Subview frame is incorrect when creating UICollectionViewCell

You can get the final frames of your cell by overriding layoutIfNeeded() in your custom Cell class like this:

override func layoutIfNeeded() {
    super.layoutIfNeeded()
    self.subView.layer.cornerRadius = self.subView.bounds.width / 2
}

then in your UICollectionView data Source method cellForRowAtIndexPath: do this:

let cell = collectionView.dequeueReusableCellWithReuseIdentifier("Cell", forIndexPath: indexPath) as! CustomCollectionViewCell
cell.setNeedsLayout()
cell.layoutIfNeeded()