swift property observer on reference property - swift

Question

How do you get a reference property to trigger a property observer?
In order to demonstrate my problem I wrote a simple MVC program with one button and one label. The button increments a counter in the model and displays the value of the counter in the label in the view controller.
The problem is that the counter increment (in the model) does not trigger the didSet observer ( in the view controller)
Here is the model file:
import Foundation
class MvcModel {
var counter: Int
var message: String
init(counter: Int, message: String) {
self.counter = counter
self.message = message
}
}
// create instance
var model = MvcModel(counter: 0, message: "" )
// counting
func incrementCounter() {
model.counter += 1
model.message = "Counter Value: \(model.counter)"
//print(model.message)
}
Here is the view controller file:
import Cocoa
class ViewController: NSViewController {
let model1 = model
var messageFromModel = model.message {
didSet {
updateDisplayCounterLabel()
}
}
// update Label
func updateDisplayCounterLabel() {
DisplayCounterLabel.stringValue = model1.message
}
// Label
#IBOutlet weak var DisplayCounterLabel: NSTextField! {
didSet {
DisplayCounterLabel.stringValue = "counter not started"
}
}
// Button
#IBAction func IncrementButton(_ sender: NSButton) {
incrementCounter()
print("IBAction: \(model1.message)")
}
}
I guess the problem is linked to reference property (as I have been able to make this program work with a model based on a struct).
I would appreciate if someone could tell me how to deal with property observers and reference property and make this kind of MVC work as I plan to use it in real programs.

Answer 1

You could create a delegate for MvcModel
protocol MvcModelDelegate {
func didUpdateModel(counter:Int)
}
next you add a delegate property to MvcModel
class MvcModel {
var counter: Int {
didSet {
delegate?.didUpdateModel(counter: counter)
}
}
var message: String
var delegate: MvcModelDelegate?
init(counter: Int, message: String) {
self.counter = counter
self.message = message
}
}
then you make the ViewController class conform to MvcModelDelegate and finally you set model.delegate = self into the viewDidLoad
class Controller: UIViewController, MvcModelDelegate {
let model = MvcModel(counter: 0, message: "hello")
override func viewDidLoad() {
super.viewDidLoad()
self.model.delegate = self
}
func didUpdateModel(counter: Int) {
print("new value for counter \(counter)")
}
}

Answer 2

In case someone is interested here is the code as suggested by Noam.
Model File:
import Foundation
protocol MvcModelDelegate {
func didUpDateModel(message: String)
}
class MvcModel {
var counter: Int
var message: String {
didSet {
delegate?.didUpDateModel(message: message)
}
}
var delegate: MvcModelDelegate?
init(counter: Int, message: String) {
self.counter = counter
self.message = message
}
}
// create instance
var model = MvcModel(counter: 0, message: "" )
// counting
func incrementCounter() {
model.counter += 1
model.message = "Counter Value: \(model.counter)"
}
}
View Controller File
import Cocoa
class ViewController: NSViewController, ModelDelegate {
// communication link to the model
var model1 = model
var messageFromModel = messageToLabel
override func viewDidLoad() {
super.viewDidLoad()
self.model1.delegate = self
}
// update display
func didUpdateModel(message: String) {
//self.Label1.stringValue = model1.message
self.Label1.stringValue = messageFromModel
}
// Label
#IBOutlet weak var Label1: NSTextField! {
didSet {
Label1.stringValue = " counter not started"
}
}
// Button
#IBAction func testButton(_ sender: NSButton) {
incrementCounter()
}
}