Animate a custom property in a CALayer example.

MyLayer.m

//
//  MyLayer.m
//
//  Created by Chris Miles on 14/03/11.
//  Copyright 2011 Chris Miles.
//

/*

 Animate custom property example:
 
	double currentProgress = 1.0;
	CABasicAnimation *anim = [CABasicAnimation animationWithKeyPath:@"currentProgress"];
	anim.duration = 0.5;
	anim.fromValue = [NSNumber numberWithDouble:0.0];
	anim.toValue = [NSNumber numberWithDouble:currentProgress];
	anim.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];

	[myLayer addAnimation:anim forKey:@"animateProgress"];

	myLayer.currentProgress = currentProgress;
*/


#import <UIKit/UIKit.h>
#import <QuartzCore/QuartzCore.h>


@interface MyLayer : CALayer {
    double		currentProgress;
}

@property (nonatomic, assign)	double		currentProgress;

@end


@implementation MyLayer

@synthesize currentProgress;

+ (BOOL)needsDisplayForKey:(NSString *)key {
    // To force animation when our custom properties change
    BOOL result;
    if ([key isEqualToString:@"currentProgress"]) {
        result = YES;
    }
    else {
        result = [super needsDisplayForKey:key];
    }
    return result;
}

- (void)setCurrentProgress:(double)progress {
	// Force redraw outside of animations
	currentProgress = progress;
	[self setNeedsDisplay];
}

- (void)drawInContext:(CGContextRef)c {
	// Custom layer drawing
}

- (id)initWithLayer:(id)layer {
	if ((self = [super initWithLayer:layer])) {
		if ([layer isKindOfClass:[MyLayer class]]) {
			// Copy custom property values between layers
			MyLayer *other = (MyLayer *)layer;
			self.currentProgress = other.currentProgress;
		}
	}
	return self;
}

@end