борзый ошибка - использование незаявленных типа "ячейки" - посмотреть коллекцию

совершенно новой для программирования в swift, в чем причина моей ошибки и как я могу это исправить? большое спасибо.

import uikitimport photosclass photosviewcontroller: uiviewcontroller, uicollectionviewdelegate, uicollectionviewdatasource , uicollectionviewdelegateflowlayout, uiimagepickercontrollerdelegate, uinavigationcontrollerdelegate{    @iboutlet weak var mycollectionview: uicollectionview!    var imagesarray = [uiimage]()    override func viewdidload(){        super.viewdidload()        mycollectionview.delegate = self        mycollectionview.datasource = self    }    @ibaction func addphoto(_ sender: anyobject) {        let picker:uiimagepickercontroller = uiimagepickercontroller()        picker.sourcetype = .photolibrary        picker.mediatypes = uiimagepickercontroller.availablemediatypes(for: .photolibrary)!        picker.delegate = self        picker.allowsediting = false        self.present(picker, animated: true, completion: nil)    }    func collectionview(_ collectionview: uicollectionview, cellforitemat indexpath: indexpath) -> uicollectionviewcell {        let cell = collectionview.dequeuereusablecellwithreuseidentifier("cell", forindexpath: indexpath) as! cell        cell.configurecell(imagesarray[indexpath.row])        return cell    }    func collectionview(_ collectionview: uicollectionview, numberofitemsinsection section: int) -> int {        return imagesarray.count    }    func imagepickercontroller(_ picker: uiimagepickercontroller, didfinishpickingmediawithinfo info: [string : any]) {        if let pickedimage = (info[uiimagepickercontrolleroriginalimage] as? uiimage){            imagesarray = [pickedimage,pickedimage,pickedimage]//will store three selected images in your array            mycollectionview.reloaddata()        }        dismiss(animated: true, completion: nil)    }}