在 OS X 中监听键盘按下

#import <Foundation/Foundation.h>

@interface KeyboardObserver : NSObject

@property (nonatomic) CFMachPortRef port;

- (void)start;

@end

@implementation KeyboardObserver

- (instancetype)init {
    self = [super init];
    if (self) {
        CFRunLoopSourceRef source = CGEventTapCreate(
            NULL,                                       // 管道
            kCGEventTapOptionDefault,                  // 捕获模式
            CGEventTypeKeyboardKeyDown,              // 事件类型
            self,                                        // 目标对象
            (CFStringRef)@"keyboard_event"          // 事件名称
        );
        if (!source) {
            NSLog(@"Failed to create event tap!");
            return self;
        }
        self->port = CFMachPortCreate(NULL, source, NULL);
        CFRunLoopAddSource(CFRunLoopGetCurrent(), source, kCFRunLoopCommonModes);
        CGEventTapEnable(self->port, true);
    }
    return self;
}

- (void)dealloc {
    if (self->port) {
        CGEventTapEnable(self->port, false);
        CFRunLoopRemoveSource(CFRunLoopGetCurrent(), self->port, kCFRunLoopCommonModes);
        CFRelease(self->port);
    }
    [super dealloc];
}

- (void)start {
    dispatch_async(dispatch_get_main_queue(), ^{
        [[NSRunLoop currentRunLoop] run];
    });
}

@end

int main(int argc, const char *argv[]) {
    @autoreleasepool {
        KeyboardObserver observer = [[KeyboardObserver alloc] init];
        [observer start];
        [[NSRunLoop currentRunLoop] run];
    }
    return 0;
}