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Abstract

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To be sent keyboard events destined for other applications, you can use a Carbon event handler targeting the “event monitor” target. There a few ‘gotchas’ which make this unique in Cocoa.

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Requirements

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The only requirement for this to work is that “Enable access for assistive devices” is turned on in “Universal Access” when monitoring keyboard events in other apps.

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Carbon Code

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Simple Carbon code for this can be found in Apple’s EventMonitorTest sample code project.

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Cocoa Code

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Mac OS X 10.4 does some trickery behind the scenes to make the key down and key up events get sent to NSApplication -sendEvent: rather than the event handler. So in this case, you’ll need a subclass of NSApplication to handle that. In Mac OS X 10.5, this no longer happens. Instead, you’ll receive all events through the event handler as you would in a Carbon application.

For 10.4, the following code applies:

// // MyApplication.h //

#import <Cocoa/Cocoa.h> #import <Carbon/Carbon.h>

@interface MyApplication : NSApplication { EventHandlerRef mMonitorHandlerRef; }

• (void)installMonitorHandler;
• (void)uninstallMonitorHandler;

@end

// // MyApplication.h //

#import “MyApplication.h”

@implementation MyApplication

• (void)installMonitorHandler; { OSStatus error = noErr; EventTypeSpec kEvents[] = { { kEventClassKeyboard, kEventRawKeyDown }, { kEventClassKeyboard, kEventRawKeyUp } };

  // the magic happens here with the call to GetEventMonitorTarget as described in CarbonEvents.h // The event monitor target is a special event target used to monitor user input events across all processes. // When the monitor target detects a matching event, then MonitorHandler is called. error = InstallEventHandler( GetEventMonitorTarget(), MonitorHandler, GetEventTypeCount( kEvents ), kEvents, NULL, &mMonitorHandlerRef ); if (error != noErr) { NSBeep(); NSLog(@”InstallEventHandler error %d”, error); } }

• (void)uninstallMonitorHandler; { if (mMonitorHandlerRef) { RemoveEventHandler(mMonitorHandlerRef); mMonitorHandlerRef = NULL; } }

• (void)sendEvent:(NSEvent *)event; { NSEventType eventType = [event type];

  // Catch keyboard events destined for other apps when recording if (![self isActive] && (eventType == NSKeyDown || eventType == NSKeyUp || eventType == NSFlagsChanged)) { NSLog(@”sendEvent: interior”); return; }

  [super sendEvent:event]; }

static OSStatus MonitorHandler(EventHandlerCallRef nextHandler, EventRef theEvent, void * inRefcon) { // Useless on 10.4 for keyboard events. If you requested to watch other events // (mouse or tablet events for example) they would into funnel to here. return CallNextEventHandler(nextHandler, theEvent); }

@end

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Related Topics

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[Topic]