在Cocoa状态栏应用程序中接收按键和按键事件

如果没有窗口,您希望接收什么类型的关键事件?

如果您需要在全球范围内拦截关键事件,那么您将需要使用Quartz事件tap。您必须非常小心,因为在事件中引发异常tap处理程序可能会冻结窗口服务器,因此您应该有适当的异常处理。

#import <ApplicationServices/ApplicationServices.h>

//assume CGEventTap eventTap is an ivar or other global

void createEventTap(void)
{
 CFRunLoopSourceRef runLoopSource;

 ///we only want keydown events
 CGEventMask eventMask = (1 << kCGEventKeyDown);

 // Keyboard event taps need Universal Access enabled, 
 // check whether we're allowed to attach an event tap
 if (!AXAPIEnabled()&&!AXIsProcessTrusted()) { 
  // error dialog here 
  NSAlert *alert = [[[NSAlert alloc] init] autorelease];
  [alert addButtonWithTitle:@"OK"];
  [alert setMessageText:@"Could not start event monitoring."];
  [alert setInformativeText:@"Please enable \"access for assistive devices\" in the Universal Access pane of System Preferences."];
  [alert runModal];
  return;
 } 


 //create the event tap
 eventTap = CGEventTapCreate(kCGHIDEventTap, //this intercepts events at the lowest level, where they enter the window server
        kCGHeadInsertEventTap, 
        kCGEventTapOptionDefault, 
        eventMask,
        myCGEventCallback, //this is the callback that we receive when the event fires
        nil); 

 // Create a run loop source.
 runLoopSource = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, eventTap, 0);

 // Add to the current run loop.
 CFRunLoopAddSource(CFRunLoopGetCurrent(), runLoopSource, kCFRunLoopCommonModes);

 // Enable the event tap.
 CGEventTapEnable(eventTap, true);
}


//the CGEvent callback that does the heavy lifting
CGEventRef myCGEventCallback(CGEventTapProxy proxy, CGEventType type, CGEventRef theEvent, void *refcon)
{
 //handle the event here
 //if you want to capture the event and prevent it propagating as normal, return NULL.

 //if you want to let the event process as normal, return theEvent.
 return theEvent;
}

当然,答案很简单:

[NSApp currentEvent]; 

返回任何Cocoa应用程序中的当前事件。