NSTimer scheduledTimerWithTimeInterval - not calling funciton - ios

Question

I want to run a timer in the background. So I created a singleton.
The problem is that after the set 5.0 seconds, it does not call the function timeEnded(). Xcode proposes to add #Objc in front of the function (like this: #Objc func timeEnded() {...) to solve some problem (I don't get what, though). But it still doesn't call that function. Any ideas?
class TimerService {
static let instance = TimerService()
var internalTimer: NSTimer?
func startTimer() {
guard internalTimer != nil else {
return print("timer already started")
}
internalTimer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: #selector(TimerService.timeEnded), userInfo: nil, repeats: false)
}
func timeEnded() {
//NSNotificationCenter.defaultCenter().postNotificationName("timerEnded", object: nil)
print("timer Ended")
}
}

Answer 1

You never actually start the timer because your startTimer() function will always return before reaching the line of code where you create the timer.
In your guard statement you only continue the execution of the function if internalTimer != nil but the only place where you set the timer is after that statement. Thus, your timer is never created and internalTimer will always be nil.
This should fix your problem:
func startTimer() {
guard internalTimer == nil else {
return print("timer already started")
}
internalTimer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: #selector(TimerService.timeEnded), userInfo: nil, repeats: false)
}

Answer 2

Selectors are a feature of Objective-C and can only be used with methods that are exposed to the dynamic Obj-C runtime. You cannot have a selector to a pure Swift method.
If your class inherits from NSObject then its public methods are exposed to Obj-C automatically. Since your class does not inherit from NSObject you have to use the #objc attribute to indicate that you want this method exposed to Obj-C so that it may be called with an Obj-C selector.
#selector() is the new syntax in Swift 2.2. It allows the compiler to check that the selector you're trying to use actually exists. The old syntax is deprecated and will be removed in Swift 3.0.