gistfile1.txt

@implementation MHButton
{
	BOOL observing;           // whether we're listening to changes in state
	BOOL didDrawHighlighted;  // used to optimize drawing
	BOOL didDrawEnabled;      // used to optimize drawing
}

@synthesize appearance;

- (void)setAppearance:(id <MHButtonAppearance>)newAppearance
{
	if (appearance != newAppearance)
	{
		appearance = newAppearance;

		if (!observing)
		{
			[self addObserver:self forKeyPath:@"highlighted" options:NSKeyValueObservingOptionNew context:NULL];
			[self addObserver:self forKeyPath:@"enabled" options:NSKeyValueObservingOptionNew context:NULL];
			observing = YES;
		}
	}
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
	BOOL changed = NO;
	BOOL newState = [[change objectForKey:NSKeyValueChangeNewKey] intValue];

	// We'll receive a lot of notifications but we only want to redraw when the
	// state actually did change. (Observing these properties works better than
	// overriding touches on the button.)
	if ([keyPath isEqualToString:@"highlighted"])
		changed = (newState != didDrawHighlighted);
	else if ([keyPath isEqualToString:@"enabled"])
		changed = (newState != didDrawEnabled);

	if (changed)
		[self setNeedsDisplay];
}

- (void)dealloc
{
	if (observing)
	{
		[self removeObserver:self forKeyPath:@"highlighted"];
		[self removeObserver:self forKeyPath:@"enabled"];
	}
}

- (void)drawRect:(CGRect)rect
{
	if (self.appearance != nil)
	{
		CGContextRef context = UIGraphicsGetCurrentContext();
		[self.appearance button:self drawRect:rect inContext:context];
	}

	didDrawHighlighted = self.highlighted;
	didDrawEnabled = self.enabled;
}

@end