ios - 不正确的 Firebase 数据返回

Question

我有以下 Swift 和 Firebase 代码，它按预期(最初)返回数据，但如果数据被另一个用户更改并且当前用户返回到表中，它会显示旧数据。它只会在用户离开并返回到显示正确数据的表中时更新新数据。

就好像数据被缓存了，但我禁用了持久化):

import UIKit
import Firebase

class Agent_NewRequests: UITableViewController {

    let custom = custom()
    var dbConnector = FIRDatabase.database().reference()

    var userID:String!
    var searchResults = [agentNewRequests]()
    var requestID:String!

    var loadingOverlay = LoadingOverlay()


    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func viewWillAppear(animated: Bool) {
        self.searchResults.removeAll(keepCapacity: false)
        FIRAuth.auth()!.addAuthStateDidChangeListener() { (auth, user) in
            if user != nil {
                // user authenticated
                self.userID = user!.uid
                self.retrieveRequests()
            } else {
                // No user is signed in
                self.custom.showLogin(self.self)
            }
        }
    }

    override func viewWillDisappear(animated: Bool) {
        dbConnector.removeAllObservers()
    }

    func retrieveRequests() {
        if self.userID == "" {
            loadingOverlay.hideOverlayView()
            // todo - show error
            return
        }

        loadingOverlay.showOverlay(self.view)
        var timeLastUpdated = ""
        self.searchResults.removeAll(keepCapacity: false)

        let userRef = dbConnector.child("requests/\(self.userID)")
        userRef.queryEqualToValue("Submitted", childKey: "status")
        userRef.observeSingleEventOfType(.ChildAdded, withBlock: { snapshot in
            guard snapshot.exists() else {
                // No data found, handle error otherwise will crash
                self.checkTable()
                self.loadingOverlay.hideOverlayView()
                return
            }

            if let _:String = snapshot.value!["status"] as? String { } else {
                self.checkTable()
                self.loadingOverlay.hideOverlayView()
                return
            }

            let status = snapshot.value!["status"] as! String

            if status != "Submitted" {
                self.checkTable()
                return
            }

            let key = snapshot.key as String
            let tenantID = snapshot.value!["tenant_id"] as! String
            let address = snapshot.value!["address"] as! String
            let desc = snapshot.value!["description"] as! String
            let timeUpdate:Int = snapshot.value!["time_updated"] as! Int
            let priority = snapshot.value!["priority"] as! Int

            let dateFormat = NSDateFormatter()
            dateFormat.dateStyle = NSDateFormatterStyle.LongStyle
            dateFormat.timeStyle = NSDateFormatterStyle.ShortStyle

            if timeUpdate == 0 { // if it has never been updated, use time created instead for lastupdated
                let cTimeInterval = snapshot.value!["time_created"] as? NSTimeInterval
                let updateTime = NSDate(timeIntervalSince1970: cTimeInterval! / 1000)
                timeLastUpdated = dateFormat.stringFromDate(updateTime)
            } else {
                let uTimeInterval = snapshot.value!["time_updated"] as? NSTimeInterval
                let updateTime = NSDate(timeIntervalSince1970: uTimeInterval! / 1000)
                timeLastUpdated = dateFormat.stringFromDate(updateTime)

            }
            var imgData:String = ""

            self.searchResults += [agentNewRequests(requestID: key, tenantID: tenantID, address: address, description: desc, lastUpdated: timeLastUpdated, mediaData: mediaData, priority: priority)]
            dispatch_async(dispatch_get_main_queue()){
                self.checkTable()
            }
        }) { error in
            print(error.description)
            self.loadingOverlay.hideOverlayView()
        }
    }


    func checkTable() {
        if (self.searchResults.count > 0) {
            self.searchResults = self.searchResults.reverse()
            self.tableView.reloadData()
            self.loadingOverlay.hideOverlayView()
            // remove any previous signs of errorMessageLabel
            self.tableView.backgroundView = nil
            self.tableView.separatorColor = custom.UIColorFromRGB(0x574987, alphaValue: 1)
            self.tableView.separatorStyle = UITableViewCellSeparatorStyle.SingleLine
        } else {
            self.tableView.reloadData()
            self.loadingOverlay.hideOverlayView()
            // Display a message that the table is empty
            let errorMessageLabel = UILabel()
            errorMessageLabel.frame = CGRectMake(0, 0, self.tableView.bounds.width, (self.tableView.bounds.height + 100))
            errorMessageLabel.text = "No new requests found"
            errorMessageLabel.numberOfLines = 1
            errorMessageLabel.textColor = UIColor.blackColor()
            errorMessageLabel.textAlignment = NSTextAlignment.Center
            errorMessageLabel.sizeToFit()
            self.tableView.backgroundView = errorMessageLabel
            self.tableView.separatorColor = UIColor.clearColor()
            self.tableView.separatorStyle = UITableViewCellSeparatorStyle.SingleLine
        }
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {

        let cell:Agent_NewRequests_Cell = self.tableView.dequeueReusableCellWithIdentifier("requestCell")
            as! Agent_NewRequests_Cell
        cell.idLabel.text = searchResults[indexPath.row].description
        cell.updatedLabel.text = searchResults[indexPath.row].lastUpdated
        cell.addressLabel.text = searchResults[indexPath.row].address

        return cell
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return searchResults.count
    }

    override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
        requestID = searchResults[indexPath.row].requestID
        self.performSegueWithIdentifier("newToRequestCard", sender: indexPath);
    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject!) {
        if (segue.identifier == "newToRequestCard") {
            let requestCard = segue.destinationViewController as! Agent_Request_Card;
            requestCard.toPass_requestID = self.requestID
            requestCard.toPass_agentID = self.userID
        }
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
    }
}

如果我将它从 .ObserveSingleEventOfType 更改为 .ObserveEventType 它会按预期工作但是...如果数据在其他地方被删除并且没有其他数据，则 UI 只是等待更新而我不希望这样，我需要通过 UI 更新告知用户没有数据(这永远不会发生)

Answer 1

使用 ObserveEventType 而不是 ObserveSingleEventOfType 并只检查数据是否存在。如果不是，请使用消息更新 UI。如果是，则照常继续。