CAShapeLayer.isHidden automatically applying an animation in swift

Question

I'm new to CAShapeLayers so forgive me if this is an obvious fix. Im trying to move a line in sync with a UIScrollView when the view is moving up but keep the line still when the scroll view is moving down. I am using a delegate to detect when the scroll view is moving and this is my code for changing between the visible line.

func scrollViewDidScroll(_ scrollView: UIScrollView){
    if(mainScrollView.contentOffset.y < CGFloat(0.0)){
        topMainContentViewLine!.isHidden = false
        largeRocketImageView!.isHidden = true
        topViewLine!.isHidden = true
    }else if(mainScrollView.contentOffset.y == CGFloat(0)){
        topMainContentViewLine!.isHidden = false
        topViewLine!.isHidden = false
    }else{
        largeRocketImageView!.isHidden = false
        topMainContentViewLine!.isHidden = true
        topViewLine!.isHidden = false
    }
}

When I run my app I can easily see that the two lines are fading in and out instead of appearing and disappearing instantly. For comparison the image has no animation. Any ideas on how to get rid of the animation? Thanks again!

Answer 1

From the documentation:

https://developer.apple.com/documentation/quartzcore/calayer/1410838-ishidden

isHidden

A Boolean indicating whether the layer is displayed. Animatable.

See that word "animatable"? That is a rather tight shorthand; it means that when you set this property on a layer that is not the underlying backing layer of a UIView (e.g. any standalone sublayer), animation is the default. That's called implicit layer animation.

If you do not want animation of an animatable property under those circumstances, you can turn animation off by calling

CATransaction.setDisableActions(true)

You can do that either for a specific explicit transaction block (i.e. everything between matching begin() and commit() commands), or for the entire implicit transaction in which all your code runs.

More commonly, if you have a layer for which you always or mostly don't want animation, you'd host it as the underlying layer of a custom UIView. In that case, setting an animatable property would not animate, and if you needed animation, you would use an explicit CAAnimation (or UIView animation) to get it.

For comparison the image has no animation

Because largeRocketImageView is not, itself, a layer; it's a view.