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invalid display identifier error while trying to make app full screen.

Forums > SwiftUI


Hello all,

I am working on a SwiftUI MacOS app that is simple note pad type app.

The app is a single window with a single TextEditor view, the unique feature of my app is that when my computer goes to sleep, the app window is made front and full screen so that when I return or wake my computer my notes are the first thing I see.

I am running into a couple bugs that I could use some guidance with.

  1. When I have an external monitor plugged into my laptop I get the following error and the app window will not go full screen or come to front: invalid display identifier 904CC364-346D-40EA-B050-8A3632616A77

  2. When I am running a browser (tested with Firefox and Safari) the app will also not go fullscreen but I get no errors.

Below is the relevant code from my App.swift file:

//  FullScreenApp.swift
//  FullScreen
//  Created by user on 6/18/23.
//import Foundation
import SwiftUI

struct FullScreenApp: App {

    var body: some Scene {
        Window("theWindow", id: "myWindow") {
               .onAppear {
                   DispatchQueue.main.asyncAfter(deadline: .now()) {
                       if let window = NSApplication.shared.windows.first {
                           window.backgroundColor = .white



        class AppDelegate: NSObject, NSApplicationDelegate, NSWindowDelegate {
                func applicationDidFinishLaunching(_ notification: Notification) {
                    let mainWindow = NSApp.windows[0]
                    mainWindow.delegate = self

                    mainWindow.standardWindowButton(.zoomButton)?.isHidden = true

                    //Lets add a listener thing here.

                    NSWorkspace.shared.notificationCenter.addObserver(self, selector: #selector(sleepListener(_:)), name: NSWorkspace.didWakeNotification, object: nil)

                func windowShouldClose(_ sender: NSWindow) -> Bool {
                    return false

            @objc private func sleepListener(_ aNotification: Notification) {
                    print("Listening for sleep")

                    if aNotification.name == NSWorkspace.didWakeNotification {
                        print("Did wake detected from App.swift file!")


                        if let wnd = NSApp.windows.first {

                            let isWindowFullscreen = wnd.styleMask.contains(.fullScreen)
                            print("is window full screen: \(isWindowFullscreen)")

                            //This brings the app to the most very front of everything.

                            print("Should be full screen")


                    } else if aNotification.name == NSWorkspace.didWakeNotification {
                        print("Woke up")
                    } else {
                        print("Some other event other than the first two")

        @NSApplicationDelegateAdaptor(AppDelegate.self) var appDelegate



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