Example of fetching messages from Parse

gistfile1.swift

class ViewController: UITableViewController {
    var messages:[Message]?
    var timer:NSTimer?

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

    override func viewDidAppear(animated: Bool) {
        super.viewDidAppear(animated)
        self.refreshFired(nil)
        timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: "refreshFired:", userInfo: nil, repeats: true)
    }

    func refreshFired(sender:AnyObject?){
        let query = Message.query()
        query.orderByDescending("createdAt")
        query.includeKey("user")
        if let newestMessage = self.messages?.first {
            query.whereKey("createdAt", greaterThan: newestMessage.createdAt)
        }
        query.findObjectsInBackgroundWithBlock { (objects, errorOrNil) -> Void in
            if let error = errorOrNil {
                NSLog("Error fetching objects: \(error)")
                return
            }
            if let messagesFromAPI = objects as [Message]!{
                NSLog("Messages: \(messagesFromAPI)")
                dispatch_async(dispatch_get_main_queue(), { () -> Void in
                    let difference = messagesFromAPI.count
                    NSLog("New messages: \(difference)")
                    self.tableView.beginUpdates()
                    var indexPaths:[NSIndexPath] = Array()
                    for var i = 0; i < difference; i++ {
                        indexPaths.append(NSIndexPath(forRow: i, inSection: 0))
                    }
                    self.messages = messagesFromAPI + (self.messages ?? Array())
                    self.tableView.insertRowsAtIndexPaths(indexPaths, withRowAnimation: UITableViewRowAnimation.Automatic)
                    self.tableView.endUpdates()
                    self.tableView.reloadData()
                })
            }
        }
    }

    override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCellWithIdentifier("messageCell") as MessageCell
        let message = self.messages![indexPath.row]
        cell.messageBodyLabel.text = message.text
        return cell
    }

    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return messages?.count ?? 0
    }

}

class MessageCell: UITableViewCell {
    @IBOutlet weak var messageBodyLabel: UILabel!
}

class Message: PFObject, PFSubclassing {

    @NSManaged var text:String?
    @NSManaged var user:PFUser?

    class func parseClassName() -> String {
        return "Message"
    }

    override class func load() {
        self.registerSubclass()
    }
}