This is what I try to do in code:
for i in 1...1000000000 {
print(i)
self.title = "\(i)"
}
on console it prints everything, but I can't see any updates in my navigation bar. Why?
Actually you could have a look at CADisplayLink which basically is a timer that is synchronized with the refresh of the display. At its most basic form it would be something like this:
func createDisplayLink() {
let displaylink = CADisplayLink(target: self, selector: #selector(step))
displaylink.add(to: .current, forMode: .defaultRunLoopMode)
}
#objc func step(displaylink: CADisplayLink) {
// Do the updates
}
Note: Please note that step will be called a lot, essentially on each screen update, which is 60-120 fps on current devices.
Related
I am facing one strange issue.
So I have created instance and allocated like below
var displayLink:CADisplayLink?
private func setupDisplayLink () {
self.displayLink = CADisplayLink(target: self, selector: #selector(displayLinkDidFire(link:)))
self.displayLink?.preferredFramesPerSecond = 30
self.displayLink?.add(to: .main, forMode: .common)
}
Now to remove display link I have from this Answer
self.displayLink?.remove(from: .main, forMode: .common) // comment this line and view controller correctly deallocated
self.displayLink?.invalidate()
because of line self.displayLink?.remove(from: .main, forMode: .common) my deinit method not called of view controller
In memory graph I am not able to identify the real problem. I was lucky that I have tried to comment that line and it works
Why that so ?
Stop displayLink like this:
displayLink?.invalidate()
displayLink = nil
I'm learning how to create a Pomodoro app, and am able to send notifications. However, I am totally clueless as to how to allow my timer label to update itself on reloading the app. Which means the timer works only when the app is open and not when it's in the foreground/background. Hoping to find a tutorial to learn from or just a quick answer code. Thanks!
Edit: Just to clear some misunderstandings, my app's Notification works fine with the timer, for example if 30mins is selected, the app would notify the user after 30mins. However, the problem is that when the app reopens, it resumes for example 29:57 seconds left on the timer label while the 30mins should have passed already.
*Added in AppDelegate*
var seconds = 0 //Timer countdown seconds
var currentDate = NSDate()
var setDate: Int = 0
func pauseApp(){
viewC.timer.invalidate() //invalidate timer
UserDefaults.standard.set(seconds, forKey: "current") //error occurs here where "Cannot assign value of type NSDate to type Timer"
setDate = UserDefaults.standard.integer(forKey: "current")
}
func startApp(){
let difference = currentDate.timeIntervalSince(NSDate() as Date) as Double
seconds = Int(Double(setDate) - difference)
viewC.updateTimer()
}
What someone suggests from a different thread is cancel the timer and store a NSDate when the app goes to the background. He stated we can use this notification to detect the app going to the background:
NSNotificationCenter.defaultCenter().addObserver(self, selector: "pauseApp", name: UIApplicationDidEnterBackgroundNotification, object: nil)
Then cancel the timer and store the date:
func pauseApp(){
self.stop() //invalidate timer
self.currentBackgroundDate = NSDate()
}
Use this notification to detect the user coming back:
NSNotificationCenter.defaultCenter().addObserver(self, selector: "startApp", name: UIApplicationDidBecomeActiveNotification, object: nil)
Then calculate the difference from the stored date to the current date, update your counter and start the timer again:
func startApp(){
let difference = self.currentBackgroundDate.timeIntervalSinceDate(NSDate())
self.handler(difference) //update difference
self.start() //start timer }
However, I do not fully understand this code (namely, the difference between the "handler" and my own "seconds") as am new to programming... Hoping for an answer or helpful insight.
Solved: I managed to solve it myself from this video https://www.youtube.com/watch?v=V6ta24iBNBQ
Using this concept of timeDifference as well as UserDefaults.standard.set....
I managed to adapt it to my personal app with the code
You can call Timer to run the timmer when the view loads.
var runTimer : Timer?
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
runTimer = Timer.scheduledTimer(timeInterval: 3, target: self, selector: #selector(myFun), userInfo: nil, repeats: true)
}
func myFun(){
//do your logic
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
runTimer?.invalidate()
}
How can I run a function every minute?
In JavaScript I can do something like setInterval, does something similar exist in Swift?
Wanted output:
Hello World once a minute...
var helloWorldTimer = NSTimer.scheduledTimerWithTimeInterval(60.0, target: self, selector: Selector("sayHello"), userInfo: nil, repeats: true)
func sayHello()
{
NSLog("hello World")
}
Remember to import Foundation.
Swift 4:
var helloWorldTimer = Timer.scheduledTimer(timeInterval: 60.0, target: self, selector: #selector(ViewController.sayHello), userInfo: nil, repeats: true)
#objc func sayHello()
{
NSLog("hello World")
}
If targeting iOS version 10 and greater, you can use the block-based rendition of Timer, which simplifies the potential strong reference cycles, e.g.:
weak var timer: Timer?
func startTimer() {
timer?.invalidate() // just in case you had existing `Timer`, `invalidate` it before we lose our reference to it
timer = Timer.scheduledTimer(withTimeInterval: 60.0, repeats: true) { [weak self] _ in
// do something here
}
}
func stopTimer() {
timer?.invalidate()
}
// if appropriate, make sure to stop your timer in `deinit`
deinit {
stopTimer()
}
While Timer is generally best, for the sake of completeness, I should note that you can also use dispatch timer, which is useful for scheduling timers on background threads. With dispatch timers, since they're block-based, it avoids some of the strong reference cycle challenges with the old target/selector pattern of Timer, as long as you use weak references.
So:
var timer: DispatchSourceTimer?
func startTimer() {
let queue = DispatchQueue(label: "com.domain.app.timer") // you can also use `DispatchQueue.main`, if you want
timer = DispatchSource.makeTimerSource(queue: queue)
timer!.schedule(deadline: .now(), repeating: .seconds(60))
timer!.setEventHandler { [weak self] in
// do whatever you want here
}
timer!.resume()
}
func stopTimer() {
timer = nil
}
For more information, see the the Creating a Timer section of Dispatch Source Examples in the Dispatch Sources section of the Concurrency Programming Guide.
For Swift 2, see previous revision of this answer.
If you can allow for some time drift here's a simple solution executing some code every minute:
private func executeRepeatedly() {
// put your code here
DispatchQueue.main.asyncAfter(deadline: .now() + 60.0) { [weak self] in
self?.executeRepeatedly()
}
}
Just run executeRepeatedly() once and it'll be executed every minute. The execution stops when the owning object (self) is released. You also can use a flag to indicate that the execution must stop.
Here's an update to the NSTimer answer, for Swift 3 (in which NSTimer was renamed to Timer) using a closure rather than a named function:
var timer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true) {
(_) in
print("Hello world")
}
You can use Timer (swift 3)
var timer = Timer.scheduledTimerWithTimeInterval(60, target: self, selector: Selector("function"), userInfo: nil, repeats: true)
In selector() you put in your function name
In swift 3.0 the GCD got refactored:
let timer : DispatchSourceTimer = DispatchSource.makeTimerSource(flags: [], queue: DispatchQueue.main)
timer.scheduleRepeating(deadline: .now(), interval: .seconds(60))
timer.setEventHandler
{
NSLog("Hello World")
}
timer.resume()
This is specially useful for when you need to dispatch on a particular Queue. Also, if you're planning on using this for user interface updating, I suggest looking into CADisplayLink as it's synchronized with the GPU refresh rate.
Here is another version algrid's answer with an easy way to stop it
#objc func executeRepeatedly() {
print("--Do something on repeat--")
perform(#selector(executeRepeatedly), with: nil, afterDelay: 60.0)
}
Here's an example of how to start it and stop it:
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
executeRepeatedly() // start it
}
override func viewWillDisappear(_ animated: Bool) {
super.viewWillDisappear(animated)
NSObject.cancelPreviousPerformRequests(withTarget: self) // stop it
}
timer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true, block: myMethod)
func myMethod(_:Timer) {
...
}
or
timer = Timer.scheduledTimer(withTimeInterval: 60, repeats: true) { _ in
...
}
make sure to invalid the timer at some point like your time is no longer visible, or you object is deist
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")
}
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)
}
Timer methods with a selector are supposed to have one parameter: The timer itself. Thus your code should really look like this: 1
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)
1: 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".
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
}
}
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.
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 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
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.
Swift3
var timer = Timer()
timer = Timer.scheduledTimer(timeInterval: 5, target: self, selector: #selector(self.compruebaConexion), userInfo: nil, repeats: true)
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)
}
I am trying to use the NSTimer to increment the progress bar in my app when recording voice (see the screenshot)
let timedClock = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("Counting:"), userInfo: nil, repeats: true)
internal func Counting(timer: NSTimer!) {
if timeCount == 0 {
//self.timedClock = nil
stopRecording(self) //performs segue to another view controller
} else {
timeCount--;
self.timer.text = "\(timeCount)"
}
print("counting called!")
progressBar.progress += 0.2
}
The progress bar works only for the first time after I compile and run the project. When the recording is finished, the app performs segue to another view controller to play the recorded audio. However, when I go back to the view for recording, the timer/progress bar automatically runs. I suspect the NSTimer object is still alive on the NSRunLoop. So I was wondering how to prevent the NSTimer from automatically running.
Inspired by the answer in this SO thread, I tried the following, but the NSTimer still automatically runs.
let timedClock = NSTimer(timeInterval: 1, target: self, selector: "Counting:", userInfo: nil, repeats: true)
NSRunLoop.currentRunLoop().addTimer(timedClock, forMode: NSRunLoopCommonModes)
This happens because when your controller created it's properties are automatically initialized. According to Apple Docs (and method's name) scheduledTimerWithTimeInterval create and return scheduled timer. So if you only want create your timer and call it by trigger function use it like this:
class MyClass {
var timer: NSTimer?
...
func enableTimer() {
timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: Selector("Counting:"), userInfo: nil, repeats: true)
}
func disableTimer() {
timer?.invalidate()
timer = nil
}
...
}
Sorry for the quick self-answer, as I just found out that I can use the invalidate() method to prevent the timer from automatically firing:
timedClock.invalidate()
Hope it helps someone in the future!