In the context of constraint animation, I would like to mention a specific situation where I animated a constraint immediately within a keyboard_opened notification.
Constraint defined a top space from a textfield to top of the container. Upon keyboard opening, I just divide the constant by 2.
I was unable to achieve a conistent smooth constraint animation directly within the keyboard notification. About half the times view would just jump to its new position - without animating.
It occured to me there might be some additional layouting happening as result of keyboard opening. Adding a simple dispatch_after block with a 10ms delay made the animation run every time - no jumping.