         collectionView!.userInteractionEnabled = true
     }
     
-    private func calculate() {
+    private func calculate() -> Bool {
         
         // retrieve item distance
         self.itemSpace = cgfloat(self.dataSource?.swipeViewItemDistance?(self), defaultValue: 0)

        } else {
            contentSize.width = ceil((itemSize.width + itemSpace) * CGFloat(itemCount + dummyCount * 2) - itemSpace)
        }
        collectionView!.contentSize = contentSize
        log("successfully set content size: \(self.collectionView!.contentSize)")
    }
}


        log("\(#function)")
        
        initialized = false
        
        // calculate for view presentation
        if calculate() {
            if let itemSize = self.itemSize {
                collectionView!.size = CGSizeMake(self.width, itemSize.height)
            }
        }
        
