applicationWillTerminate does not get invoked

I want to save my data before terminating, so my AppControll class conforms the NSApplicationDelegate pro开发者_C百科tocol, and declared the method; and in the interface builder I bound the window's delegate outlet to AppController, but I cannot get the method invoked.

Where I am wrong, what should I do?

Are you terminating the app from Xcode? Alternatively, is sudden termination enabled in your Info.plist?

Either of these will cause a SIGTERM signal to be sent to the application, terminating it immediately, with no chance for the NSApplication instance to send its delegate an applicationWillTerminate: message. (This is the point of sudden termination: Your app dies instantly. You can turn it off and on programmatically for times when this would be bad.)

Try quitting your application within itself (the Quit menu item in your Application menu), or using the Dock to quit it (right-click on your application's tile and choose “Quit”). As long as sudden termination is disabled (or never was enabled), either of these will cause your application object to send the applicationWillTerminate: message.

Also check that your delegate is getting sent other application-delegate messages, such as applicationWillFinishLaunching:, and make sure you hooked up the outlet in the correct nib (your MainMenu nib).

Did you remember to add the handler to the application?

UIApplication *app = [UIApplication sharedApplication];
[[NSNotificationCenter defaultCenter] 
   addObserver:self
   selector:@selector(applicationWillTerminate:)
   name:UIApplicationWillTerminateNotification object:app];

Is multitasking still enabled? That could be the problem - tapping the home button doesn't cause applicationWillTerminate: to be called if the app goes into the background.

I'm assuming this question applies to macOS apps (as it mentions NSApplicationDelegate).

By default, Xcode 11 (and maybe earlier versions?) includes the NSSupportsSuddenTermination property in new applications' Info.plist file:

  ...
  <key>NSSupportsSuddenTermination</key>
  <true/>
  ...

This property is associated with the enableSuddenTermination and disableSuddenTermination pair of methods in the ProcessInfo (NSProcessInfo) class.

The relevant part of ProcessInfo documentation states:

Sudden Termination

macOS 10.6 and later includes a mechanism that allows the system to log out or shut down more quickly by, whenever possible, killing applications instead of requesting that they quit themselves.

Your application can enable this capability on a global basis and then manually override its availability during actions that could cause data corruption or a poor user experience by allowing sudden termination. Alternately, your application can just manually enable and disable this functionality.

In other words, when NSSupportsSuddenTermination is true, when the user tries to quit the application (directly or indirectly), macOS terminates it, instead of requesting it to quit. This bypasses any events that would otherwise be triggered during a regular quit request.

The good new is that you can either disable that in the Info.plist file, or manually override it, according to your application's needs, by calling ProcessInfo.processInfo.disableSuddenTermination().

In applicationWillFinishLaunching: add:

[[NSNotificationCenter defaultCenter]
    addObserver:self
    selector:@selector(applicationWillTerminate:)
    name:UIApplicationWillTerminateNotification object:nil];