NSTimer

Parameters#

Parameter	Details
`interval`	The time, in seconds, to wait beforing firing the timer; or, in repeating timers, the time between firings.
`target`	The object to call the `selector` on
`selector`	In Swift, a `Selector` object specifying the method to call on the `target`
`repeats`	If `false`, fire the timer only once. If `true`, fire the timer every `interval` seconds.

Remarks#

An NSTimer allows you to send a message to a target after a specified period of time elapses.

Creating a Timer

This will create a timer to call the doSomething method on self in 5 seconds.

Swift

let timer = NSTimer.scheduledTimerWithTimeInterval(5,
                               target: self,
                             selector: Selector(doSomething()),
                             userInfo: nil,
                              repeats: false)

Swift 3

 let timer = Timer.scheduledTimer(timeInterval: 1,
                                        target: self, 
                                      selector: #selector(doSomething()), 
                                      userInfo: nil, 
                                       repeats: true)

Objective-C

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(doSomething) userInfo:nil repeats:NO];

Setting repeats to false/NO indicates that we want the timer to fire only once. If we set this to true/YES, it would fire every five seconds until manually invalidated.

Manually firing a timer

Swift

timer.fire()

Objective-C

[timer fire];

Calling the fire method causes an NSTimer to perform the task it would have usually performed on a schedule.

In a non-repeating timer, this will automatically invalidate the timer. That is, calling fire before the time interval is up will result in only one invocation.

In a repeating timer, this will simply invoke the action without interrupting the usual schedule.

Invalidating a timer

Swift

timer.invalidate()

Objective-C

[timer invalidate];

This will stop the timer from firing. Must be called from the thread the timer was created in, see Apple’s notes:

You must send this message from the thread on which the timer was installed. If you send this message from another thread, the input source associated with the timer may not be removed from its run loop, which could prevent the thread from exiting properly.

Notes: Once timer has been invalidated, its impossible to fire same invalidated timer.Instead you need to initialise the invalidated timer again and trigger fire method.

Timer frequency options

Repeated Timer event

Swift

class ViewController: UIViewController {
 
    var timer = NSTimer()
    
    override func viewDidLoad() {
        NSTimer.scheduledTimerWithTimeInterval(1.0, target: self, selector: Selector(self.timerMethod()), userInfo: nil, repeats: true)
    }

    func timerMethod() {
        print("Timer method called")
    }

    func endTimer() {
        timer.invalidate()
    }
}

Swift 3

class ViewController: UIViewController {
     
        var timer = Timer()
        
        override func viewDidLoad() {
            Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(self.timerMethod()), userInfo: nil, repeats: true)
        }
    
        func timerMethod() {
            print("Timer method called")
        }

        func endTimer() {
            timer.invalidate()
        }
    }

Must be invalidated manually if desired.

Swift

Non-repeated delayed Timer event

NSTimer.scheduledTimerWithTimeInterval(3.0, target: self, selector: Selector(self.timerMethod()), userInfo: nil, repeats: false)

Swift 3

 Timer.scheduledTimer(timeInterval: 3.0, target: self, selector: #selector(self.timerMethod()), userInfo: nil, repeats: false)

Timer will be fired once, 3 seconds after time of execution. Will be invalidated automatically, once fired.

Passing of data using Timer

If you you want to pass some data with the timer trigger you can do it with the userInfoparameter.

Here is the simple approach that gives brief idea about how you can pass the data to triggered method from the Timer.

[Swift 3]

Timer.scheduledTimer(timeInterval: 1.0, target: self, selector:#selector(iGotCall(sender:)), userInfo: ["Name": "i am iOS guy"], repeats:true)

[Objective - C]

NSTimer* timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                      target:self
                                                    selector:@selector(iGotCall:)
                                                    userInfo:@"i am iOS guy" repeats:YES];

The above line of code passing ["Name": "i am iOS guy"] into the userInfo. So now when the iGotCall get call you can get the passed value as below code snippet.

[Swift 3]

func iGotCall(sender: Timer) {
        print((sender.userInfo)!)
    }

[Objective - C]

- (void)iGotCall:(NSTimer*)theTimer {
    NSLog (@"%@", (NSString*)[theTimer userInfo]);
}