When is a Cocoa binding 'set'

Question

I've got an NSArrayController set in my storyboard where I set the mode to Entity Name with a name of Client, and bound the managed object context, selection indexes, and sort descriptors. My NSPopupButton links to that array controller and when I run I see all the elements I expect on the button.

Now I made a strong @IBOutlet in my code and I'm trying to access the contents:

let objs = clientArrayController.arrangedObjects as! [Client]
print("I have \(objs.count) clients")

I tried that code in viewDidLoad, viewWillAppear and viewDidAppear. They all say 0 clients. Clearly that's not possible as I have the clients showing in the UI.

What am I doing wrong here?

Answer 1

viewDidLoad, viewWillAppear, and viewDidAppear are possibly all called before your array controller collects its data from the core data store - hence they (correctly) report a count of zero. To get word of any changes to your array controller's arrangedObjects array you could use one of the aforementioned methods to install an observer that watches this object and reports any changes:

// MyPopUpController.swift

var ArrayControllerArrangedObjectsObservationContext = "arrayController.arrangedObjects"


func viewDidLoad() {
    arrayController.addObserver(self, 
        forKeyPath: "arrangedObjects", 
        options: .New | .Old, 
        context: &ArrayControllerArrangedObjectsObservationContext)
}

You're given the opportunity to respond to changes in observeValueForKeyPath...

// MyPopUpController.swift

override func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
    switch context {
        case &ArrayControllerArrangedObjectsObservationContext:
            // Check counts here
        default:
            super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)
}

If you only need the observer on start-up, after you've checked the counts, and done whatever you need to do you should then remove the observer:

// MyPopUpController.swift

arrayController.removeObserver(self, 
    forKeyPath: "arrangedObjects", 
    context: &ArrayControllerArrangedObjectsObservationContext)