Make my Cocoa app respond to the keyboard play/pause key? - objective-c

Question

Is there a way to make my app respond to the play/pause button on Mac?
EDIT:
Using the suggested code,I get this console message:
Could not connect the action buttonPressed: to target of class NSApplication
Why would that be?

Answer 1

I accomplished this in my own application by subclassing NSApplication (and setting the app's principal class to this subclass). It catches seek and play/pause keys and translates them to specific actions in my app delegate.
Relevant lines:
#import <IOKit/hidsystem/ev_keymap.h>
- (void)sendEvent:(NSEvent *)event
{
// Catch media key events
if ([event type] == NSSystemDefined && [event subtype] == 8)
{
int keyCode = (([event data1] & 0xFFFF0000) >> 16);
int keyFlags = ([event data1] & 0x0000FFFF);
int keyState = (((keyFlags & 0xFF00) >> 8)) == 0xA;
// Process the media key event and return
[self mediaKeyEvent:keyCode state:keyState];
return;
}
// Continue on to super
[super sendEvent:event];
}
- (void)mediaKeyEvent:(int)key state:(BOOL)state
{
switch (key)
{
// Play pressed
case NX_KEYTYPE_PLAY:
if (state == NO)
[(TSAppController *)[self delegate] togglePlayPause:self];
break;
// Rewind
case NX_KEYTYPE_FAST:
if (state == YES)
[(TSAppController *)[self delegate] seekForward:self];
break;
// Previous
case NX_KEYTYPE_REWIND:
if (state == YES)
[(TSAppController *)[self delegate] seekBack:self];
break;
}
}
Edit:
Swift 4:
override func sendEvent(_ event: NSEvent)
{
if event.type == .systemDefined &&
event.subtype == .screenChanged
{
let keyCode : Int32 = (Int32((event.data1 & 0xFFFF0000) >> 16))
let keyFlags = (event.data1 & 0x0000FFFF)
let keyState = ((keyFlags & 0xFF00) >> 8) == 0xA
self.mediaKeyEvent(withKeyCode: keyCode, andState: keyState)
return
}
super.sendEvent(event)
}
private func mediaKeyEvent(withKeyCode keyCode : Int32, andState state : Bool)
{
guard let delegate = self.delegate as? AppDelegate else { return }
switch keyCode
{
// Play pressed
case NX_KEYTYPE_PLAY:
if state == false
{
delegate.musicPlayerWC.handleUserPressedPlayButton()
}
break
// Rewind
case NX_KEYTYPE_FAST:
if state == true
{
delegate.musicPlayerWC.handleUserPressedNextSongButton()
}
break
// Previous
case NX_KEYTYPE_REWIND:
if state == true
{
delegate.musicPlayerWC.handleUserPressedPreviousSongButton()
}
break
default:
break
}
}

Answer 2

Here's a great article on the subject: http://www.rogueamoeba.com/utm/2007/09/29/

Answer 3

Check this: https://gist.github.com/gauravk92/546311
Works perfectly.
As example, this repo uses it: https://github.com/onepill/PauseIt

Answer 4

In case anyone comes looking, there is sample code to do this here. This approach does allow you to "eat" the events they do not reach iTunes or other media-key-aware apps.
But be warned that event taps are not allowed by the sandbox, so this won't work in the App Store. If anyone has a workaround for that I'd love to hear it.