Shadows will not animate and ignore code state changes

[destefanis]

I'm attempting to animate a box shadow on a progress bar to glow upon completion. However, all of my attempts to animate the shadow properties have not worked.

The only solution I've found is a binary on/off if the layer already has a shadow set.

I've also attempted:

• Creating shadows on each state and changing properties on state animation change (for instance changing blur, spread, color etc) these never change and I don't know why.
• Creating shadow layers that I could change the opacity of to create a quick pulse animation. However changing the opacity of these layers does nothing in code, even set at 0 opacity they are still visible, oddly transforms work which is confusing.
• Setting a base default shadow on a layer, then updating the shadow in another state.

From what I've explored in the docs this topic is not covered (I could have missed it but I've been tryin g for some time).

Is there something I'm missing or can shadows not be animated?

Thanks!