macos-fullscreenmode-test

Goal

To be able to react when a screen has been disconnected while an application's view is in full screen mode using NSView enterFullScreenMode.

UPDATES

2020-06-26: I have opened a case with Apple Developer Support and am working through this issue with engineers there but there is no resolution yet.

2020-11-20: This application does get the desired notifications via all three below notification methods on a 2020 M1 Mac Mini running macOS Big Sur 11.0.1 when the display is captured. Testing on a 2018 Mac Mini running 11.0.1 still does not receive the notifications. I've updated Apple dev support with this information.

Problem

It appears that when a view is in full screen mode, there's no way to get a notification from macOS.

I've tried all three methods I know of:

• [NSApplicationDelegate's applicationDidChangeScreenParameters] (https://developer.apple.com/reference/appkit/nsapplicationdelegate/1428424-applicationdidchangescreenparame)
• Registering with NotificationCenter for [NSApplicationDidChangeScreenParameters] (https://developer.apple.com/reference/foundation/nsnotification.name/1428749-nsapplicationdidchangescreenpara)
• Core Graphics [CGDisplayRegisterReconfigurationCallback] (https://developer.apple.com/reference/coregraphics/1455336-cgdisplayregisterreconfiguration?language=objc)

And none of them seem to get notifications when a screen disconnects when in full screen mode.

This is probably related to the fact that macOS's System Preferences > Displays cannot change the resolution of any display while a view is in full screen mode.

Cause

As kinda documented in CGDisplayCapture, if a display is captured by Core Graphics, displays cannot have their configurations changed.

Testing

Run the included application with at least one external screen.

Click the "Enter" button to start full screen mode.

Disconnect a display. Note: If you get a black screen, just hit command-Q to quit the application.

Mitigating

1. Perhaps periodically release the display to allow notifications to present and then recapture?
2. Do views get notifications of parameters changing when in full screen mode?