swift - NSCollectionView dataSource not working properly -

i'm experimenting new nscollectionview api, introduced in el capitan.

following wwdc video, create subclass of nscollectionviewflowlayout determine layout of collection view.

class layout : nscollectionviewflowlayout {    override func preparelayout() {      super.preparelayout()      self.minimuminteritemspacing = 0     self.minimumlinespacing = 0      let cheight = self.collectionview!.bounds.height     let cwidth = self.collectionview!.bounds.width      self.itemsize = cgsizemake(cwidth / 2.0, cheight / 6.0)    }  } 

after that, i've created nsobject subclass serve data source.

class datasource : nsobject, nscollectionviewdatasource {    func collectionview(collectionview: nscollectionview, numberofitemsinsection section: int) -> int {     return 5   }    func collectionview(collectionview: nscollectionview, itemforrepresentedobjectatindexpath indexpath: nsindexpath) -> nscollectionviewitem {      /* doesn't called! */      let item = collectionview.makeitemwithidentifier("cell", forindexpath: indexpath)      item.view.wantslayer = true     item.view.layer?.backgroundcolor = nscolor.redcolor().cgcolor      return item    }  } 

the issue collectionview:itemforrepresentedobjectatindexpath: never gets called.

this how initialise collection view:

let collectionview = nscollectionview(frame: view.bounds)  let datasource = datasource() let layout = layout()  collectionview.collectionviewlayout = layout collectionview.registerclass(nscollectionviewitem.self,                                   foritemwithidentifier: "cell") collectionview.datasource = datasource  collectionview.backgroundcolors = [.blackcolor()] 

i can see collection view in superview, there no cells.

also, line, if called outside delegate (but after cell class registered) makes app crash!

let item = collectionview.makeitemwithidentifier("cell", forindexpath: /*any index path*/) 

am doing wrong or nscollectionview new api broken?

thanks.

the method makeitemwithidentifier crucial , looks .xib named "cell" in bundle: may need register registernib:foritemwithidentifier: if comes bundle.

thus problem comes before that, since collectionview:itemforrepresentedobjectatindexpath never gets called , arise pattern: why create new class serve datasource , not use same nsviewcontroller nscollectionview resides?

i , new api works perfectly. hope you!