NSWindowDelegate not getting resize notifications

Question

In a macOS Cocoa app, I am trying to get notifications when my window is "corner dragged" to a new size by setting an NSWindow delegate. I am successfully getting notified of resize events when the window is initially created, but not when the window is later dragged to a new size. I can't figure out why not.

Here is my code:

class MyWindowController: NSWindowController {
    override func windowDidLoad() {
        super.windowDidLoad()
        window?.delegate = self
    }
}

extension MyWindowController: NSWindowDelegate {
    func windowDidResize(_ notification: Notification) {
        print("windowDidResize")
    }
    
    func windowWillResize(_ sender: NSWindow, to frameSize: NSSize) -> NSSize {
        print("windowWillResize")
        return frameSize
    }
}

When the window is first created, I see this output:

windowWillResize
windowDidResize

which proves the delegate methods are working. However, when I then grab a corner of the window and resize it, I do not see any additional print output.

I have reviewed a number of similar questions on SO about getting these notifications (like this and this), and it seems like I am doing everything right. And yet I don't get the notifications on window corner drag resize. Does anyone know why?

Answer 1

Based on the comment from Willeke, I created a strong reference to the NSWindowController subclass in my AppDelegate (where the window is created) and it fixed the problem.

For people finding this in the future, this is how I created in the strong reference (in AppDelegate):

// Need to maintain a strong reference while window is open
var myWindowController : MyWindowController?

[...]

func funcThatCreatesWindow() {
  [...]
  self.myWindowController = storyboard.instantiateController(withIdentifier: storyboardID) as? MyWindowController
  if self.myWindowController != nil {
    myWindowController!.showWindow(nil)
  }
}