How to center align the cells of a UICollectionView in Swift3.0?

Question

Description:

Answer for Objective-C and Swift2.0: How to center align the cells of a UICollectionView?

I usually would try to conver

Answer 1

This ended up being the solution I used. Read the code comments for a better understanding. Swift 5

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

    //Where elements_count is the count of all your items in that
    //Collection view...
    let cellCount = CGFloat(elements_count)

    //If the cell count is zero, there is no point in calculating anything.
    if cellCount > 0 {
        let flowLayout = collectionViewLayout as! UICollectionViewFlowLayout
        let cellWidth = flowLayout.itemSize.width + flowLayout.minimumInteritemSpacing

        //20.00 was just extra spacing I wanted to add to my cell.
        let totalCellWidth = cellWidth*cellCount + 20.00 * (cellCount-1)
        let contentWidth = collectionView.frame.size.width - collectionView.contentInset.left - collectionView.contentInset.right

        if (totalCellWidth < contentWidth) {
            //If the number of cells that exists take up less room than the
            //collection view width... then there is an actual point to centering them.

            //Calculate the right amount of padding to center the cells.
            let padding = (contentWidth - totalCellWidth) / 2.0
            return UIEdgeInsets(top: 0, left: padding, bottom: 0, right: padding)
        } else {
            //Pretty much if the number of cells that exist take up
            //more room than the actual collectionView width, there is no
            // point in trying to center them. So we leave the default behavior.
            return UIEdgeInsets(top: 0, left: 40, bottom: 0, right: 40)
        }
    }
    return UIEdgeInsets.zero
}

Answer 2

Here's a recent solution, works for Swift 5.0

extension YourViewController: UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView,
                        layout collectionViewLayout: UICollectionViewLayout,
                        insetForSectionAt section: Int) -> UIEdgeInsets {
        let itemWidth = 80
        let spacingWidth = 4
        let numberOfItems = collectionView.numberOfItems(inSection: section)
        let cellSpacingWidth = numberOfItem * spacingWidth
        let totalCellWidth = numberOfItems * itemWidth + cellSpacingWidth
        let inset = (collectionView.layer.frame.size.width - CGFloat(totalCellWidth)) / 2
        return UIEdgeInsets(top: 5, left: inset, bottom: 5, right: inset)
    }
}

Answer 3

Assuming that you are conforming to UICollectionViewDelegateFlowLayout, it should be:

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
    let edgeInsets = (screenWight - (CGFloat(elements.count) * 50) - (CGFloat(elements.count) * 10)) / 2
    return UIEdgeInsets(top: 0, left: edgeInsets, bottom: 0, right: 0)
}

Answer 4

The method that you are looking for is present with a different signature in Swift 3. The new signature is this:

optional public func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets

P.S: This method is present in UICollectionViewDelegateFlowLayout protocol.
Hope this would help.

Answer 5

I think the easiest solution in case your collectionView has one row is to substitute it by a stackView inside a scrollview so you can set the spacing you want between the views. Besides, if you want some padding you will be able apply it.

Answer 6

Slight adaptation of @rottenoats answer. This is more generic.

Most importantly remember to make your view controller conform to the UICollectionViewDelegateFlowLayout protocol.

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

    guard let flowLayout = collectionViewLayout as? UICollectionViewFlowLayout else {
        return .zero
    }

    let cellCount = CGFloat(collectionView.numberOfItems(inSection: section))

    if cellCount > 0 {
        let cellWidth = flowLayout.itemSize.width + flowLayout.minimumInteritemSpacing

        let totalCellWidth = cellWidth * cellCount
        let contentWidth = collectionView.frame.size.width - collectionView.contentInset.left - collectionView.contentInset.right - flowLayout.headerReferenceSize.width - flowLayout.footerReferenceSize.width

        if (totalCellWidth < contentWidth) {
            let padding = (contentWidth - totalCellWidth + flowLayout.minimumInteritemSpacing) / 2.0
            return UIEdgeInsetsMake(0, padding, 0, 0)
        }
    }

    return .zero
}