Swift-集合视图-集合视图中间的中心单元格

Question

I am trying to centre all the cells inside a UICollectionView in its middle. The cells are divided as 11x4.

I have tried using the code below however, the cells are grouped in one line.

What I am trying to achieve is shown in the second image:

WRONG

SHOULD BE

override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {

        let letterCell = collectionView.dequeueReusableCellWithReuseIdentifier("letterCell", forIndexPath: indexPath) as! LetterCellView

        letterCell.center.y = self.view.center.y

        return letterCell

    }

Also in my code I amusing collectionViewLayout to divide the cells in 4 lines, maybe I should implement the centering system in here but I cannot get how to achieve this. Any Idea?:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {

        let totalCellWidth = 30 * 11
        let totalSpacingWidth = 2 * (11 - 1)

        let leftInset = (self.view.frame.size.width - CGFloat(totalCellWidth + totalSpacingWidth)) / 2;
        let rightInset = leftInset

        return UIEdgeInsetsMake(0, leftInset, 0, rightInset)
    }

Answer 1

if you prefer a more visual approach try changing the insets

Answer 2

Found out the Solution:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {

        let totalCellWidth = 30 * 11
        let totalSpacingWidth = 2 * (11 - 1)

        let leftInset = (self.view.frame.size.width - CGFloat(totalCellWidth + totalSpacingWidth)) / 2;
        let rightInset = leftInset

        let totalCellHeight = 30 * 4
        let totalSpacingHeight = 5 * (4 - 1)

        let topInset = (self.view.frame.size.height - CGFloat(totalCellHeight + totalSpacingHeight)) / 2;
        let bottInset = topInset

        return UIEdgeInsetsMake(topInset, leftInset, bottInset, rightInset)
    }