Swift 2.0: Cannot invoke 'setValue' with an argument list of

Question

I am converting an app from Objective-C to Swift 2.0 and while converting an NSView-subclass, I am getting an error while trying to store a weak back-reference from a CALayer to the ActionViewItemInternal which is needed so that the layer drawing code can access the item data. I want to use a weak reference in order to avoid a retain-cycle (item object retains layer so layer needs a weak reference back to the item object).

class WeakReference {
    weak var reference: AnyObject?

    init(reference: AnyObject) {
        self.reference = reference
    }
}

class ActionView: NSView {

    // Used to store an item in ActionView.items
    private class ActionViewItemInternal {
        var actionViewItem: ActionViewItem
        var layer: CALayer
        ...

        init(withItem actionViewItem: ActionViewItem) {
            self.actionViewItem = actionViewItem
            let layer = CALayer()
            // !!!!!!!!!!!!!!!!!!!!!!!!!!
            // other init and error here:
            // !!!!!!!!!!!!!!!!!!!!!!!!!!
            layer.setValue(value: WeakReference(reference: self), forKey: "ActionViewItem")
            self.layer = layer
        }

    }

    var items: [ActionViewItem] = [ActionViewItem]()
    ...
}

Where ActionItemView is defined as:

@objc protocol ActionViewItem {
    var name: String { get set }
    var icon: NSImage { get set }
    var enabled: Bool { get set }
}

I am getting the error:

ActionView.swift:73:19: Cannot invoke 'setValue' with an argument list of type '(value: WeakReference, forKey: String)'

Xcode version: Xcode 7.0 beta 1. Deployment targets tried: 10.9, 10.10 and 10.11.

EDIT: I have tried using NSValue, as per @rickster's suggestion, but the error remains:

layer.setValue(value: NSValue(nonretainedObject: self), forKey: "ActionViewItem")

ActionView.swift:72:19: Cannot invoke 'setValue' with an argument list of type '(value: NSValue, forKey: String)'

Answer 1

The setValue(_:forKey:) method requires an ObjC object for the value — you're passing an instance of a pure Swift class. If you make your WeakReference class either annotated with @objc or inherit from NSObject that call should succeed.

However, you don't need your own class for this purpose anyway... The NSValue method valueWithNonretainedObject does the same thing.

---

Oh, and on closer inspection: you're using an extra argument label in your call. It should be like setValue(myvalue, forKey: mykey).