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

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.

jscs · Accepted Answer · 2017-11-26T20:55:08.643

34

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.

edited Nov 26 '17 at 20:55

answered May 21 '11 at 20:44

jscs

63,694
13
151
195

5

Wow, that's neat! Now I have to use the unary "&" just once and finally understood what the `NSDeviceIndependentModifierFlagsMask` is for: The modifierFlags normally are set to 256 by default and other flags are added to it, this way I clean up so only the pressed keys are represented by the `modifierFlags` value. This way it's possible to write combinations of modifier keys like in Carbon, e.g. `flags == NSCommandKeyMask + NSControlKeyMas` if ⌘ **and** ⌃ should be pressed rather writing `flags & NSCommandKeyMask && flags & NSControlKeyMask`. Thanks a lot! – Florian Pilz May 22 '11 at 05:41
Pedantic mode dictates that masks should only be (bitwise) OR'd ('|'). Otherwise carry bits will come back to bite you. – geowar Feb 04 '16 at 16:50
`[theEvent modifierFlags] & (NSControlKeyMask|NSCommandKeyMask)` can be used for multiples – Yunus Nedim Mehel Jun 09 '16 at 13:28
1

unfortunately, thanks to Apple, NSDeviceIndependentModifierFlagsMask is deprecated. Back to the drawing board. – Duck Sep 29 '17 at 05:24

score 14 · Answer 2 · answered May 31 '19 at 06:30

14

Swift 5 version

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

answered May 31 '19 at 06:30

vicegax

4,709
28
37

score 6 · Answer 3 · answered Sep 29 '17 at 05:30

@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...

score 2 · Answer 4 · answered Apr 19 '21 at 17:26

2

Maybe even better...

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

answered Apr 19 '21 at 17:26

Marc T.

5,090
1
23
40

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

4 Answers4

Linked