CABasicAnimation flicker when applying the completion - ios

Question

I am trying to apply a rotation animation by number of degrees to a UIImageView and persist the rotation transformation in the completion block.
The problem that I am facing is that when the completion block is executed there is a visible flicker generated by passing from the end state of the animation to the completion block.
Here is the code that I am currently using:
if (futureAngle == currentAngle) {
return;
}
float rotationAngle;
if (futureAngle < currentAngle) {
rotationAngle = futureAngle - currentAngle;
}else{
rotationAngle = futureAngle - currentAngle;
}
float animationDuration = fabs(rotationAngle) / 100;
rotationAngle = GLKMathDegreesToRadians(rotationAngle);
[CATransaction begin];
CABasicAnimation *rotationAnimation;
rotationAnimation = [CABasicAnimation animationWithKeyPath:#"transform.rotation.z"];
rotationAnimation.byValue = [NSNumber numberWithFloat:rotationAngle];
rotationAnimation.duration = animationDuration;
rotationAnimation.removedOnCompletion = YES;
[CATransaction setCompletionBlock:^{
view.transform = CGAffineTransformRotate(view.transform, rotationAngle);
}];
[view.layer addAnimation:rotationAnimation forKey:#"rotationAnimation"];
[CATransaction commit];

Answer 1

When you say flicker, I assume you mean that at the end of the animation, that it momentarily returns to the initial state before returning back to the final state? This can be solved either by
setting the final view.transform before you start the animation (and you no longer need the completionBlock);
by setting the animation's fillMode to kCAFillModeForwards and set removedOnCompletion to false.
Personally, I think setting the animated property to its destination value before you start the animation is the easiest way to do this.
Thus:
- (void)rotate:(UIView *)view by:(CGFloat)delta {
float animationDuration = 2.0;
CGFloat currentAngle = self.angle; // retrieve saved angle
CGFloat nextAngle = self.angle + delta; // increment it
self.angle = nextAngle; // save new value
view.transform = CGAffineTransformMakeRotation(nextAngle); // set property to destination rotation
CABasicAnimation *rotationAnimation;
rotationAnimation = [CABasicAnimation animationWithKeyPath:#"transform.rotation.z"]; // now rotate
rotationAnimation.fromValue = #(currentAngle);
rotationAnimation.toValue = #(nextAngle);
rotationAnimation.duration = animationDuration;
rotationAnimation.removedOnCompletion = YES;
[view.layer addAnimation:rotationAnimation forKey:#"rotationAnimation"];
}
Or, I think even easier, just adjust the transform:
- (void)rotate:(UIView *)view by:(CGFloat)delta {
float animationDuration = 2.0;
CGAffineTransform transform = view.transform; // retrieve current transform
CGAffineTransform nextTransform = CGAffineTransformRotate(transform, delta); // increment it
view.transform = nextTransform; // set property to destination rotation
CABasicAnimation *rotationAnimation;
rotationAnimation = [CABasicAnimation animationWithKeyPath:#"transform"]; // now rotate
rotationAnimation.fromValue = [NSValue valueWithCGAffineTransform:transform];
rotationAnimation.toValue = [NSValue valueWithCGAffineTransform:nextTransform];
rotationAnimation.duration = animationDuration;
rotationAnimation.removedOnCompletion = YES;
[view.layer addAnimation:rotationAnimation forKey:#"rotationAnimation"];
}

Answer 2

I was seeing flickering even when using the suggested answer from Rob, but turns out it seems to just be a simulator bug. On real devices I dont see the flicker, if you have only been testing on simulator, try on a real device unless you want to waste hours of your life potentially like myself.