ios - Where do I update my constraint before the view is on screen? -

i need update nslayoutconstraints before view comes on screen depending on device's screen size.

what want update becomes invisible user's eyes. , not know can because : - if in :

- (void)viewwilllayoutsubviews

of uiviewcontroller called twice make twice calculation on constraint , not want set bool or counter... - if in :

- (void)viewdidload

it not work because calculate constrain's value based on view of view controller 0 height @ moment.

i see there lot of methods auto layout (setneedsupdate ...) , if tell me best way achieve update of constraints once in viewcontroller lifecycle great.

thanks help! (n.b: auto-layout concept new me.)

try overriding updateviewconstraints on view controller. (don't forget call super ;) )

see apple docs here