How to delay the return to the calling function swift - swift

Question

In my application the user can press a button. That in turn leads to a function call which is showed below:
In ViewController.Swift
#IBAction func pickMeUpButton(sender: AnyObject) {
sendPushNotificationController().sendPushNotification("sendRequest",userInfo: defaults.stringForKey("x73")!, userInf23: defaults.stringForKey("x23")! )
locationController.getLocationForShortTime() // --> here i want the timer to finish the 5 seconds before proceeding
activityIndicator.center = self.view.center
activityIndicator.startAnimating()
self.view.addSubview(activityIndicator)
//activityIndicator.stopAnimating()
}
And this is the class function where the call is being made to
In getUserLocation.swift
func initManager(){
locationManager = CLLocationManager()
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.requestAlwaysAuthorization()
locationManager.startUpdatingLocation()
}
func getLocationForShortTime(){
initManager()
timer = NSTimer.scheduledTimerWithTimeInterval(5, target: self, selector: "stopGettingLocation", userInfo: nil, repeats: false)
}
func stopGettingLocation(){
locationManager.stopUpdatingLocation()
}
So this will make the application get the users location for 5 seconds and then the timer will stop the updates. What i want to do is when the five seconds has elapsed and the location update stops THEN i would like the calling function to proceed to next line.
I though of some solutions using boolean, but it is not a nice solution. Im thinking there might be a better way to do this?

Answer 1

Others have told you what to do, but not why.
You need to adjust your thinking.
With an event-driven device like an iPhone/iPad, you can't stop processing on the main thread for 5 seconds. The UI would lock up, and after a couple of seconds the system would kill your app as being hung.
Instead, what you do is to invoke a block of code (a closure) after a delay.
You could rewrite your function like this:
#IBAction func pickMeUpButton(sender: AnyObject)
{
sendPushNotificationController().sendPushNotification("sendRequest",
userInfo: defaults.stringForKey("x73")!,
userInf23: defaults.stringForKey("x23")! )
initManager()
//Start the activity indicator during the delay
activityIndicator.center = self.view.center
self.view.addSubview(activityIndicator)
activityIndicator.startAnimating()
dispatch_after(
dispatch_time(DISPATCH_TIME_NOW, Int64(5.0 * Double(NSEC_PER_SEC))),
dispatch_get_main_queue())
{
//The code in the braces gets run after the delay value
locationManager.stopUpdatingLocation()
activityIndicator.stopAnimating()
}
//dispatch_after returns immediately, so code here will run before
//the delay period passes.
}
That button action code will:
Call initManager to start the location manager running.
Immediately create an activity indicator, add it to the view controller's content view, and start it spinning.
Then, the call to dispatch_after will wait for 5 seconds before running the code in the braces, which will stop the location manger and stop the activity indicator.

Answer 2

For delaying a function-call you can use dispatch_after. It's syntax is a little bit ugly so you can also use this delay function:
/// delays the execution of the passed function
func delay(delay: Double, closure: ()->()) {
dispatch_after(
dispatch_time(DISPATCH_TIME_NOW, Int64(delay * Double(NSEC_PER_SEC))),
dispatch_get_main_queue(),
closure)
}
// calling directly (locationManager gets captured; which is in this case negligible to consider)
delay(5.0, closure: locationManager.stopUpdatingLocation)
// or indirect through your function
delay(5.0, closure: stopGettingLocation)

Answer 3

Pass the closure to getLocationForShortTime. The one that should be run once the thing is finished. I can't really test the code, but it's probably something like:
class Handler { // <- This is the wrapper class for completion closures
private let run: Void -> Void
init(_ run: Void -> Void) { self.run = run }
}
lazy var locationManager: CLLocationManager! = self.lazyLocationManager()
func lazyLocationManager() -> CLLocationManager {
let _locationManager = CLLocationManager()
_locationManager.delegate = self
_locationManager.desiredAccuracy = kCLLocationAccuracyBest
_locationManager.requestAlwaysAuthorization()
return _locationManager
}
func getLocationQuick(onComplete: Void -> Void) { // <- This takes the closure
locationManager.startUpdatingLocation()
let timer = NSTimer.scheduledTimerWithTimeInterval(
5,
target: self,
selector: "gotLocationQuick:",
userInfo: Handler(onComplete), // <- Here you wrap the completion closure
repeats: false // and pass it to the timer
)
NSRunLoop.mainRunLoop().addTimer(timer, forMode: NSDefaultRunLoopMode)
}
func gotLocationQuick(timer: NSTimer) {
locationManager.stopUpdatingLocation()
let completionHandler = timer.userInfo as! Handler
completionHandler.run()
}
#IBAction func pickMeUpButton(sender: AnyObject) {
sendPushNotificationController().sendPushNotification(
"sendRequest",
userInfo: defaults.stringForKey("x73")!,
userInf23: defaults.stringForKey("x23")!
)
activityIndicator.center = self.view.center
self.view.addSubview(activityIndicator)
activityIndicator.startAnimating()
locationController.getLocationQuick() { // <- You post the request for
activityIndicator.stopAnimating() // geolocation and indicate the code
} // to be run once it's finished
}