Unrecognized selector sent to class when using NSTimer in Swift; NSInvalidArgumentException

Question

I'm trying to use an NSTimer to run a function at a certain interval, but every time it runs the program crashes with an exception:

+[Project.Class updateLabel]: unrecognized selector sent to class... Terminating app due to uncaught exception "NSInvalidArgumentException".

The code is as follows:

class SecondViewController: UIViewController { // MARK: Properties override func viewDidLoad() { super.viewDidLoad() do { try updateLabel() try startTimer() } catch{ self.showAlert() } } @IBOutlet weak var i2cLabel: UILabel! // MARK: Actions func startTimer() throws { _ = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: Selector("updateLabel"), userInfo: nil, repeats: true) } func showAlert() { } func updateLabel() throws { } }

If I comment out the NSTimer line, the program compiles and runs just fine.

Note that updateLabel(), the selector function, takes no arguments so calling it as a selector without a colon suffix should work. This seems to be unique to this problem.

Edited to explain how this problem in unique.

K. Standeven
– K. Standeven

2016-01-27 00:28:06 +00:00
Commented Jan 27, 2016 at 0:28 — K. Standeven
– K. Standeven, Commented Jan 27, 2016 at 0:28

Community · Accepted Answer · 2017-05-23 12:23:28Z

Try update your code to:

override func viewDidLoad() { super.viewDidLoad() do { updateLabel() try startTimer() } catch{ self.showAlert() } } // MARK: Actions func startTimer() throws { _ = NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: Selector("updateLabel"), userInfo: nil, repeats: true) } func showAlert() { } func updateLabel() { }

It seems that: NSTimer don't know call a function throws. So it will crash.

I have tried to find some official or some article describe about it. But sad that I can't find now.

You can reference to this question: Reference

Hope this help!

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