ios - Why is reloadData() not working in my app? -

i'm trying download set of images parse.com uicollectionview. works except reloaddata() function. in app, can hit button , re-enter uicollectionview , of images there. don't know i'm doing wrong reloaddata() function.

var images = [uiimage]() var imagefiles = [pffile]()  class collectioncollectionviewcontroller: uiviewcontroller, uicollectionviewdelegate, uicollectionviewdatasource {  @ibaction func xy1button(sender: anyobject) {  }  @ibaction func xy2button(sender: anyobject) {          var downloadimages = pfquery(classname: "xy2")         downloadimages.wherekey("expansion", equalto: "xy2")         downloadimages.findobjectsinbackgroundwithblock {             (objects: [anyobject]?, error: nserror?) -> void in             if error == nil {                 println("successfully retrieved \(objects!.count) cards.")                 if let objects = objects as? [pfobject] {                     object in objects {                         imagefiles.append(object["image"] as! pffile)                         dispatch_async(dispatch_get_main_queue() ^{                             self.collectionview.reloaddata()                             });                         //error breakpoint here:'thread 1: exc_bad_instruction (code=exc_i386_invop, subcode=0x0)'                     }                 }             } else {                 println("error: \(error!) \(error!.userinfo!)")             }           } }    override func viewdidload() {     super.viewdidload()   }  func collectionview(collectionview: uicollectionview, numberofitemsinsection section: int) -> int {     return imagefiles.count }  func collectionview(collectionview: uicollectionview, cellforitematindexpath indexpath: nsindexpath) -> uicollectionviewcell {      let cell: cardscollectionviewcell = collectionview.dequeuereusablecellwithreuseidentifier("cell", forindexpath: indexpath) as! cardscollectionviewcell     //cell.cardsimg.image = uiimage(named: cards[indexpath.row] string)     //return cell     imagefiles[indexpath.row].getdatainbackgroundwithblock{         (imagedata: nsdata?, error: nserror?) -> void in          if error == nil {              let image = uiimage(data: imagedata!)              cell.cardsimg.image = image         }       }     return cell } } 

the reloaddata need executed in main thread update ui. can try

dispatch_async(dispatch_get_main_queue(), ^{             self.collectionview.reloaddata() });  

and @grimxn suggested, should check if collectionview iboutlet connected in storyboard or xib file.