Error: Unrecognised Selector when using class reference - ios

Question

I have a class in a swift file called cloud I use a reference to that class in my project to call two of its methods. But I get the following error and the app crashes;
NSForwarding: warning: object 0x7fc938717160 of class 'App.Cloud' does
not implement methodSignatureForSelector: -- trouble ahead
Unrecognized selector -[App.Cloud persistentStoreWillChange]
(lldb)
Does anybody know who i could resolve this and why this is occurring ?
PS: The error only appears when installing the app and launching for the first time. If I quit and relaunch it does not appear, however it does not execute the methods.
Heres my class,
class Cloud {
let moc = (UIApplication.sharedApplication().delegate as! AppDelegate).managedObjectContext
func persistentStoreWillChange (notification:NSNotification) {
self.moc!.performBlock { () -> Void in
if self.moc!.hasChanges {
var error:NSError? = nil
self.moc!.save(&error)
if error != nil {
println("Save error: \(error)")
} else{
// drop any manged object refrences
self.moc!.reset()
}
}
}
}
func persistentStoreDidChange () {
println("Store Did Change")
}
//Refresh Data
func recieveChanges (notification:NSNotification){
self.moc!.performBlock { () -> Void in
self.moc!.mergeChangesFromContextDidSaveNotification(notification)
}
}
//View Will Appear
func addObsevers() {
NSNotificationCenter.defaultCenter().addObserver(self, selector: "persistentStoreDidChange:", name: NSPersistentStoreCoordinatorStoresDidChangeNotification, object: nil)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("persistentStoreWillChange:"), name:NSPersistentStoreCoordinatorStoresWillChangeNotification, object: moc!.persistentStoreCoordinator)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("recieveICloudChanges:"), name:NSPersistentStoreDidImportUbiquitousContentChangesNotification, object: moc!.persistentStoreCoordinator)
}
//View Will Dissapear
func removeObservers() {
NSNotificationCenter.defaultCenter().removeObserver(self, name: NSPersistentStoreCoordinatorStoresDidChangeNotification, object: nil)
NSNotificationCenter.defaultCenter().removeObserver(self, name: NSPersistentStoreCoordinatorStoresWillChangeNotification, object: moc!.persistentStoreCoordinator)
NSNotificationCenter.defaultCenter().removeObserver(self, name: NSPersistentStoreDidImportUbiquitousContentChangesNotification, object: moc!.persistentStoreCoordinator)
}
}
Class reference in View Controller:
let iCloudSync = Cloud()
override func viewWillAppear(animated: Bool) {
iCloudSync.addObsevers()
loadData()
}
override func viewWillDisappear(animated: Bool) {
iCloudSync.removeObservers()
}

Answer 1

You need to derive class Cloud from NSObject when you declare it, like this:
class Cloud : NSObject {
Otherwise your selectors are invisible to Objective-C.

Answer 2

You changed code but you forgot to change method declaration from
func persistentStoreDidChange () {
println("Store Did Change")
}
to
func persistentStoreDidChange (notification: NSNotification) {
println("Store Did Change")
}

Answer 3

Well you do this, which says to call persistentStoreDidChange on self when the notification triggers:
NSNotificationCenter.defaultCenter().addObserver(self,
selector: "persistentStoreDidChange",
name: NSPersistentStoreCoordinatorStoresDidChangeNotification,
object: nil)
But then it looks like you don't implement persistentStoreDidChange within class Cloud.
So either remove that observer, or implement the method.

Answer 4

Your methods have parameters so you must express this with ':' in their names. Changed code should look like this:
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("persistentStoreWillChange:"), name: NSPersistentStoreCoordinatorStoresWillChangeNotification, object: moc!.persistentStoreCoordinator)
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("recieveICloudChanges:"), name: NSPersistentStoreDidImportUbiquitousContentChangesNotification, object: moc!.persistentStoreCoordinator)