NSTimer doesn't get fired repeatedly in my Swift code - swift

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.

Related

Make Timer start counting as soon as ViewDidLoad is called

I have set Timer in ViewDidLoad in this way:
let timer = Timer.scheduledTimer(
timeInterval: 3, target: self, selector: #selector(handleAnimation),
userInfo: nil, repeats: true)
But until it fires out the first handleAnimation method I need to wait for 3 seconds.
Is there a way to make timer fire out the function as soon as the viewDidLoad function is executed?

Tell the timer fo fire immediately.
let timer = Timer.scheduledTimer(
timeInterval: 3, target: self, selector: #selector(handleAnimation),
userInfo: nil, repeats: true)
timer.fire()

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)

scheduledTimer not firing if I navigate to two viewcontrollers

I have a weak scheduledTimer:
weak var timer = Timer.scheduledTimer(timerInterval: 2.0, target: self, selector: #selector(fire), userInfo: ["id",id], repeats: false)
If I begin this timer and navigate to only one viewController, it will fire in the background with no issue. However, if I navigate to a second viewController before the timer fires, it will never go off. Any idea why this is happening?

To define
class viewController: UIViewController
{
var timer = Timer()
use in other function
func one()
{
timer = Timer.scheduledTimer(timeInterval: 2.0, target: self, selector: #selector(backClick), userInfo: ["id"], repeats: false)
}
func two()
{
timer = Timer.scheduledTimer(timeInterval: 2.0, target: self, selector: #selector(backClick), userInfo: ["id"], repeats: false)
}
inValidate() timer
override func viewDidDisappear(_ animated: Bool) {
super.viewDidDisappear(animated)
timer.fire()
}

Because of that was weak like #Alexandr Kolesnik 's comment, or may be you invalidated when first one is disappeared.

Swift: How to invalidate a timer if the timer starts from a function?

I have a timer variable in a function like this:
timer = NSTimer()
func whatever() {
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "timerbuiltingo", userInfo: nil, repeats: true)
}
when I try to stop the timer in the resulting timerbuiltingo function like this:
func timerbuiltingo() {
timer.invalidate()
self.timer.invalidate()
}
It doesn't stop it. How should I be doing this?

If you need to be able to stop the timer at any point in time, make it an instance variable.
If you will only ever need to stop it in the method it is called, you can have that method accept an NSTimer argument. The timer calling the method will pass itself in.
class ClassWithTimer {
var timer = NSTimer()
func startTimer() {
self.timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "timerTick:", userInfo: nil, repeats: true)
}
#objc func timerTick(timer: NSTimer) {
println("timer has ticked")
}
}
With this set up, we can now either call self.timer.invalidate() or, within timerTick, we can call timer.invalidate() (which refers to the timer which called the method).

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)