How to Check If a Nstimer Is Running or Not in Swift

How to check if a NSTimer is running or not in Swift?

What I do (in both languages) is to make my timer weak. In swift it would be a weak optional.

weak var myTimer: NSTimer?

Then I create a timer with

myTimer = NSTimer.scheduledTimerWithTimeInterval(1,
          target: self,
          selector: "timerFired:",
          userInfo: nil,
          repeats: false)

And then you can use

if timer == nil

to tell if it's running.

To stop the timer you just call

myTimer?.invalidate()

In Objective-C it would be

[myTimer invalidate];

That works in Objective-C because sending messages to nil pointers is valid, and just does nothing.

If you don't want to use a weak optional, you can query a timer to see if it's running by looking at it's valid property.

Check if Timer is running

I recommend to use self-checking startTimer() and stopTimer() functions, the timer will be started only if it's not currently running, the stop function sets the timer variable reliably to nil.

var timer : Timer?

func startTimer()
{
    if timer == nil {
        timer = Timer.scheduledTimer...
    }
}

func stopTimer()
{
    if timer != nil {
       timer!.invalidate()
       timer = nil
    }
}

Swift how to check if timer is done using time from certain variable?

There's an easier way to do this, using a single timer which you use to update a display, and just keep track of whether you are running or walking - something like this

@IBAction func cmdStartStopAction(_ sender: Any)
{
    durationTimerDisplay = 0.1 // this will update the display every 0.1 seconds
    currentlyRunning = true // assume we start by running

    if timerDisplay == nil // this means we are starting the timer
    {
        durationRun = Double(txtTimerRun.text!)!    // assumes you have a text box to enter the times
        durationWalk = Double(txtTimerWalk.text!)!

        durationRemaining = durationRun             // we can use this to display a countdown timer

        // start the display update timer
        timerDisplay = Timer.scheduledTimer(timeInterval: durationTimerDisplay, target: self, selector: #selector(onTimerDisplay), userInfo: nil, repeats: true)
    }
    else
    {
        timerDisplay.invalidate()
        timerDisplay = nil
    }
}

@objc func onTimerDisplay()
{
    durationRemaining -= durationTimerDisplay       // count down timer
    if durationRemaining <= 0                       // switch between running and walking when you reach zero
    {
        // switch from running to walking, or walking to running
        currentlyRunning = !currentlyRunning
        if currentlyRunning {
            durationRemaining = durationRun
        }
        else {
            durationRemaining = durationWalk
        }
    }

    // create a display using a label lblTimer
    if currentlyRunning {
        lblTimer.text = String(format: "RUN: %.1f", durationRemaining)
    }
    else {
        lblTimer.text = String(format: "WALK: %.1f", durationRemaining)
    }
}

How to find if NSTimer is active or not?

When a non repeating timer fires it marks itself as invalid so you can check whether it is still valid before cancelling it (and of course then ridding yourself of it).

if ( [timer isValid] && yourOtherCondition){
    [timer invalidate], timer=nil;
}

In your case you have a repeating timer so it will always be valid until you take some action to invalidate it. Looks like in this case you are running a countdown so it will be up to you to make sure you invalidate and rid yourself of it when the countdown reaches the desired value (In your updateCountdown method)

swift 3 check if timer running

This is expected. You are assigning the new Timer instance to weak var inside your function, which will cause it to be deallocated when you exit function scope. The function's timer variable must be declared as inout

func startTimer(timer: inout Timer?, interval: Double, _selector: Selector, _repeats: Bool) {
if (timer == nil){
        timer = Timer.scheduledTimer(timeInterval: interval, target: self, selector: _selector, userInfo: nil, repeats: _repeats)
    }

The same goes for your second function - you are assigning nil only to local variable inside function scope, not to the variable outside.

iOS - check if Timer is valid or not

In your code, instead of using timer.isValid, how about change to timer != nil, like following,

if result != nil {
    timer.invalidate()
//        timer = Timer.scheduledTimer(timeInterval:2, target: self, selector: #selector(ViewController.noResults), userInfo: nil, repeats:false)
}

if timer != nil { // here
    print("has not been 2 seconds yet")
} else {
    print("do some action")
}

Hope this help!

How to check if NSTimer has been already invalidated

Once you invalidate the timer, simply call release on it (assuming you've retained the reference you're holding on to) and then nil out your reference. That way when you exit the view, trying to invalidate the timer a second time will just call that method on nil instead, which does nothing.

Alternatively, you can use -[NSTimer isValid] to check if it's valid before invalidating, but there's really no reason to hold onto your reference after invalidating it the first time anyway. Also, if your real problem is that you haven't retained your reference and so the first -invalidate actually leaves you with a reference pointing at a released object, then calling -isValid won't help anyway.

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