How does Apple update the Airport menu while it is open? (How to change NSMenu when it is already open)

Menu mouse tracking is done in a special run loop mode (NSEventTrackingRunLoopMode). In order to modify the menu, you need to dispatch a message so that it will be processed in the event tracking mode. The easiest way to do this is to use this method of NSRunLoop:

[[NSRunLoop currentRunLoop] performSelector:@selector(updateTheMenu:) target:self argument:yourMenu order:0 modes:[NSArray arrayWithObject:NSEventTrackingRunLoopMode]]

You can also specify the mode as NSRunLoopCommonModes and the message will be sent during any of the common run loop modes, including NSEventTrackingRunLoopMode.

Your update method would then do something like this:

- (void)updateTheMenu:(NSMenu*)menu
    [menu addItemWithTitle:@"Foobar" action:NULL keyEquivalent:@""];
    [menu update];

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