Question

说明

回答Objective-C和Swift2.0：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，但方法是：

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);
    }

似乎不存在于Swift3.0中，而我发现的唯一有用的其他方法似乎是：

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

但我不确定如何正确实施它。

问题：

如何将UICollectionView中Swift3.0的单元格对齐？

（iOS和tvOS的简单通用解决方案将是完美的）

Answer 1

虽然rottenoats答案很好，但它有一个额外的间距错误，并没有使用大部分可用的swift 3语法。我已经解决了这个问题并减少了对局部变量的依赖数量。

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

    // Make sure that the number of items is worth the computing effort.
    guard let flowLayout = collectionViewLayout as? UICollectionViewFlowLayout,
        let dataSourceCount = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: section),
        dataSourceCount > 0 else {
            return .zero
    }


    let cellCount = CGFloat(dataSourceCount)
    let itemSpacing = flowLayout.minimumInteritemSpacing
    let cellWidth = flowLayout.itemSize.width + itemSpacing
    var insets = flowLayout.sectionInset


    // Make sure to remove the last item spacing or it will
    // miscalculate the actual total width.
    let totalCellWidth = (cellWidth * cellCount) - itemSpacing
    let contentWidth = collectionView.frame.size.width - collectionView.contentInset.left - collectionView.contentInset.right


    // If the number of cells that exist take up less room than the
    // collection view width, then center the content with the appropriate insets.
    // Otherwise return the default layout inset.
    guard totalCellWidth < contentWidth else {
        return insets
    }


    // Calculate the right amount of padding to center the cells.
    let padding = (contentWidth - totalCellWidth) / 2.0
    insets.left = padding
    insets.right = padding
    return insets
}

N.B。：此代码段仅适用于水平滚动，但可以轻松调整。

Answer 2

这最终成为我使用的解决方案。阅读代码注释以便更好地理解。 Swift 3.0

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 UIEdgeInsetsMake(0, padding, 0, 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 UIEdgeInsetsMake(0, 40, 0, 40)
            }
        }

        return UIEdgeInsets.zero
    }

Answer 3

@rottenoats答案的轻微改编。这更通用。

最重要的是要记住让你的视图控制器符合UICollectionViewDelegateFlowLayout协议。

LinearLayout

Answer 4

您要查找的方法在Swift 3中显示不同的签名。新的签名是：

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

P.S：此方法存在于UICollectionViewDelegateFlowLayout协议中希望这会有所帮助。

Answer 5

假设您符合UICollectionViewDelegateFlowLayout，那应该是：

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 6

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

let allCellWidth = KcellWidth * numberOfCell
let cellSpacingWidth = CellSpacing * (numberOfCell - 1)

let leftInset = (collectionViewWidth - CGFloat(allCellWidth + cellSpacingWidth)) / 2
let rightInset = leftInset

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

Answer 7

这是最近的解决方案，适用于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 8

您需要符合以遵守UICollectionViewDelegateFlowLayout协议，以找到collectionView(_:layout:insetForSectionAt:)方法，该方法已在此处定义。以下实现在swift 4中用于水平collectionView很好

extension YourViewController: UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        let cellWidth = CGFloat(integerLiteral: YourCellsWidth)
        let count = self.YourCollectionViewDataSource.count
        let top = CGFloat(integerLiteral: 0)    // I don't need to set top and bottom spacing
        let cellsAccumulatedWidth = CGFloat(integerLiteral: count) * cellWidth
        let cellsSpacingAccumulatedWidth = CGFloat(integerLiteral: (count - 1) * 5)
        let left = (self.collectionView.frame.size.width - cellsAccumulatedWidth - cellsSpacingAccumulatedWidth) / 2
        let bottom = top
        let right = left

        return UIEdgeInsetsMake(top, left, bottom, right);
    }
}

Answer 9

即使在 Swift 4.0 中有额外的项目，此代码也应将任何类型的集合视图水平居中放置：

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
    let flowLayout = collectionViewLayout as! UICollectionViewFlowLayout
    let cellWidth: CGFloat = flowLayout.itemSize.width
    let cellSpacing: CGFloat = flowLayout.minimumInteritemSpacing
    let cellCount = CGFloat(collectionView.numberOfItems(inSection: section))
    var collectionWidth = collectionView.frame.size.width
    if #available(iOS 11.0, *) {
        collectionWidth -= collectionView.safeAreaInsets.left + collectionView.safeAreaInsets.right
    }
    let totalWidth = cellWidth * cellCount + cellSpacing * (cellCount - 1)
    if totalWidth <= collectionWidth {
        let edgeInset = (collectionWidth - totalWidth) / 2
        return UIEdgeInsetsMake(flowLayout.sectionInset.top, edgeInset, flowLayout.sectionInset.bottom, edgeInset)
    } else {
        return flowLayout.sectionInset
    }
}

别忘了您是否不是UICollectionViewController的子类，请确保您的类符合UICollectionViewDelegateFlowLayout协议

Answer 10

将此解决方案用于中心对齐的水平滚动。

let totalCellWidth = Int(collectionView.frame.height * CGFloat(numberOfItems()))

        // if total width is greater than collection's width, then no need to align center
        if totalCellWidth > Int(collectionView.frame.width) {
            return UIEdgeInsets.zero
        }

        let totalSpacingWidth = cellSpacing * (numberOfItems() - 1)
        let leftInset = (collectionView.frame.width - CGFloat(totalCellWidth + totalSpacingWidth)) / 2
        let rightInset = leftInset
        return UIEdgeInsets(top: 0, left: leftInset, bottom: 0, right: rightInset)

Answer 11

我认为，如果您的collectionView有一行，最简单的解决方案是在滚动视图内部用stackView替代它，以便您可以设置视图之间的间距。此外，如果您需要填充，可以使用它。

如何在Swift3.0中居中对齐UICollectionView的单元格？

说明

问题：

11 个答案: