如何居中alignmentSwift3.0 UICollectionView的单元格？
描述：
Objective-C和Swift2.0 ： 如何居中alignmentUICollectionView的单元格？
我通常会尝试将Swift2.0答案转换为Swift3.0解决scheme，但是方法如下：
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); }
似乎并不存在于Swift3.0 ，唯一的其他方法，我觉得有用的是：
func collectionView(_ collectionView: UICollectionView, transitionLayoutForOldLayout fromLayout: UICollectionViewLayout, newLayout toLayout: UICollectionViewLayout) -> UICollectionViewTransitionLayout { <#code#> }
但我不确定如何正确实施它。
题：
如何居中alignmentUICollectionView Swift3.0的单元格？
（iOS和tvOS的一个简单而通用的解决scheme将是完美的）
虽然rottenoats的答案很好，但它有一个额外的间距错误，并没有使用很多可用的swift 3语法。 我已经解决了这个问题，并减less了依赖到局部variables的数量。
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 }
NB：这个片段只能用于水平滚动，但可以很容易地进行调整。
这最终成为我使用的解决scheme。 阅读代码评论以获得更好的理解。 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 }
你正在寻找的方法在Swift 3有一个不同的签名。 新签名是这样的：
optional public func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets
PS：这个方法存在于UICollectionViewDelegateFlowLayout协议中。
希望这会有所帮助。
假设你符合UICollectionViewDelegateFlowLayout ，它应该是：
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) }
轻微的@rottenoats回答。 这是更通用的。
最重要的是记住要使你的视图控制器符合UICollectionViewDelegateFlowLayout协议。
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 }
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) }
而不是每次在您的委托方法中添加此代码，您可以添加自定义stream布局类到您的collectionView。 linkToSuchLayout