ios - UICollectionView size: iOS9 vs. iOS8 -

in app want compute best cell height cells match visible area.

what best way size of visible rect? mean space between navigationbar , bottom of screen.

currently size

self.collectionview!.frame.size 

but contains area of statusbar , navigationbar. substract size of nav- , stautusbar. works ios9, not on ios8.

so, how visible area devices?

not answer, workaround, detect ios version , apply modifications according it:

if ( ([[[uidevice currentdevice] systemversion] compare:@"9.0" options:nsnumericsearch] != nsorderedascending) ) { /* ios 9.0 or greater */ }

of course, better define layouts using constraints relative top layout guide (ideally using opaque navigation bar) avoid messing that, or add 20 points top constraints when detecting ios versions.