Question

I’m running into a thorny problem with posting an event from an event tap. I’m tapping for NSSystemDefined at kCGHIDEventTap, then replacing the event with a new one. The problem I’m running in to is that depending on how I post the event, it’s being seen only by some applications. My test applications are Opera, Firefox, Quicksilver, and Xcode. Here are the different techniques I’ve tried within my event tap callback, with results. I’m expecting an action (the “correct response”) from each app; “system beep” means the nothing-is-bound-to-that-key system sound.

1. Create a new event, and return it from the callback.
   Opera: no response/system beep, Firefox: no response/system beep, Quicksilver: correct response, Xcode: no response/system beep

2. Create a new event, post to kCGSessionEventTap with CGEventPost, return null.
   Opera: no response/system beep, Firefox: no response/system beep, Quicksilver: correct response, Xcode: no response/system beep

3. Create a new event, post to kCGAnnotatedSessionEventTap with CGEventPost, return null.
   Opera: correct response, Firefox: correct response, Quicksilver: no response/system beep, Xcode: no response/system beep

4. Create a new event, post with CGEventTapPostEvent, return null.
   Opera: no response/system beep, Firefox: no response/system beep, Quicksilver: correct response, Xcode: no response/system beep

5. Create a new event, post to kCGSessionEventTap with CGEventPost, and return new event.
   Opera: no response/system beep, Firefox: no response/system beep, Quicksilver: correct response, Xcode: no response/system beep

6. Create a new event, post to kCGAnnotatedSessionEventTap with CGEventPost, and return new event.
   Opera: correct response and system beep, Firefox: correct response and system beep, Quicksilver: correct response and system beep, Xcode: no response/double system beep

7. Create a new event, post with CGEventTapPostEvent, and return new event.
   Opera: no response/system beep, Firefox: no response/system beep, Quicksilver: correct response, Xcode: no response/system beep

(6) is the best, but users are complaining about the extra system beep on correct responses, which I’m guessing is coming from the double-posting of the event. I’m not sure of other combinations to try, or where else to look. Can anyone offer any guidance? Is there any way to get the results of both returning the event from my callback and posting to the annotated tap without doing both?

Sorry for the lengthy question; I’ve been doing a lot of experimenting.

Thanks in advance

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Update: this is the code I use to create the event tap:

CFMachPortRef eventTap;
eventTap = CGEventTapCreate(kCGHIDEventTap, kCGHeadInsertEventTap, 0,CGEventMaskBit(NX_SYSDEFINED) | (1 << kCGEventKeyDown) | (1 << kCGEventKeyUp), myCGEventCallback, (void *)hidEventQueue);

Answer 1

I think I fixed this. I had been using +[NSEvent keyEventWithType:location:modifierFlags:timestamp:windowNumber:context:characters:charactersIgnoringModifiers:isARepeat:keyCode:] to create an NSEvent, then returning that event’s -CGEvent. I switched to CGEventCreateKeyboardEvent, using the event source created from the original event with CGEventCreateSourceFromEvent, and returning the event from the callback. All my tests pass now.