Timer does not run in Swift 3.0 playground

Question

Working in playground with Swift 3.0 I have this code:

struct Test {
    func run() {
        var timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: false) { timer in
            print("pop")
        }
    }
}

let test = Test()
test.run()

But nothing is printing to console. I've read How can I use NSTimer in Swift? and most of the usage of timer that I've seen in answers and tutorials online involves a selector so I tried this:

class Test {
    func run() {
        var timer = Timer.scheduledTimer(timeInterval: 0.4, target: self, selector: #selector(self.peep), userInfo: nil, repeats: false)
    }

    @objc func peep() {
        print("peep")
    }
}

let test = Test()
test.run()

Still nothing seems to print to console. If I add timer.fire(), then I get the console prints, but obviously that defeats the purpose. What do I need to change to get the timer to run?

EDIT:

So adding CFRunLoopRun() after I called the run method for my Test struct did the trick. Much Thanks to those who answered, especially @AkshayYaduvanshi (who's comment pointed me to CFRunLoopRun()) and @JoshCaswell (whose answer brought up the fact that I timer only works with a run loop).

Check this [link](http://stackoverflow.com/questions/29232334/using-nstimer-in-swift-playground) — , Oct 14 '16 at 19:41

score 25 · Answer 1 · edited Sep 30 '17 at 19:06

Your first version works if you allow the Playground to run indefinitely via PlaygroundSupport:

import Foundation
import PlaygroundSupport

PlaygroundPage.current.needsIndefiniteExecution = true 

let timer = Timer.scheduledTimer(withTimeInterval: 3, repeats: true) { timer in
  print("Timer Fired at: \(timer.fireDate)")
}

Adding a run loop manually also works, and might be needed sometimes, but in your case this simple instruction is enough to make the Timer work properly.

score 8 · Accepted Answer · answered Oct 14 '16 at 19:41

8

You need to start a run loop.

RunLoop.main.run(until: Date(timeIntervalSinceNow: 3))

The timer doesn't do anything unless there is a working run loop accepting input. The program simply ends.

Timer reference:

Timers work in conjunction with run loops. [...] it fires only when one of the run loop modes to which the timer has been added is running and able to check if the timer’s firing time has passed.

answered Oct 14 '16 at 19:41

jscs

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Thanks for the rapid response. I missed that in the reference, I have to do some reading and testing before I can be sure, but this seems like the problem cause I'm not using runloops at all. – Mercutio Oct 14 '16 at 19:51

Timer does not run in Swift 3.0 playground

2 Answers2