Flickering in simple animation chain - ios

Question

I'm trying to animate a pulsting circle. But after the downward scale, there's something of a flickering effect. Any ideas to why that is? Here's my code so far:
- (instancetype)init
{
self = [super init];
if (self) {
if (!self.path) {
self.path = [UIBezierPath bezierPathWithArcCenter:CGPointMake(0, 0) radius:7 startAngle:0.0*(M_PI/180.0) endAngle:360.0*(M_PI/180.0) clockwise:YES].CGPath;
}
[self animateCircleUpward];
}
return self;
}
-(void)animateCircleUpward {
[CATransaction begin];
[CATransaction setCompletionBlock:^{[self animateCircleDownward];}];
CABasicAnimation * scaleUpwardAnimation = [CABasicAnimation animationWithKeyPath:#"transform.scale.xy"];
scaleUpwardAnimation.fromValue = #(0.7);
scaleUpwardAnimation.toValue = #(1.0);
CABasicAnimation *opacityAnimation = [CABasicAnimation animationWithKeyPath:#"opacity"];
opacityAnimation.fromValue = #(1.0);
opacityAnimation.toValue = #(0.6);
self.fillColor = [UIColor greenColor].CGColor;
CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
NSArray *animations = #[scaleUpwardAnimation, opacityAnimation];
animationGroup.duration = 0.4;
animationGroup.animations = animations;
[self addAnimation:animationGroup forKey:#"pulse"];
[CATransaction commit];
}
-(void)animateCircleDownward {
[CATransaction begin];
[CATransaction setCompletionBlock:^{[self animateCircleUpward];}];
CABasicAnimation * scaleDownwardAnimation = [CABasicAnimation animationWithKeyPath:#"transform.scale.xy"];
scaleDownwardAnimation.fromValue = #(1.0);
scaleDownwardAnimation.toValue = #(0.7);
CABasicAnimation *opacityAnimation = [CABasicAnimation animationWithKeyPath:#"opacity"];
opacityAnimation.fromValue = #(0.6);
opacityAnimation.toValue = #(1.0);
self.fillColor = [UIColor greenColor].CGColor;
CAAnimationGroup *animationGroup = [CAAnimationGroup animation];
NSArray *animations = #[scaleDownwardAnimation, opacityAnimation];
animationGroup.duration = 0.4;
animationGroup.animations = animations;
[self addAnimation:animationGroup forKey:#"pulse"];
[CATransaction commit];
}
#end
Thanx in advance!

Answer 1

In regards to your actual question you likely need to set your CAAnimationGroup's fillMode property to kCAFillModeForward. The default value is kCAFillModeRemoved, so you are likely glimpsing the non-presentation layer between calls back and forth from your Down and Up methods.
That said, it appears that what you're trying to create is a cyclic animation through back and forth calls between your Up and Down methods via CATransaction's completionBlock. This seems an incredibly inefficient approach; why not try something more like:
-(void)scaleAndOpacityAnimations
{
CABasicAnimation *scaleAnimation = [CABasicAnimation animationWithKeyPath:#"transform.scale.xy”];
scaleAnimation.fromValue = #(0.7f);
scaleAnimation.toValue = #(1.0f);
CABasicAnimation *opacityAnimation = [CABasicAnimation animationWithKeyPath:#“opacity”];
opacityAnimation.fromValue = #(1.0f);
opacityAnimation.toValue = #(0.6f);
CAAnimationGroup *scaleAndOpacity = [CAAnimationGroup animation];
scaleAndOpacity.animations = #[scaleAnimation, opacityAnimation];
scaleAndOpacity.autoReverses = YES;
scaleAndOpacity.repeatCount = HUGE_VALF;
//OP had no value indicated for the duration in posted code, I’m including it here for completion
scaleAndOpacity.duration = 0.5f;
[self addAnimation:scaleAndOpacity forKey:#“pulse”];
}
Which will simply repeat infinitely many times without having to instantiate new CAAnimations on each cycle.