ios - 如何在 Swift3.0 中居中对齐 UICollectionView 的单元格？

Question

描述:

Objective-C 和 Swift2.0 的答案:How to center align the cells of a UICollectionView?

我通常会尝试将 Swift2.0 答案转换为 Swift3.0 解决方案，但是方法:

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {
        let edgeInsets = (screenWight - (CGFloat(elements.count) * 50) - (CGFloat(elements.count) * 10)) / 2
        return UIEdgeInsetsMake(0, edgeInsets, 0, 0);
    }

在 Swift3.0 中似乎不存在，我发现唯一有用的其他方法是:

func collectionView(_ collectionView: UICollectionView, transitionLayoutForOldLayout fromLayout: UICollectionViewLayout, newLayout toLayout: UICollectionViewLayout) -> UICollectionViewTransitionLayout {
        <#code#>
}

但我不确定如何正确实现它。

问题:

如何在 Swift3.0 中居中对齐 UICollectionView 的单元格？

(适用于 iOS 和 tvOS 的简单通用解决方案将是完美的)

Answer 1

这最终成为我使用的解决方案。阅读代码注释以获得更好的理解。 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
}