How to receive a keyboard event (arrowkeys)

Question

Hi,
I'm a bit confused about how to setup event-handling for keyboard event. I have created a window with a File's Owner called "MyDocument". But if I implement the method
<pre>
-(void)sendEvent: (NSEvent *)theEvent {
printf("Called\n");
</pre>
it wont be called. Does anyone know what else I have to do in order to receive keyboard events when a user presses an arrowkey inside my application ?
Macbook Pro 15''   Mac OS X (10.4.8)   2GHz, 2GB

Answer 1

You most likely need to implement -(void)keyDown:(NSEvent *)event to catch keyboard events and then query event for the key pressed. This method is defined in NSResponder together with mouseDown:, mouseDragged, keyUp:, etc.
Here's a couple of examples from two sample apps:
'Dicey' (online sample code):
<pre>
-(void)keyDown:(NSEvent *)event {
// If the space bar was pressed, toggle hold on the first responder
if ([[event characters] isEqualToString:@" "]) {
[[dice objectAtIndex:firstResponderIndex] toggleHold];
[self setNeedsDisplay:YES];
} else {
// We do care about our superclass dealing with tab shift-tab for first responder changes
[super keyDown: event];
</pre>
'Worm' (From: /Developer/Examples/AppKit/Worm):
<pre>
- (void)keyDown:(NSEvent *)event {
NSString *keys = [event charactersIgnoringModifiers];
wormHeading = kGameHeadingStraight;
if (keys && [keys length] > 0) {
unichar c = [keys characterAtIndex:0];
if (c == NSLeftArrowFunctionKey) {
wormHeading = kGameHeadingLeft;
} else if (c == NSRightArrowFunctionKey) {
wormHeading = kGameHeadingRight;
</pre>
Note the use of NSLeftArrowFunctionKey for example in Worm. These and many other 'special' key constants are defined in NSEvent.