UI Save/Restoration mechanism in Cocoa via Swift

Question

I'd like to save the state of Check Box, quit application, then launch macOS app again to see restored state of my Check Box. But there's no restored state in UI of my app.

What am I doing wrong?

import Cocoa

class ViewController: NSViewController {

    @IBOutlet weak var tick: NSButton!

    override func viewDidLoad() {
        super.viewDidLoad()
    }

    override func encodeRestorableState(with coder: NSCoder) {
        super.encodeRestorableState(with: coder)
        coder.encode(tick.state, forKey: "")
    }

    override func restoreState(with coder: NSCoder) {
        super.restoreState(with: coder)       
        if let state = coder.decodeObject(forKey: "") as? NSControl.StateValue {
            tick.state = state
        }
    }
}

Answer 1

To the best of my knowledge, this is the absolute minimum you need to implement custom UI state restoration of a window and/or its contents.

In this example, I have a window with a checkbox and that checkbox's state represents some custom view state that I want to restore when the app is relaunched.

The project contains a single window with a single checkbox button. The button's value is bound to the myState property of the window's content view controller. So, technically, the fact that this is a checkbox control is irrelevant; we're actually going to preserve and restore the myState property (the UI takes care of itself).

To make this work, the window's restorable property is set to true (in the window object inspector) and the window is assigned an identifier ("PersistentWindow"). NSWindow is subclassed (PersistentWindow) and the subclass implements the restorableStateKeyPaths property. This property lists the custom properties to be preserved/restored.

Note: if you can define your UI state restoration in terms of a list of key-value compliant property paths, that is (by far) the simplest solution. If not, you must implement encodeRestorableState / restoreState and are responsible for calling invalidateRestorableState.

Here's the custom window class:

class PersistentWindow: NSWindow {

    // Custom subclass of window the perserves/restores UI state

    // The simple way to preserve and restore state information is to just declare the key-value paths
    //  of the properties you want preserved/restored; Cocoa does the rest
    override class var restorableStateKeyPaths: [String] {
       return [ "self.contentViewController.myState" ]
       }

    // Alternatively, if you have complex UI state, you can implement these methods
//  override func encodeRestorableState(with coder: NSCoder) {
//      // optional method to encode special/complex view state here
//  }
//  
//  override func restoreState(with coder: NSCoder) {
//      // companion method to decode special/complex view state
//  }

}

And here's the (relevant portion) of the content view controller

class ViewController: NSViewController {

    @objc var myState : Bool = false

    blah, blah, blah
}

(I built this as a Cocoa app project, which I could upload if someone tells me where I could upload it to.)