             let columnIndex  = self.longestColumnIndex()
             top = CGFloat(self.columnHeights.objectAtIndex(columnIndex).floatValue) - minimumInteritemSpacing + sectionInset.bottom
     
-            if let height = self.delegate?.colletionView?(self.collectionView, layout: self, heightForFooterInSection: section){
+            if let height = self.delegate?.colletionView?(self.collectionView!, layout: self, heightForFooterInSection: section){
                 footerHeight = height
             }else{
                 footerHeight = self.footerHeight

            * 1. Get section-specific metrics (minimumInteritemSpacing, sectionInset)
            */
            var minimumInteritemSpacing : CGFloat
            if let miniumSpaceing = self.delegate?.colletionView?(self.collectionView, layout: self, minimumInteritemSpacingForSectionAtIndex: section){
                minimumInteritemSpacing = miniumSpaceing
            }else{
                minimumInteritemSpacing = self.minimumColumnSpacing
            }
            
            var sectionInsets :  UIEdgeInsets
            if let insets = self.delegate?.colletionView?(self.collectionView, layout: self, insetForSectionAtIndex: section){
                sectionInsets = insets
            }else{
                sectionInsets = self.sectionInset
            }
            
            let width = self.collectionView.frame.size.width - sectionInset.left - sectionInset.right
            let spaceColumCount = CGFloat(self.columnCount-1)
            let itemWidth = floor((width - (spaceColumCount*self.minimumColumnSpacing)) / CGFloat(self.columnCount))
            

    
    func itemWidthInSectionAtIndex (section : NSInteger) -> CGFloat {
        var insets : UIEdgeInsets
        if let sectionInsets = self.delegate?.colletionView?(self.collectionView!, layout: self, insetForSectionAtIndex: section){
            insets = sectionInsets
        }else{
            insets = self.sectionInset
        }
        let width:CGFloat = self.collectionView!.frame.size.width - sectionInset.left-sectionInset.right
        let spaceColumCount:CGFloat = CGFloat(self.columnCount-1)
        return floor((width - (spaceColumCount*self.minimumColumnSpacing)) / CGFloat(self.columnCount))
    }
