addGlobalMonitorForEventsMatchingMask not working

Question

I am having trouble with getting an assistive-enabled application (XCode in the development case) to capture global keyDown events. I've seen lots of code examples like the below, but this doesn't work for me on 10.9.4.

#import <AppKit/AppKit.h>
#import <Foundation/Foundation.h>

// 10.9+ only, see this url for compatibility:
// http://stackoverflow.com/questions/17693408/enable-access-for-assistive-devices-programmatically-on-10-9
BOOL checkAccessibility()
{
  NSDictionary* opts = @{(__bridge id)kAXTrustedCheckOptionPrompt: @YES};
  return AXIsProcessTrustedWithOptions((__bridge CFDictionaryRef)opts);
}

int main(int argc, const char * argv[])
{
  @autoreleasepool {
    if (checkAccessibility()) {
        NSLog(@"Accessibility Enabled");
    }
    else {
        NSLog(@"Accessibility Disabled");
    }

    NSLog(@"registering keydown mask");
    [NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask
                                           handler:^(NSEvent *event){
                                               NSLog(@"keydown: %@", event.characters);

                                           }];

      NSLog(@"entering run loop.");
      [[NSRunLoop currentRunLoop] run];
    }
    return 0;
}

The output received is:

2014-08-25 17:26:36.054 test[64725:303] Accessibility Enabled
2014-08-25 17:26:36.055 test[64725:303] registering keydown mask
2014-08-25 17:26:36.067 test[64725:303] entering run loop.

Once here, no other logging occurs, regardless of which keys I hit or what application has focus when I hit them.

FWIW, I'm trying to write an assistive application, not a key-logger or other evil thing. I've looked at the other instances of this question, but they seem to deal with either 1) the application not being assistive-enabled or 2) not receiving certain 'special' command keys that one would need CGEvents to receive. I am not seeing any keys, even simple ones (it's been running through my typing of this post and nothing was logged). TIA!

Answer 1

So, thanks to Ken Thomases' question above, I was able to work out how to do this. The key detail is that I am using a command line application template (I don't have any need for a UI, so I was trying to keep things minimal). News to me, but obvious in hindsight, just creating a run loop doesn't create an event loop. In order to replicate the creation of an event loop within a command line application, more of the guts of a typical cocoa application have to be brought into play. First, you have to have a class implementing the NSApplicationDelegate protocol, and that delegate will be where the application code lives, leaving the main method to simply do the following:

#import <Foundation/Foundation.h>
#include "AppDelegate.h"

int main(int argc, const char * argv[])
{
    @autoreleasepool {
        AppDelegate *delegate = [[AppDelegate alloc] init];

        NSApplication * application = [NSApplication sharedApplication];
        [application setDelegate:delegate];
        [NSApp run];
    }
}

This is a nib-less, menubar-less application, just like the usual command line application template, but it does have a true event loop, due to the [NSApp run] call. Then the application code that I used to have in my main method above moved into the app delegate:

#import "AppDelegate.h"

@implementation AppDelegate

// 10.9+ only, see this url for compatibility:
// http://stackoverflow.com/questions/17693408/enable-access-for-assistive-devices-programmatically-on-10-9
BOOL checkAccessibility()
{
    NSDictionary* opts = @{(__bridge id)kAXTrustedCheckOptionPrompt: @YES};
    return AXIsProcessTrustedWithOptions((__bridge CFDictionaryRef)opts);
}

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification
{
    if (checkAccessibility()) {
        NSLog(@"Accessibility Enabled");
    }
    else {
        NSLog(@"Accessibility Disabled");
    }

    NSLog(@"registering keydown mask");
    [NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask
                                           handler:^(NSEvent *event){
                                               NSLog(@"keydown: %@", event.characters);

                                           }];
}

@end

And just for completeness sake and future readers, the header file looks like this:

#import <AppKit/AppKit.h>
#import <Foundation/Foundation.h>

@interface AppDelegate : NSObject <NSApplicationDelegate>

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification;

@end