iphone - UICollectionView and Custom Height -

i'm using uiviewcontroller inside uicollectionvieww, , searched on internet how can customize height of total uicollectionview. setup uicollectionview height >= 1 (i'm using autolayout) in .m file tried with:

uicollectionviewflowlayout *flowlayout = [[uicollectionviewflowlayout alloc] init]; [flowlayout setitemsize:cgsizemake(160, 160)]; [flowlayout setscrolldirection:uicollectionviewscrolldirectionvertical]; [flowlayout setminimuminteritemspacing:0]; [flowlayout setminimumlinespacing:0]; nsinteger itemcount = [self.collectionview numberofitemsinsection:0]; [flowlayout setitemsize:cgsizemake(self.collectionview.frame.size.width, 160 * itemcount)]; [self.collectionview setcollectionviewlayout:flowlayout]; nslog(@"%f", self.collectionview.frame.size.height); 

but in nslog still show me height 1...how can setup height of uicollectionview custom height(that based on element in section * 160). suggest ? thanks.

edit: create cells:

-(uicollectionviewcell *)collectionview:(uicollectionview *)collectionview cellforitematindexpath:(nsindexpath *)indexpath {     gallerycell *cell = (gallerycell *)[collectionview dequeuereusablecellwithreuseidentifier:@"gallerycell" forindexpath:indexpath];       nsdictionary *photo = [self.beachimages objectatindex:indexpath.row];     [cell.imageview setimagewithurl:[nsurl urlwithstring:[nsstring stringwithformat:@"%@", [photo objectforkey:@"original_url"]]] placeholderimage:[uiimage imagenamed:@"avatar-placeholder.png"]];       return cell;  } 

edit: maybe problem use autolayout ? here constraints: http://cl.ly/image/2l0m432w0u1v edit: tried adding constraint code:

[self.collectionview removeconstraints:self.collectionview.constraints];     nslayoutconstraint *con1 = [nslayoutconstraint constraintwithitem:self.collectionview attribute:nslayoutattributeheight relatedby:0 toitem:nil attribute:nslayoutattributenotanattribute multiplier:1  constant:320];     [self.collectionview addconstraints:@[con1]]; 

but not show cells...