Timer.scheduledTimer does not work in Swift 3

I want to call the method `func adjustmentBestSongBpmHeartRate()` every 1.1 second. I used Timer, but it doesn't work. I have read the document and found a lot of sample code, it still does work! Is there anything I missed?

timer = Timer.scheduledTimer(timeInterval: 1.1, target: self, selector: #selector(self.adjustmentBestSongBpmHeartRate), userInfo: nil, repeats: false)
timer.fire()

func adjustmentBestSongBpmHeartRate() {
print("frr")
}

Timer methods with a selector are supposed to have one parameter: The timer itself. Thus your code should really look like this: <sup>1</sup>

Timer.scheduledTimer(timeInterval: 1.1,
target: self,
selector: #selector(self.adjustmentBestSongBpmHeartRate(_:),
userInfo: nil,
repeats: false)

@objc func adjustmentBestSongBpmHeartRate(_ timer: Timer) {
print("frr")
}


Note that if your app only runs on iOS >= 10, you can use the new method that takes a block to invoke rather than a target/selector. Much cleaner and more type-safe:

class func scheduledTimer(withTimeInterval interval: TimeInterval,
repeats: Bool,
block: @escaping (Timer) -> Void) -> Timer

That code would look like this:


timer = Timer.scheduledTimer(withTimeInterval: 1.1,
repeats: false) {
timer in
//Put the code that be called by the timer here.
print("frr")
}

Note that if your timer block/closure needs access to instance variables from your class you have to take special care with `self`. Here's a good pattern for that sort of code:


timer = Timer.scheduledTimer(withTimeInterval: 1.1,
repeats: false) {

//"[weak self]" creates a "capture group" for timer
[weak self] timer in

//Add a guard statement to bail out of the timer code
//if the object has been freed.
guard let strongSelf = self else {
return
}
//Put the code that be called by the timer here.
print(strongSelf.someProperty)
strongSelf.someOtherProperty = someValue
}

## Edit (updated 15 December)

<sup>1</sup>: I should add that the method you use in the selector has to use Objective-C dynamic dispatch. In Swift 4 and later, the individual methods you reference must be tagged with the `@objc` tag. In previous versions of Swift you could also declare the entire class that defines the selector with the `@objc` qualifier, or you could make the class that defined the selector a subclass of `NSObject` or any class that inherits from `NSOBject`. (It's quite common to define the method the timer calls inside a `UIViewController`, which is a subclass of `NSObject`, so it used to "just work".

I found that creating the timer in an OperationQueue Operation did not work. I assume this is because there is no runloop.

Therefore, the following code fixed my problem:



DispatchQueue.main.async {
// timer needs a runloop?
self.timeoutTimer = Timer.scheduledTimer(timeInterval: self.timeout, target: self, selector: #selector(self.onTimeout(_:)), userInfo: nil, repeats: false)
}

Swift 5, Swift 4 Simple way only call with Dispatch Queue Async

DispatchQueue.main.async
{
self.andicator.stopAnimating()
self.bgv.isHidden = true

Timer.scheduledTimer(withTimeInterval: 1.0, repeats: false, block: { _ in

obj.showAlert(title: "Successfully!", message: "Video save successfully to Library directory.", viewController: self)

})
}

I found that if you try to initialize the timer directly at the class-level, it won't work if you're targeting a selector in that same class. When it fires, it can't find the selector.

To get around this, I only initialize the timer ***after*** the object containing the selector has been initialized. If it's in the same class, put the initialization code in the `ViewDidLoad` or similar. Just not in the initializer. Then it will work. No dispatch queue needed.

Also, you do *not* need to use a selector that accepts the timer as a parameter. You can, but contrary to the answer with a ton of votes, that's not actually true, or more specifically, it works fine for me without it, just as you have it without it.

By the way, I think the reason the dispatch queue worked is because you're forcing the timer to be created after the object was initializing, confirming my above statement.

let timer:Timer?

override func viewDidLoad(){
super.viewDidLoad()

timer = Timer.scheduledTimer(timeInterval: 1.1, target: self, selector: #selector(adjustmentBestSongBpmHeartRate), userInfo: nil, repeats: false)

timer.fire()

}

func adjustmentBestSongBpmHeartRate() {
print("frr")
}

Note: This is code typed from memory, not copied from Xcode so it may not compile, but hopefully you get the idea.

Try this -


if #available(iOS 10.0, *) {
self.timer = Timer.scheduledTimer(withTimeInterval: 0.2, repeats: false, block: { _ in
self.update()
})
} else {
self.timer = Timer.scheduledTimer(timeInterval: 0.2, target: self, selector: #selector(self.update), userInfo: nil, repeats: false)
}



Mostly the problem must have been because of iOS version of mobile.

my two cents.
I read about "didLoad" and when invoking it.
so we can use a delay:


class ViewController: UIViewController {

var timer: Timer?

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


final func killTimer(){
self.timer?.invalidate()
self.timer = nil
}


final private func startTimer() {

// make it re-entrant:
// if timer is running, kill it and start from scratch
self.killTimer()
let fire = Date().addingTimeInterval(1)
let deltaT : TimeInterval = 1.0

self.timer = Timer(fire: fire, interval: deltaT, repeats: true, block: { (t: Timer) in

print("hello")

})

RunLoop.main.add(self.timer!, forMode: RunLoopMode.commonModes)

}

**Swift3**

var timer = Timer()

timer = Timer.scheduledTimer(timeInterval: 5, target: self, selector: #selector(self.compruebaConexion), userInfo: nil, repeats: true)

**Swift 3**

In my case it worked after I added to my method the **@obj prefix**

Class TestClass {
private var timer: Timer?

func start() {
guard timer == nil else { return }
timer = Timer.scheduledTimer(timeInterval: 60, target: self, selector: #selector(handleMyFunction), userInfo: nil, repeats: false)
}

func stop() {
guard timer != nil else { return }
timer?.invalidate()
timer = nil
}


@objc func handleMyFunction() {
// Code here
}
}

I have solved the question asked by myself.
I'm using apple watch to control my iphone app.
I try to press a button on apple watch to present a new viewcontroller on iphone.

When I write Timer in `override func viewDidLoad()`, Timer doesn't work. I move Timer to `override func viewWillAppear()` it works.

I think maybe there's something wrong with controlling by apple watch

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