Objective-CSwift2.0我通常会尝试将
Swift2.0Swift3.0func 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
Swift3.0func collectionView(_ collectionView: UICollectionView, transitionLayoutForOldLayout fromLayout: UICollectionViewLayout, newLayout toLayout: UICollectionViewLayout) -> UICollectionViewTransitionLayout {
<#code#>
}
但我不确定如何正确实施。
如何将
UICollectionViewSwift3.0（针对 iOS 和 tvOS 的简单且通用的解决方案将是完美的）
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。 斯威夫特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
}
虽然 rottenoats 的答案很棒，但它有一个额外的间距错误，并且没有使用太多可用的 swift 3 语法。我已经修复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
}
注意：此代码片段仅适用于水平滚动，但可以轻松调整。
对@rottenoaats 答案进行轻微改编。这个比较通用。
最重要的是记住让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
}
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)
}
}
您正在寻找的方法在
Swift 3optional public func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets
P.S：此方法存在于
UICollectionViewDelegateFlowLayout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)
}
此代码应水平居中任何类型的集合视图，即使在 Swift 4.0 中存在额外项目：
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
}
}
不要忘记，如果您没有子类化
UICollectionViewControllerUICollectionViewDelegateFlowLayoutfunc 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)
}
您需要符合到
UICollectionViewDelegateFlowLayoutcollectionView(_:layout:insetForSectionAt:)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);
}
}
使用此解决方案进行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)
我认为，如果您的 collectionView 有一行，最简单的解决方案是将其替换为滚动视图内的 stackView，以便您可以设置视图之间所需的间距。 此外，如果您想要一些填充，您可以应用它。
我的细胞大小是动态的并且不同，因此rottenoats的答案对我不起作用。这就是我最终的做法：
public override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
calculateAndSetCollectionInsets()
}
private func calculateAndSetCollectionInsets() {
let padding = (collectionView.frame.width - collectionView.contentSize.width) / 2
guard padding > .zero else {
itemFilterCollectionView.contentInset = .zero
return
}
collectionView.contentInset = UIEdgeInsets(horizontal: padding, vertical: 0)
}