Animating a group of UIView subviews continuously - ios

Question

I am trying to show the movement of a vehicle on a road in my app. For this I am keeping my vehicle stationary and moving the lanes in the road from top to bottom continuously to create the effect. The lanes are added as subview to roadView and I am trying to animate all the subviews in the roadView as seen in the code below.
The problem I am facing is that the lane nearest to the bottom is moving at a faster speed compared the one at the top in the beginning although I am calculating the duration based on constant speed.
-(void)animateLanes {
for (UIView *laneView in [self.roadView subviews]) {
if (laneView.tag < 10) {
float distance = self.view.frame.size.height - CGRectGetMaxY(laneView.frame);
float duration = distance/10;
[UIView animateWithDuration:duration animations:^{
laneView.frame = CGRectMake(laneView.frame.origin.x, self.view.frame.size.height+laneView.frame.size.height, laneView.frame.size.width, laneView.frame.size.height);
} completion:^(BOOL finished) {
laneView.frame = CGRectMake(self.roadView.frame.size.width/2 - 10, -laneView.frame.size.height, 20, 40);
[self nextStep:laneView];
}];
}
}
}
-(void) nextStep:(UIView *) laneView{
float distance = self.view.frame.size.height - CGRectGetMaxY(laneView.frame);
float duration = distance/10;
[UIView animateWithDuration:duration delay:0 options:UIViewAnimationOptionRepeat animations:^{
laneView.frame = CGRectMake(laneView.frame.origin.x, self.view.frame.size.height+laneView.frame.size.height, laneView.frame.size.width, laneView.frame.size.height);
} completion:^(BOOL finished) {
laneView.frame = CGRectMake(self.roadView.frame.size.width/2 - 10, -laneView.frame.size.height, 20, 40);
}];
}

Answer 1

I would most definitely look into SpriteKit for this kind of thing. The update loop in its SKScene will allow you to make sure everything is running smoothly.
However, if you do do this, you don't have to make all these UIView Animation calls. Do this:
//calculate duration and distance first, then:
[UIView animateWithDuration:duration animations:^{
for (UIView *laneView in [self.roadView subviews]) {
laneView.frame = CGRectMake(laneView.frame.origin.x, self.view.frame.size.height+laneView.frame.size.height, laneView.frame.size.width, laneView.frame.size.height);
}
} completion:^(BOOL finished) {
for (UIView *laneView in [self.roadView subviews]) {
laneView.frame = CGRectMake(self.roadView.frame.size.width/2 - 10, -laneView.frame.size.height, 20, 40);
[self nextStep:laneView];
}
}];
Although I do NOT advise doing any of this at all. Use a game library, namely SpriteKit because of its ease of integration and simplicity.

Answer 2

SpriteKit makes a lot more sense for this type of task, IMO. The logic would be similar and the objects would belong to SKScene instance which has a handy update method perfect for the loop effect you're aiming for.