Keyboard event(CGEvent)'s flags is not correct

Question

I'm working on an app which encoding input characters into another language (Vietnamese) and I've facing with some issue of Apple documentation.

My code to listen for keyboard events is:

func cgEventCallback (
    proxy: CGEventTapProxy,
    type: CGEventType,
    event: CGEvent,
    refcon: UnsafeMutableRawPointer?
) -> Unmanaged<CGEvent>? {
    switch type {
    case .keyDown:
        print(event.flags, CGEventFlags.maskCommand)

        if (event.flags == CGEventFlags.maskCommand) {
            print("Flag is Command")
        } else {
            print("Flag is not Command")
        }

    default:
        break
    }

    return Unmanaged.passRetained(event)
}

As they said, CGEvent's flags returns the event flags of a Quartz event. So I expect that when I type in Command + C then it should print out:

CGEventFlags(rawValue: 1048576) CGEventFlags(rawValue: 1048576)
Flag is Command

But the issue is that the printed out text is not the same as expected:

CGEventFlags(rawValue: 1048840) CGEventFlags(rawValue: 1048576)
Flag is not Command

Am I misunderstanding about something or is there any way which could help me know what is the current flag of the event?

Martin R · Accepted Answer · 2021-01-24T13:10:12.930

1

event.flags is an OptionSet representing all flags for the current event. There can be more than one flag set, and that is what is happening in your case:

event.flags  = 1048840 (decimal) = 100108 (hex)
.maskCommand = 1048576 (decimal) = 100000 (hex)

So the correct test is

if event.flags.contains(.maskCommand) { ... }

instead of testing for equality.

edited Jan 24 '21 at 13:10

answered Jan 24 '21 at 13:04

Martin R

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Thanks for your answer @Martin R, I just have a small concern about this is that if I want to know the flags is currently in another OptionSet, e.g: [.maskCommand, .maskControl], to know that user is entering Control key or Command key? – Toan Quoc Ho Jan 24 '21 at 13:40
@ToanQuocHo: You can do `event.flags.isSuperset(of: [.maskCommand, .maskControl])` to test if the event flags contain any of the given flags. Is that what you are looking for? – Martin R Jan 24 '21 at 13:49
Yeah, I think something like that @Martin R, but something included inside flags which I don't know what it is. When I enter `Command` + `C` I hope that `event.flags.isSuperset(of: [.maskCommand, .maskControl])` to be true, but it's not. – Toan Quoc Ho Jan 24 '21 at 13:54
Flags = 256(not sure what it is, default maybe?) + 8(`C` character) + 1048576(.maskCommand) = 1048840. That's interesting, I thought that flags is simply just the .maskCommand but it combined all the characters already. – Toan Quoc Ho Jan 24 '21 at 14:24
Nevermind @MartinR, I've changed the approach to use Set of CGEventFlags and then use contains method to check it already. Thank you so much for your answer. – Toan Quoc Ho Jan 24 '21 at 14:45
@ToanQuocHo https://stackoverflow.com/a/41929189/2303865 and https://stackoverflow.com/a/32447474/2303865 – Leo Dabus Jan 24 '21 at 14:54
Thanks @LeoDabus, sadly that I'm using CGEvent and seems like it's a bit different than NSEvent. – Toan Quoc Ho Jan 24 '21 at 15:00
1

@ToanQuocHo I never said to use it as it is. Just a reference on how to switch an OptionSet. – Leo Dabus Jan 24 '21 at 15:06
1

Got that @LeoDabus, I've tried with isDisjoint and it works in my case. It was inspired by your comment though, thank you so much :D – Toan Quoc Ho Jan 24 '21 at 15:17

Keyboard event(CGEvent)'s flags is not correct

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