Cocoa: Accepting and responding to keystrokes - cocoa

Question

Hey everyone, I'm a newbie and I have what I anticipate will be a pretty easy question to answer. In order to learn a bit about event handling and drawing, I'm attempting to write a program that draws a black rectangle that increases in length every time the user hits the 'c' key. So far it just draws a black rectangle on a blue background without responding to keystrokes. Here is what I have so far:
Input.h
#import <Cocoa/Cocoa.h>
#interface Input : NSView {
int length;
}
- (void)keyDown:(NSEvent *)theEvent;
#end
Input.m
#import "Input.h"
#implementation Input
- (id)initWithFrame:(NSRect)frame {
self = [super initWithFrame:frame];
length = 10;
if (self) {
// Initialization code here.
}
return self;
}
- (void)drawRect:(NSRect)dirtyRect {
//set variables
NSRect r1;
NSBezierPath *bp;
// set background color
[[NSColor blueColor] set];
NSRectFill(dirtyRect);
//set color to black & draw r1
[[NSColor blackColor] set];
r1 = NSMakeRect(1, 1, length, 10);
bp = [NSBezierPath bezierPathWithRect:r1];
[bp fill];
}
- (void)keyDown:(NSEvent *)theEvent
{
NSString *key = [theEvent characters];
if ( [key isEqualToString:#"c"] ) {
length += 10;
}
}
#end
I copied the keyDown method from Cocoa in a Nutshell, by the way. Needless to say, I don't really understand it. Do I have to make connections in IB in order to get the program to recognize keystrokes? Basically, I would love it if somebody could help me to get this program to work, because as of yet I have not gotten anything to respond to keystrokes.
And here's Cocoa in a Nutshell

Answer 1

IIRC, to receive keystrokes your view needs to become first responder. It should work if you add something like these methods:
- (BOOL) acceptsFirstResponder
{
return YES;
}
- (BOOL) resignFirstResponder
{
return YES;
}
- (BOOL) becomeFirstResponder
{
return YES;
}
(You can do other stuff in them too, of course, if appropriate.)
Update: You also need to mark your view as needing to be redrawn. Add:
[self setNeedsDisplay:YES];
To your event handler. And it's probably a good idea to add a log message at the beginning as well, so that you can see whether the method is getting called:
NSLog(#"keyDown [%#]", [theEvent characters]);