Timer, #selector explanation - swift

I need a timer so I used this code:
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(generalKnowledge.method), userInfo: nil, repeats: true)
But I do not understand the #selector. I tried multiple times but it doesn't work.


selector() is where you'd add in the function that you want it to call every timeInterval you set. In your example it's every second.
Do bare in mind that in Swift 4 and above, you need to add #objc before a function if you want to call it in a selector like so:
#objc func handleEverySecond() {
print("Hello world!")
}
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(handleEverySecond), userInfo: nil, repeats: true)


A selector is essentially a message that is sent to an object. It was mostly used in objective-C and Swift has tried to move away from it. However, there are still some objective-C APIs that use it, including the timer one.
This is why selectors must be marked as #objc since it needs to be exposed in order to be seen.
So when you pass a selector to the timer, you're telling it to send this message to the class when it fires.
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(action), userInfo: nil, repeats: true)
#objc func action() {
print("timer fired")
}
Also, it's important to remember that you need to keep a reference to the timer outside of the scope of the function.

Related

Swift timer method terminates the app early with SIGABRT error

Below is my code for having a timer change a variable from 0 to 1, which results in a SIGABRT error when the timer tries to fire:
var timerToggle = 0
let timer = Timer.scheduledTimer(timeInterval: 5.0, target: self, selector: #selector(fireTimer), userInfo: nil, repeats: false)
#objc func fireTimer() {
timerToggle = 1
}
I know others who've had this problem seem to solve it by placing the timer declaration within the override func viewDidLoad() function but whenever I do that it gives me the following error
"Initialization of immutable value 'timer' was never used; consider replacing with assignment to '_' or removing it."
Any help would be greatly appreciated

"Initialization of immutable value 'timer' was never used; consider
replacing with assignment to '_' or removing it."
This is just a warning not an error. You can still go ahead and initialise timer in viewDidLoad.

If it is needed to activate once-fired timer in viewDidLoad, it should look somehow like the following
class MyController: UIViewController {
var timerToggle = 0
private var timer: Timer?
deinit {
timer?.invalidate()
}
#objc func fireTimer() {
timerToggle = 1
timer = nil
}
override func viewDidLoad() {
super.viewDidLoad()
timer = Timer.scheduledTimer(timeInterval: 5.0, target: self,
selector: #selector(fireTimer), userInfo: nil, repeats: false)
}
}

If you are not going to access the timer anymore simply add below to viewDidLoad
_ = Timer.scheduledTimer(timeInterval: 5.0,
target: self,
selector: #selector(fireTimer),
userInfo: nil,
repeats: false)

ScheduledTimer selector. Objective-c or Swift? [duplicate]

I tried
var timer = NSTimer()
timer(timeInterval: 0.01, target: self, selector: update, userInfo: nil, repeats: false)
But, I got an error saying
'(timeInterval: $T1, target: ViewController, selector: () -> (), userInfo: NilType, repeats: Bool) -> $T6' is not identical to 'NSTimer'

This will work:
override func viewDidLoad() {
super.viewDidLoad()
// Swift block syntax (iOS 10+)
let timer = Timer(timeInterval: 0.4, repeats: true) { _ in print("Done!") }
// Swift >=3 selector syntax
let timer = Timer.scheduledTimer(timeInterval: 0.4, target: self, selector: #selector(self.update), userInfo: nil, repeats: true)
// Swift 2.2 selector syntax
let timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: #selector(MyClass.update), userInfo: nil, repeats: true)
// Swift <2.2 selector syntax
let timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: "update", userInfo: nil, repeats: true)
}
// must be internal or public.
#objc func update() {
// Something cool
}
For Swift 4, the method of which you want to get the selector must be exposed to Objective-C, thus #objc attribute must be added to the method declaration.

Repeated event
You can use a timer to do an action multiple times, as seen in the following example. The timer calls a method to update a label every half second.
Here is the code for that:
import UIKit
class ViewController: UIViewController {
var counter = 0
var timer = Timer()
#IBOutlet weak var label: UILabel!
// start timer
#IBAction func startTimerButtonTapped(sender: UIButton) {
timer.invalidate() // just in case this button is tapped multiple times
// start the timer
timer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(timerAction), userInfo: nil, repeats: true)
}
// stop timer
#IBAction func cancelTimerButtonTapped(sender: UIButton) {
timer.invalidate()
}
// called every time interval from the timer
func timerAction() {
counter += 1
label.text = "\(counter)"
}
}
Delayed event
You can also use a timer to schedule a one time event for some time in the future. The main difference from the above example is that you use repeats: false instead of true.
timer = Timer.scheduledTimer(timeInterval: 2.0, target: self, selector: #selector(delayedAction), userInfo: nil, repeats: false)
The above example calls a method named delayedAction two seconds after the timer is set. It is not repeated, but you can still call timer.invalidate() if you need to cancel the event before it ever happens.
Notes
If there is any chance of starting your timer instance multiple times, be sure that you invalidate the old timer instance first. Otherwise you lose the reference to the timer and you can't stop it anymore. (see this Q&A)
Don't use timers when they aren't needed. See the timers section of the Energy Efficiency Guide for iOS Apps.
Related
How to work with dates and time in Swift

Updated to Swift 4, leveraging userInfo:
class TimerSample {
var timer: Timer?
func startTimer() {
timer = Timer.scheduledTimer(timeInterval: 5.0,
target: self,
selector: #selector(eventWith(timer:)),
userInfo: [ "foo" : "bar" ],
repeats: true)
}
// Timer expects #objc selector
#objc func eventWith(timer: Timer!) {
let info = timer.userInfo as Any
print(info)
}
}

As of iOS 10 there is also a new block based Timer factory method which is cleaner than using the selector:
_ = Timer.scheduledTimer(withTimeInterval: 5, repeats: false) { timer in
label.isHidden = true
}

Swift 5
I personally prefer the Timer with the block closure:
Timer.scheduledTimer(withTimeInterval: 1, repeats: false) { (_) in
// TODO: - whatever you want
}

Swift 3, pre iOS 10
func schedule() {
DispatchQueue.main.async {
self.timer = Timer.scheduledTimer(timeInterval: 20, target: self,
selector: #selector(self.timerDidFire(timer:)), userInfo: nil, repeats: false)
}
}
#objc private func timerDidFire(timer: Timer) {
print(timer)
}
Swift 3, iOS 10+
DispatchQueue.main.async {
self.timer = Timer.scheduledTimer(withTimeInterval: 20, repeats: false) { timer in
print(timer)
}
}
Notes
It needs to be on the main queue
Callback function can be public, private, ...
Callback function needs to be #objc

Check with:
Swift 2
var timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: Selector("update"), userInfo: nil, repeats: true)
Swift 3, 4, 5
var timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(self.update), userInfo: nil, repeats: true)

You will need to use Timer instead of NSTimer in Swift 3.
Here is an example:
Timer.scheduledTimer(timeInterval: 1,
target: self,
selector: #selector(YourController.update),
userInfo: nil,
repeats: true)
// #objc selector expected for Timer
#objc func update() {
// do what should happen when timer triggers an event
}

First declare your timer
var timer: Timer?
Then add line in viewDidLoad() or in any function you want to start the timer
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(action), userInfo: nil, repeats: false)
This is the func you will callback it to do something it must be #objc
#objc func action () {
print("done")
}

for swift 3 and Xcode 8.2
(nice to have blocks, but if You compile for iOS9 AND want userInfo):
...
self.timer = Timer(fireAt: fire,
interval: deltaT,
target: self,
selector: #selector(timerCallBack(timer:)),
userInfo: ["custom":"data"],
repeats: true)
RunLoop.main.add(self.timer!, forMode: RunLoopMode.commonModes)
self.timer!.fire()
}
func timerCallBack(timer: Timer!){
let info = timer.userInfo
print(info)
}

SimpleTimer (Swift 3.1)
Why?
This is a simple timer class in swift that enables you to:
Local scoped timer
Chainable
One liners
Use regular callbacks
Usage:
SimpleTimer(interval: 3,repeats: true){print("tick")}.start()//Ticks every 3 secs
Code:
class SimpleTimer {/*<--was named Timer, but since swift 3, NSTimer is now Timer*/
typealias Tick = ()->Void
var timer:Timer?
var interval:TimeInterval /*in seconds*/
var repeats:Bool
var tick:Tick
init( interval:TimeInterval, repeats:Bool = false, onTick:#escaping Tick){
self.interval = interval
self.repeats = repeats
self.tick = onTick
}
func start(){
timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector: #selector(update), userInfo: nil, repeats: true)//swift 3 upgrade
}
func stop(){
if(timer != nil){timer!.invalidate()}
}
/**
* This method must be in the public or scope
*/
#objc func update() {
tick()
}
}

timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(createEnemy), userInfo: nil, repeats: true)
And Create Fun By The Name createEnemy
fund createEnemy ()
{
do anything ////
}

In Swift 3 something like this with #objc:
func startTimerForResendingCode() {
let timerIntervalForResendingCode = TimeInterval(60)
Timer.scheduledTimer(timeInterval: timerIntervalForResendingCode,
target: self,
selector: #selector(timerEndedUp),
userInfo: nil,
repeats: false)
}
#objc func timerEndedUp() {
output?.timerHasFinishedAndCodeMayBeResended()
}

If you init method of timer
let timer = Timer(timeInterval: 3, target: self, selector: #selector(update(_:)), userInfo: [key : value], repeats: false)
func update(_ timer : Timer) {
}
then add it to loop using method other selector will not be called
RunLoop.main.add(timer!, forMode: .defaultRunLoopMode)
NOTE : If you are want this to repeat make repeats true and keep the reference of timer otherwise update method will not be called.
If you are using this method.
Timer.scheduledTimer(timeInterval: seconds, target: self, selector: #selector(update(_:)), userInfo: nil, repeats: true)
keep a reference for later use if repeats is true.

I tried to do in a NSObject Class and this worked for me:
DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(300)) {
print("Bang!") }

NSTimer has been renamed to Timer in Swift 4.2.
this syntax will work in 4.2:
let timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(UIMenuController.update), userInfo: nil, repeats: true)

does not implement methodSignatureForSelector: Unrecognized selector (NSTimer)

I am using an NSTimer in my Swift app in the following way:
func playEvent(eventIndex : Int){
if (eventIndex < 2){
let currEvent = self.eventArray[eventIndex]
currEvent?.startEvent()
let nextIndex = eventIndex + 1
NSTimer.scheduledTimerWithTimeInterval((currEvent?.duration)!, target: self, selector: "playEvent(nextIndex)", userInfo: nil, repeats: true)
}
else if (eventIndex==2){
self.eventArray[eventIndex]?.startEvent()
NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: "finishSentence", userInfo: nil, repeats: true)
}
else{
//do nothing
}
}
I think the problem may be either that I am not property calling the selector method with a parameter. If that is impossible, how could I work around this?
There is being called on the first NSTimer instance. Here is the full Swift class for reference: https://gist.github.com/ebbnormal/79941733b82f5fe58282

You can't pass nextIndex into a selector directly. One option for NSTimer could be to pass values via userInfo, for example:
NSTimer.scheduledTimerWithTimeInterval(1, target: self,
selector: "mySelector:",
userInfo: NSNumber(integer: 999),
repeats: true)
func mySelector(timer: NSTimer){
print(timer.userInfo)
}

A selector is represented by the method name
func playEvent()
selector: "playEvent"
If the method has one parameter, a colon is added
func playEvent(eventIndex : Int)
selector: "playEvent:"
If the method has multiple parameters, all parameter names are concatenated separated by colons
func playEvent(eventIndex : Int, flag: Bool)
selector: "playEvent:flag:"
Using NSTimer the direct parameter is designated to hold the timer instance.
func playEvent(timer : NSTimer)
You have to pass further parameters via the userInfo object of the timer.

NSTimer doesn't get fired repeatedly in my Swift code

I scheduled a timer in my viewDidAppear: method, but it just fire once and never fire again, the code is just like below
override func viewDidAppear(animated: Bool) {
super.viewDidAppear(animated)
timer = NSTimer(timeInterval: 1, target: self, selector: "test", userInfo: nil, repeats: true)
timer.fire()
}
func test() {
print("timer test")
}

Actually, you didn't schedule it. Try this:
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("test"), userInfo: nil, repeats: true)
And get rid of timer.fire().
Be aware that if you create a timer in viewDidAppear then a new timer will be created every time your view appears.

Calling a method after a fixed period of time in swift [duplicate]

I tried
var timer = NSTimer()
timer(timeInterval: 0.01, target: self, selector: update, userInfo: nil, repeats: false)
But, I got an error saying
'(timeInterval: $T1, target: ViewController, selector: () -> (), userInfo: NilType, repeats: Bool) -> $T6' is not identical to 'NSTimer'

This will work:
override func viewDidLoad() {
super.viewDidLoad()
// Swift block syntax (iOS 10+)
let timer = Timer(timeInterval: 0.4, repeats: true) { _ in print("Done!") }
// Swift >=3 selector syntax
let timer = Timer.scheduledTimer(timeInterval: 0.4, target: self, selector: #selector(self.update), userInfo: nil, repeats: true)
// Swift 2.2 selector syntax
let timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: #selector(MyClass.update), userInfo: nil, repeats: true)
// Swift <2.2 selector syntax
let timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: "update", userInfo: nil, repeats: true)
}
// must be internal or public.
#objc func update() {
// Something cool
}
For Swift 4, the method of which you want to get the selector must be exposed to Objective-C, thus #objc attribute must be added to the method declaration.

Repeated event
You can use a timer to do an action multiple times, as seen in the following example. The timer calls a method to update a label every half second.
Here is the code for that:
import UIKit
class ViewController: UIViewController {
var counter = 0
var timer = Timer()
#IBOutlet weak var label: UILabel!
// start timer
#IBAction func startTimerButtonTapped(sender: UIButton) {
timer.invalidate() // just in case this button is tapped multiple times
// start the timer
timer = Timer.scheduledTimer(timeInterval: 0.5, target: self, selector: #selector(timerAction), userInfo: nil, repeats: true)
}
// stop timer
#IBAction func cancelTimerButtonTapped(sender: UIButton) {
timer.invalidate()
}
// called every time interval from the timer
func timerAction() {
counter += 1
label.text = "\(counter)"
}
}
Delayed event
You can also use a timer to schedule a one time event for some time in the future. The main difference from the above example is that you use repeats: false instead of true.
timer = Timer.scheduledTimer(timeInterval: 2.0, target: self, selector: #selector(delayedAction), userInfo: nil, repeats: false)
The above example calls a method named delayedAction two seconds after the timer is set. It is not repeated, but you can still call timer.invalidate() if you need to cancel the event before it ever happens.
Notes
If there is any chance of starting your timer instance multiple times, be sure that you invalidate the old timer instance first. Otherwise you lose the reference to the timer and you can't stop it anymore. (see this Q&A)
Don't use timers when they aren't needed. See the timers section of the Energy Efficiency Guide for iOS Apps.
Related
How to work with dates and time in Swift

Updated to Swift 4, leveraging userInfo:
class TimerSample {
var timer: Timer?
func startTimer() {
timer = Timer.scheduledTimer(timeInterval: 5.0,
target: self,
selector: #selector(eventWith(timer:)),
userInfo: [ "foo" : "bar" ],
repeats: true)
}
// Timer expects #objc selector
#objc func eventWith(timer: Timer!) {
let info = timer.userInfo as Any
print(info)
}
}

As of iOS 10 there is also a new block based Timer factory method which is cleaner than using the selector:
_ = Timer.scheduledTimer(withTimeInterval: 5, repeats: false) { timer in
label.isHidden = true
}

Swift 5
I personally prefer the Timer with the block closure:
Timer.scheduledTimer(withTimeInterval: 1, repeats: false) { (_) in
// TODO: - whatever you want
}

Swift 3, pre iOS 10
func schedule() {
DispatchQueue.main.async {
self.timer = Timer.scheduledTimer(timeInterval: 20, target: self,
selector: #selector(self.timerDidFire(timer:)), userInfo: nil, repeats: false)
}
}
#objc private func timerDidFire(timer: Timer) {
print(timer)
}
Swift 3, iOS 10+
DispatchQueue.main.async {
self.timer = Timer.scheduledTimer(withTimeInterval: 20, repeats: false) { timer in
print(timer)
}
}
Notes
It needs to be on the main queue
Callback function can be public, private, ...
Callback function needs to be #objc

Check with:
Swift 2
var timer = NSTimer.scheduledTimerWithTimeInterval(0.01, target: self, selector: Selector("update"), userInfo: nil, repeats: true)
Swift 3, 4, 5
var timer = Timer.scheduledTimer(timeInterval: 0.01, target: self, selector: #selector(self.update), userInfo: nil, repeats: true)

You will need to use Timer instead of NSTimer in Swift 3.
Here is an example:
Timer.scheduledTimer(timeInterval: 1,
target: self,
selector: #selector(YourController.update),
userInfo: nil,
repeats: true)
// #objc selector expected for Timer
#objc func update() {
// do what should happen when timer triggers an event
}

First declare your timer
var timer: Timer?
Then add line in viewDidLoad() or in any function you want to start the timer
timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(action), userInfo: nil, repeats: false)
This is the func you will callback it to do something it must be #objc
#objc func action () {
print("done")
}

for swift 3 and Xcode 8.2
(nice to have blocks, but if You compile for iOS9 AND want userInfo):
...
self.timer = Timer(fireAt: fire,
interval: deltaT,
target: self,
selector: #selector(timerCallBack(timer:)),
userInfo: ["custom":"data"],
repeats: true)
RunLoop.main.add(self.timer!, forMode: RunLoopMode.commonModes)
self.timer!.fire()
}
func timerCallBack(timer: Timer!){
let info = timer.userInfo
print(info)
}

SimpleTimer (Swift 3.1)
Why?
This is a simple timer class in swift that enables you to:
Local scoped timer
Chainable
One liners
Use regular callbacks
Usage:
SimpleTimer(interval: 3,repeats: true){print("tick")}.start()//Ticks every 3 secs
Code:
class SimpleTimer {/*<--was named Timer, but since swift 3, NSTimer is now Timer*/
typealias Tick = ()->Void
var timer:Timer?
var interval:TimeInterval /*in seconds*/
var repeats:Bool
var tick:Tick
init( interval:TimeInterval, repeats:Bool = false, onTick:#escaping Tick){
self.interval = interval
self.repeats = repeats
self.tick = onTick
}
func start(){
timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector: #selector(update), userInfo: nil, repeats: true)//swift 3 upgrade
}
func stop(){
if(timer != nil){timer!.invalidate()}
}
/**
* This method must be in the public or scope
*/
#objc func update() {
tick()
}
}

timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(createEnemy), userInfo: nil, repeats: true)
And Create Fun By The Name createEnemy
fund createEnemy ()
{
do anything ////
}

In Swift 3 something like this with #objc:
func startTimerForResendingCode() {
let timerIntervalForResendingCode = TimeInterval(60)
Timer.scheduledTimer(timeInterval: timerIntervalForResendingCode,
target: self,
selector: #selector(timerEndedUp),
userInfo: nil,
repeats: false)
}
#objc func timerEndedUp() {
output?.timerHasFinishedAndCodeMayBeResended()
}

If you init method of timer
let timer = Timer(timeInterval: 3, target: self, selector: #selector(update(_:)), userInfo: [key : value], repeats: false)
func update(_ timer : Timer) {
}
then add it to loop using method other selector will not be called
RunLoop.main.add(timer!, forMode: .defaultRunLoopMode)
NOTE : If you are want this to repeat make repeats true and keep the reference of timer otherwise update method will not be called.
If you are using this method.
Timer.scheduledTimer(timeInterval: seconds, target: self, selector: #selector(update(_:)), userInfo: nil, repeats: true)
keep a reference for later use if repeats is true.

I tried to do in a NSObject Class and this worked for me:
DispatchQueue.main.asyncAfter(deadline: .now() + .milliseconds(300)) {
print("Bang!") }

NSTimer has been renamed to Timer in Swift 4.2.
this syntax will work in 4.2:
let timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(UIMenuController.update), userInfo: nil, repeats: true)