Animating CAShapeLayer's strokeColor with CABasicAnimation

Question

I've been unsuccessful at animating a flashing stroke on a CAShapeLayer using the answer from this previous thread, and after many searches I can find no other examples of animating the stroke using CABasicAnimation.

What I want to do is have the stroke of my CAShapeLayer pulse between two colors. Using CABasicAnimation for opacity works fine, but the [CABasicAnimation animationWithKeyPath:@"strokeColor"] eludes me, and I'd appreciate any advice on how to successfully implement.

    CABasicAnimation *strokeAnim = [CABasicAnimation animationWithKeyPath:@"strokeColor"];
    strokeAnim.fromValue         = (id) [UIColor blackColor].CGColor;
    strokeAnim.toValue           = (id) [UIColor purpleColor].CGColor;
    strokeAnim.duration          = 1.0;
    strokeAnim.repeatCount       = 0.0;
    strokeAnim.autoreverses      = NO;
    [shapeLayer addAnimation:strokeAnim forKey:@"animateStrokeColor"];

//    CABasicAnimation *opacityAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
//    opacityAnimation.fromValue         = [NSNumber numberWithFloat:0.0];
//    opacityAnimation.toValue           = [NSNumber numberWithFloat:1.0];
//    opacityAnimation.duration          = 1.0;
//    opacityAnimation.repeatCount       = 0.0;
//    opacityAnimation.autoreverses      = NO;
//    [shapeLayer addAnimation:opacityAnimation forKey:@"animateOpacity"];

Uncommenting the opacity animation results in an expected opacity fade. The stroke animation produces no effect. An implicit strokeColor change animates as expected, but I would like documented confirmation that strokeColor can be explicitly animated using CABasicAnimation.

Update: The specific problem was that shapeLayer.path was NULL. Correcting that fixed the problem.

Answer 1

The code below works great for me. What is the lineWidth of your shapeLayer stroke path? Could that be the issue?

- (void)viewDidLoad
{
    [super viewDidLoad];

    UIBezierPath * circle = [UIBezierPath bezierPathWithOvalInRect:self.view.bounds];

    CAShapeLayer * shapeLayer = [CAShapeLayer layer];
    shapeLayer.path = circle.CGPath;
    shapeLayer.strokeColor =[UIColor blueColor].CGColor;
    [shapeLayer setLineWidth:15.0];

    [self.view.layer addSublayer:shapeLayer];

    CABasicAnimation *strokeAnim = [CABasicAnimation animationWithKeyPath:@"strokeColor"];
    strokeAnim.fromValue         = (id) [UIColor redColor].CGColor;
    strokeAnim.toValue           = (id) [UIColor greenColor].CGColor;
    strokeAnim.duration          = 3.0;
    strokeAnim.repeatCount       = 0;
    strokeAnim.autoreverses      = YES;
    [shapeLayer addAnimation:strokeAnim forKey:@"animateStrokeColor"];

}

Let me know if it works for you...