Is CABasicAnimation practice different for UI objects and CALayers? - ios

Question

I was just wondering if this is the correct way to animate a CALayer with a CABasicAnimation.
On Stack Overflow I have been taught how to animate UI objects by setting a new position before running a CABasicAnimation:
Animating a UI Object Example
gameTypeControl.center = CGPointMake(gameTypeControl.center.x, -slidingUpValue/2);
CABasicAnimation *removeGameTypeControl = [CABasicAnimation animationWithKeyPath:#"transform.translation.y"];
[removeGameTypeControl setFromValue:[NSNumber numberWithFloat:slidingUpValue]];
[removeGameTypeControl setToValue:[NSNumber numberWithFloat:0]];
[removeGameTypeControl setDuration:1.0];
[removeGameTypeControl setTimingFunction:[CAMediaTimingFunction functionWithControlPoints:0.8 :-0.8 :1.0 :1.0]];
[[gameTypeControl layer] addAnimation:removeGameTypeControl forKey:#"removeGameTypeControl"];
Now I've been tried this method on a CALayer but it seems to work differently. For me to get the same result. I have the set the ToValue to the new y position instead of using the value 0 like I've done with my UI object animations.
Animating a CALayer Example
serveBlock2.position = CGPointMake((screenBounds.size.height/4)*3, -screenBounds.size.width/2);
CABasicAnimation *updateCurrentServe2 = [CABasicAnimation animationWithKeyPath:#"position.y"];
updateCurrentServe2.fromValue = [NSNumber numberWithFloat:slidingUpValue/2];
[updateCurrentServe2 setToValue:[NSNumber numberWithFloat:-screenBounds.size.width/2]];
[updateCurrentServe2 setDuration:1.0];
[serveBlock2 addAnimation:updateCurrentServe2 forKey:#"serveBlock2 updateCurrentServe2"];
Is this correct? Am I doing this right?

Answer 1

The problem is that if serveBlock2 is not a view's immediately underlying layer, setting its position, as you do in the first line of the second example, starts a different animation (an implicit animation). The way to prevent that is by turning off implicit animations. Thus this example from my book:
CompassLayer* c = (CompassLayer*)self.compass.layer;
[CATransaction setDisableActions:YES]; // <=== this is important
c.arrow.transform = CATransform3DRotate(c.arrow.transform, M_PI/4.0, 0, 0, 1);
CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:#"transform"];
anim.duration = 0.8;
[c.arrow addAnimation:anim forKey:nil];
That way, I don't have to have a fromValue or a toValue! The old value and the new value are known automatically from the presentation layer and the model layer.