How to update UITableViewCells using NSTimer and NSNotificationCentre in Swift

Question

NOTE: Asking for answers in Swift please.

What I\'m trying to do:

• Have tableview cells update every 1 second and disp

Answer 1

It might be a solution not reloading cells at all. Just make the cells listen to an update notification and change their label accordingly. I assume you subclass UITableViewCell and give the cell a storedDate property. You will set that property when preparing the cell.

The timer will just fire the notification.

Remember to unregister the cell from notification center in dealloc

Here is a quick an dirty example.

The View Controller containing your TableView:

class ViewController: UIViewController, UITableViewDataSource {

    @IBOutlet weak var tableView: UITableView!

    var timer: NSTimer!


    //MARK: UI Updates

    func fireCellsUpdate() {
        let notification = NSNotification(name: "CustomCellUpdate", object: nil)
        NSNotificationCenter.defaultCenter().postNotification(notification)
    }

    //MARK: UITableView Data Source

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

    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return 10
    }

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        let cellIdentifier = "CustomCell"
        let cell = tableView.dequeueReusableCellWithIdentifier(cellIdentifier) as! CustomTableViewCell
        cell.timeInterval = 20
        return cell
    }

    //MARK: View Lifecycle
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        self.timer = NSTimer(timeInterval: 1.0, target: self, selector: Selector("fireCellsUpdate"), userInfo: nil, repeats: true)
        NSRunLoop.currentRunLoop().addTimer(self.timer, forMode: NSRunLoopCommonModes)
    }


    deinit {
        self.timer?.invalidate()
        self.timer = nil
    }

}

The custom cell subclass:

class CustomTableViewCell: UITableViewCell {

    @IBOutlet weak var label: UILabel!

    var timeInterval: NSTimeInterval = 0 {
        didSet {
            self.label.text = "\(timeInterval)"
        }
    }

    //MARK: UI Updates

    func updateUI() {
        if self.timeInterval > 0 {
            --self.timeInterval
        }
    }

    //MARK: Lifecycle

    override func awakeFromNib() {
        super.awakeFromNib()
        // Initialization code

        let notificationCenter = NSNotificationCenter.defaultCenter()
        notificationCenter.addObserver(self, selector: Selector("updateUI"), name: "CustomCellUpdate", object: nil)
    }

    deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

}

I'm pretty sure this example doesn't adhere to your app's logic. Just showing how things are glowed together.