ios - How to force a UIView to update -

i working on application downloading json data server, , displays on uiview. view updated, takes 15 seconds. have tested make sure not download delaying update, , if change view's background color adding data waits update. correct in thinking view not updating, or else? how force view update? thanks.

var newview = customview(product: products[0],descriptive: false)         contentview.addsubview(newview)          let backheight = nslayoutconstraint(item: newview, attribute: nslayoutattribute.height, relatedby: nslayoutrelation.equal, toitem: view, attribute: nslayoutattribute.height, multiplier: 0.2, constant: 0)         let backwidth = nslayoutconstraint(item: newview, attribute: nslayoutattribute.width, relatedby: nslayoutrelation.equal, toitem: contentview, attribute: nslayoutattribute.width, multiplier: 1, constant: 0)          let backxposition = nslayoutconstraint(item: newview, attribute: nslayoutattribute.left, relatedby: nslayoutrelation.equal, toitem: contentview, attribute: nslayoutattribute.left, multiplier: 1, constant:0 )         let backyposition = nslayoutconstraint(item: newview, attribute: nslayoutattribute.top, relatedby: nslayoutrelation.equal, toitem: colorlabel, attribute: nslayoutattribute.bottom, multiplier: 1.0, constant: 0)         view.addconstraints([backheight,backwidth,backxposition,backyposition]) 

this how adding items view.

when got data server can update ui view main queue shown in below code:

dispatch_async(dispatch_get_main_queue()) {     //update ui here  }