gistfile1.txt

import Cocoa

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
    @IBOutlet weak var window: NSWindow!
    @IBOutlet var objectController: NSObjectController!

    dynamic var foo: String = "" {
        didSet { print("did set foo to \(self.foo)") }
    }
    
    @IBAction func saveOrSomething(_ sender: Any) {
        self.objectController.commitEditing()
        
        print("as this is clicked, foo is '\(self.foo)'")
        
        // presumably, do something to save the data
    }
}