个假设是禁用后退按钮，直到数据完全加载？这可以解决这个问题，但我想知道如果我立即按下后退按钮，是否有办法停止此功能或我触发的任何 FB 功能？感谢任何帮助。

Answer 1

也许您可以尝试运行以下命令，并对输出进行注释:

import UIKit
import Firebase

class FirebaseTableViewController: UITableViewController  {

    lazy var ref: DatabaseReference = Database.database().reference()
    var chatMessageArray: Array<ChatMessage> = []
    var messageRef: DatabaseReference!
    var titleString = ""    //TODO: Update this
    var chatTable: UITableView = UITableView() //TODO: Update this



    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        print(titleString) // TODO: Check that it dose not contain: '.' '#' '$' '[' or ']''
        messageRef = ref.child("locations").child(titleString)
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        chatMessageArray.removeAll()
        messageRef.observe(.childAdded) { (snapshot) in
            self.createMessage(snapshot:snapshot)
        }
    }

    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)

        // removeAllObservers: Removes all observers at the current reference, but does not remove any observers at child references
        messageRef.removeAllObservers()
    }

    func chatRoomScrollToBottom(animated: Bool) {

    }

    func createMessage(snapshot: DataSnapshot) {
        guard let snapshotValue = snapshot.value as? Dictionary<String,String> else {
            print("Error with snapshotValue")
            return
        }
        guard let text = snapshotValue["message"],
            let sender = snapshotValue["username"],
            let img = snapshotValue["userImage"],
            let upvote = snapshotValue["upvote"],
            let timestamp = snapshotValue["timestamp"] else {
                print("Error with snapshotValue[''] values")
                return
        }
        let message = ChatMessage()
        message.msgTimestamp = timestamp
        message.messageBody = text
        message.sender = sender
        message.chatImageURL = img
        guard let upvoteInt = Int(upvote) else {
            print ("Error with pvoteInt")
            return
        }
        message.upvoteString = String(upvoteInt)
        self.chatMessageArray.append(message)
        self.chatTable.reloadData()
        self.chatRoomScrollToBottom(animated: true)
    }

}

希望对您有所帮助!