Check modifierFlags of NSEvent if a certain modifier was pressed but no other - objective-c

Question

I just experimented with the addLocalMonitorForEventsMatchingMask:handler: method in NSEvent and came across the following question: How do I find out if only certain modifiers were pressed?
A short example to set this question into context: I wanted to listen for the shortcut "⌘+W". Therefore I wrote the following code:
[NSEvent addLocalMonitorForEventsMatchingMask:NSKeyDownMask handler:^(NSEvent *theEvent) {
if ([theEvent modifierFlags] & NSCommandKeyMask && [theEvent keyCode] == 13) {
[self.window performClose:self];
}
return theEvent;
}];
This works well, however the shortcut will be triggered, even if more modifier keys are pressed, e.g. "⌃+⌘+W" or "⇧+⌃+⌥+⌘+W". Is there a way to circumvent this?
A simple solution would be to check for all other modifier keys and ensure they are not pressed. This seems tedious and error prone - besides it's ugly enough as it is now with the unary "&". In addition you may get into trouble if (for some reason) another modifier key is added to keyboard layouts.
As always I'm thankful for any recommendations.

Answer 1

I think this'll do it:
// Mask out everything but the key flags
NSUInteger flags = [theEvent modifierFlags] & NSEventModifierFlagDeviceIndependentFlagsMask;
if( flags == NSCommandKeyMask ){
// Got it!
}
Hat tip to SpaceDog for pointing out the deprecation of the original mask name, NSDeviceIndependentModifierFlagsMask.

Answer 2

Swift 5 version
if event.modifierFlags.intersection(.deviceIndependentFlagsMask) == .command {
// Got it!
}

Answer 3

#JoshCaswell answer has been outdated thanks to Apple, because NSDeviceIndependentModifierFlagsMask has been deprecated since 10.12.
His answer updated to the new syntax is
// Mask out everything but the key flags
NSUInteger flags = [theEvent modifierFlags] & NSEventModifierFlagDeviceIndependentFlagsMask;
if( flags == NSCommandKeyMask ){
// Got it!
}
NSDeviceIndependentModifierFlagsMask has been replaced with NSEventModifierFlagDeviceIndependentFlagsMask because it makes a world of difference...

Answer 4

Maybe even better...
if event.modifierFlags.contains(.shift){
// do it
}