Subclassed NSView to notify ViewController of action

Question

I have subclassed NSView to receive a dropped folder in order to get its URL. I've been getting the URL to my ViewController class by accessing a property set in my custom NSView class.

import Cocoa

class DropView: NSView {
    var droppedURL : URL!

    override func draw(_ dirtyRect: NSRect) {
        super.draw(dirtyRect)

        // Drawing code here.
    }
    public required init?(coder: NSCoder) {
        super .init(coder: coder)
        registerForDraggedTypes([NSPasteboard.PasteboardType.fileURL])
    }
    
    public override func draggingEntered(_ sender: NSDraggingInfo) -> NSDragOperation {
        return NSDragOperation.copy
    }
    public override func draggingUpdated(_ sender: NSDraggingInfo) -> NSDragOperation {
        NSDragOperation.copy
    }
    public override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
        let pboard = sender.draggingPasteboard
        let urlString = pboard.string(forType: NSPasteboard.PasteboardType.fileURL)
        let folderURL = URL(string: urlString!)
        print(folderURL)
        droppedURL = folderURL
        return true
    }
    
}

How can I let my ViewController know when a folder has been dropped onto my NSView and that a URL has been successfully captured? Is there a way other than posting a notification?

Answer 1

Usually you'd use delegates or closures for this. I prefer closures because they're so clean, but it's up to you.

First, define your closure in DropView:

class DropView: NSView {
    var droppedURL : URL!
    var droppedSuccessfully: ((URL) -> Void)? /// here!

Then, call it just like how you'd call a function. Make sure to pass in your folderURL too.

public override func performDragOperation(_ sender: NSDraggingInfo) -> Bool {
    let pboard = sender.draggingPasteboard
    let urlString = pboard.string(forType: NSPasteboard.PasteboardType.fileURL)
    let folderURL = URL(string: urlString!)
    print(folderURL)
    droppedURL = folderURL
    droppedSuccessfully?(folderURL) /// here!
    return true
}

Finally, assign the closure back in your ViewController.

override func viewDidLoad() {
    super.viewDidLoad()

    ...
                                         /// prevent retain cycle
    yourDropView.droppedSuccessfully = { [weak self] url in
        print("URL received: \(url)")
    }
}