How to handle arrow key event in Cocoa app?

问题

回答1:

But, but, but...I don't wanna be an NSResponder subclass.

@interface AMonitorNotAResponder : NSObject 
@end

@implementation AMonitorNotAResponder
{
    id eventMonitor;   // An event monitor object; instance of
                       // private class _NSLocalEventObserver
}

- (id)init 
{
    self = [super init];
    if( !self ) return nil;

    NSEvent * (^monitorHandler)(NSEvent *);
    monitorHandler = ^NSEvent * (NSEvent * theEvent){

        switch ([theEvent keyCode]) {
            case 123:    // Left arrow
                NSLog(@"Left behind.");
                break;
            case 124:    // Right arrow
                NSLog(@"Right as always!");
                break;
            case 125:    // Down arrow
                NSLog(@"Downward is Heavenward");
                break;
            case 126:    // Up arrow
                NSLog(@"Up, up, and away!");
                break;
            default:
                break;
        }
        // Return the event, a new event, or, to stop 
        // the event from being dispatched, nil
        return theEvent;
    };

    // Creates an object we do not own, but must keep track
    // of so that it can be "removed" when we're done
    eventMonitor = [NSEvent addLocalMonitorForEventsMatchingMask:NSKeyDownMask 
                                                         handler:monitorHandler];

    return self;
}

- (void)dealloc 
{
    [NSEvent removeMonitor:eventMon];
}

@end

The Event Handling Guide gives some possible uses. Seems to be a friendly Cocoa version of the CGEventTap, or a way to bypass the responder chain for some specific purpose. There's a limited selection of event types that can be monitored, e.g, only key down, not up. The docs have the list.

Also available: inspect events going to any other application (without being able to modify them) using addGlobalMonitorForEventsMatchingMask:handler:. Like event taps, this method requires Accessibility to be turned on.

回答2:

See this code. I assumed the class is subclass of NSView.

#pragma mark    -   NSResponder

- (void)keyDown:(NSEvent *)theEvent
{
    NSString*   const   character   =   [theEvent charactersIgnoringModifiers];
    unichar     const   code        =   [character characterAtIndex:0];

    switch (code) 
    {
        case NSUpArrowFunctionKey:
        {
            break;
        }
        case NSDownArrowFunctionKey:
        {
            break;
        }
        case NSLeftArrowFunctionKey:
        {
            [self navigateToPreviousImage];
            break;
        }
        case NSRightArrowFunctionKey:
        {
            [self navigateToNextImage];
            break;
        }
    }
}

A view should be first responder to receive events. Maybe this code will be required to support that.

#pragma mark    -   NSResponder
- (BOOL)canBecomeKeyView
{
    return  YES;
}
- (BOOL)acceptsFirstResponder
{
    return  YES;
}

To use this method, the class should be subclass of NSResponder. See the other answer handling without subclassing NSResponder.

回答3:

In my case I wanted a presented NSViewController subclass to be able to listen to arrow key events for navigation with minimal effort. Here's the best solution I've found, a slight variation of Josh Caswell's answer.

Define an event monitor (optional), can be locally in your NSViewController subclass .m

id keyMonitor;

Then start monitoring events, for example in viewDidLoad.

keyMonitor = [NSEvent addLocalMonitorForEventsMatchingMask:NSKeyDownMask handler:^(NSEvent *event) {

    unichar character = [[event characters] characterAtIndex:0];
    switch (character) {
        case NSUpArrowFunctionKey:
            NSLog(@"Up");
            break;
        case NSDownArrowFunctionKey:
            NSLog(@"Down");
            break;
        case NSLeftArrowFunctionKey:
            NSLog(@"Left");
            break;
        case NSRightArrowFunctionKey:
            NSLog(@"Right");
            break;
        default:
            break;
    }
    return event;
}];

To remove the monitor when not required (assuming you defined it)

[NSEvent removeMonitor:keyMonitor];

来源：https://stackoverflow.com/questions/6000133/how-to-handle-arrow-key-event-in-cocoa-app

标签

cocoa

keyboard-events