Call a function using NSTimer - ios

Question

So as the code shown below, the function loadView 3 is supposed to run 300 seconds(5 minutes) after the user tapped the button. But when I build and run, it does not. I also did a few experiments, I changed the timer to 5 seconds, it worked. So after the app is suspended from iOS system, the NSTimer doesn't run anymore? So what's the problem, how can I fix it?
#IBAction func buttonTapped(sender: AnyObject) {
NSTimer.scheduledTimerWithTimeInterval(300, target: self, selector: #selector(ViewController.loadView3), userInfo: nil, repeats: false)
createLocalNotification()
}
func createLocalNotification() {
let localnotification = UILocalNotification()
localnotification.fireDate = NSDate(timeIntervalSinceNow: 300)
localnotification.applicationIconBadgeNumber = 1
localnotification.soundName = UILocalNotificationDefaultSoundName
localnotification.alertBody = "Hello!"
UIApplication.sharedApplication().scheduleLocalNotification(localnotification)
}
func loadView3() {
label.text = "e89saa"
}

Answer 1

You could try something like this. The approach is, if timer works proceed with same logic, otherwise (probably app is killed or went to background), save firedDate and update UI before showing controller in method viewWillAppear.
#IBAction func buttonTapped(sender: AnyObject) {
NSTimer.scheduledTimerWithTimeInterval(300, target: self, selector: #selector(ViewController.loadView3), userInfo: nil, repeats: false)
createLocalNotification()
}
func createLocalNotification() {
let localnotification = UILocalNotification()
localnotification.fireDate = NSDate(timeIntervalSinceNow: 300)
localnotification.applicationIconBadgeNumber = 1
localnotification.soundName = UILocalNotificationDefaultSoundName
localnotification.alertBody = "Hello!"
UIApplication.sharedApplication().scheduleLocalNotification(localnotification)
// save in UserDefaults fireDate
let defaults = NSUserDefaults.standardUserDefaults()
defaults.setObject(localnotification.fireDate, forKey: "firedDate")
defaults.synchronize()
}
func loadView3() {
// reset in UserDefaults fireDate
let defaults = NSUserDefaults.standardUserDefaults()
defaults.removeObjectForKey("firedDate")
defaults.synchronize()
label.text = "e89saa"
}
override func viewWillAppear(animated: Bool) {
super.viewWillAppear(animated) // No need for semicolon
// retrieve fireDate from UserDefaults
let defaults = NSUserDefaults.standardUserDefaults()
let fireDate = defaults.objectForKey("firedData")
// check if we should update UI
if let _ = fireDate as? NSDate! {
if currentDate.compare(firedDate) == NSComparisonResult.OrderedDescending {
loadView3()
}
}
}