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Why can't I cancel a local notification in my iOS app?(in Swift)

Prelude

I have mentioned the fact that I am working on my first iOS app in a number of my previous posts and as such I face a number of newbie/noob(?) problems. They are not really problems as much as they are simply things that I do not know, for e.g. the following,

Thankfully, I have managed to make at least one generic solution and contribute it to the community i.e. my open-source Xcode project template(HTML5StarterAppWithSwift) which you can get from Github.

So this post basically describes another very simple problem that I have found a solution to, but I do not fully understand why the problem was occurring in the first place.

Introduction

As I have mentioned in this post, my iOS app uses local notifications i.e. UILocalNotification and in my app a certain chain of events can cause the local notifications to be cancelled. Sounds fairly straight forward right? Well it is and it is not, read on to find out exactly what I mean

My problem

Now if you look at UIApplication, there are two methods to cancel notifications, below is a description of these from the Apple Docs
  1. cancelAllLocalNotifications: Cancels the delivery of all scheduled local notifications.
  2. cancelLocalNotification: Cancels the delivery of the specified scheduled local notification.

How was I trying to cancel the notifications?

Local notifications are divided into certain categories in my app and local notifications in iOS can bring an app to the foreground, which is where the notification category comes into play. How? you see, when my app is brought to the foreground, the following method in the AppDelegate is invoked
func application(application: UIApplication, didReceiveLocalNotification notification: UILocalNotification)
and when that happens the category of the notification that brought the app to the foreground is determined and all the notifications in that category are cancelled.

As I have identified before, there are 2 methods to cancel local notifications, now if I just used the cancelAllNotifications method, in the AppDelegate as follows, 
func application(application: UIApplication, didReceiveLocalNotification notification: UILocalNotification) {
    application.cancelAllLocalNotifications()    
}
that would work i.e. all the notifications would be cancelled. However I only wanted to cancel notifications of a particular category and not all of them so if I tried to cancel a single notification by doing something like this,
func application(application: UIApplication, didReceiveLocalNotification notification: UILocalNotification) {
    let dict = notification.userInfo!
    let notificationType = dict["type"] as! Int
    let notificationTypeX = 99
    if notificationType == notificationTypeX {
        //cancel all notifications of type X
        for notification:AnyObject in UIApplication.sharedApplication().scheduledLocalNotifications {
            let localNotification = notification as! UILocalNotification
            let lnDict = notification.userInfo!
            let type = lnDict["type"] as! Int
            if type == notificationType {
                application.cancelLocalNotification(localNotification)

            }
        }
    }
}
then it would not work i.e. the individual notifications that I wanted to cancel would not be cancelled. Why? As I said earlier, I do not fully understand why this is happening, however I did find a fix to my problem.

How did I solve my problem?

So in my app,  I have a helper classes(something like Helper.swift in the project), so if I move the above logic into the helper class then I am able to cancel individual notifications via the above logic. So a function/method like this would work
func cancelNotification(category:Int) {
    let application = UIApplication.sharedApplication()
    for notification:AnyObject in application.scheduledLocalNotifications {
        let scheduledNoti = notification as! UILocalNotification
        if let type = scheduledNoti.userInfo?["type"] as? Int {
            if type == category {
               application.cancelLocalNotification(scheduledNoti)
            }
        }
    }
}
Again, I do not know exactly why this is i.e. why can't you cancel a single notification from the AppDelegate? The only reason, I have not made a big effort to research into finding out why this is happening is because I have a ton of other problems to solve and get my app ready for release. Making an app Icon? ahh, I have no idea where to even start for that (Fiver maybe?) Anyway, if you are reading this blog and know more than I do, then please leave a comment.
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