创建一个具有反向流布局的UICollectionView
创建一个具有反向流布局的UICollectionView
提问于 2017-11-29 21:25:43
我想要创建一个类似聊天视图的视图，其中最新的消息出现在屏幕底部。我希望UICollectionViewCells被“固定”在屏幕底部--与默认的流布局相反。我该怎么做？
我从另一个堆栈溢出回答中获得了这段代码，但它不适用于可变高度项(它需要这样做)：
import Foundation
import UIKit
class InvertedStackLayout: UICollectionViewLayout {
let cellHeight: CGFloat = 100 // Your cell height here...
override func prepare() {
super.prepare()
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
var layoutAttrs = [UICollectionViewLayoutAttributes]()
if let collectionView = self.collectionView {
for section in 0 ..< collectionView.numberOfSections {
if let numberOfSectionItems = numberOfItemsInSection(section) {
for item in 0 ..< numberOfSectionItems {
let indexPath = IndexPath(item: item, section: section)
let layoutAttr = layoutAttributesForItem(at: indexPath)
if let layoutAttr = layoutAttr, layoutAttr.frame.intersects(rect) {
layoutAttrs.append(layoutAttr)
}
}
}
}
}
return layoutAttrs
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
let layoutAttr = UICollectionViewLayoutAttributes(forCellWith: indexPath)
let contentSize = self.collectionViewContentSize
layoutAttr.frame = CGRect(
x: 0, y: contentSize.height - CGFloat(indexPath.item + 1) * cellHeight,
width: contentSize.width, height: cellHeight)
return layoutAttr
}
func numberOfItemsInSection(_ section: Int) -> Int? {
if let collectionView = self.collectionView,
let numSectionItems = collectionView.dataSource?.collectionView(collectionView, numberOfItemsInSection: section)
{
return numSectionItems
}
return 0
}
override var collectionViewContentSize: CGSize {
get {
var height: CGFloat = 0
var bounds: CGRect = .zero
if let collectionView = self.collectionView {
for section in 0 ..< collectionView.numberOfSections {
if let numItems = numberOfItemsInSection(section) {
height += CGFloat(numItems) * cellHeight
}
}
bounds = collectionView.bounds
}
return CGSize(width: bounds.width, height: max(height, bounds.height))
}
}
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
if let oldBounds = self.collectionView?.bounds,
oldBounds.width != newBounds.width || oldBounds.height != newBounds.height
{
return true
}
return false
}
}回答 3
Stack Overflow用户
回答已采纳
发布于 2018-10-06 12:31:51
用一个collectionView翻转你的CGAffineTransform，使它从底部开始。
collectionView.transform = CGAffineTransform(scaleX: 1, y: -1)现在唯一的问题是你所有的细胞都是颠倒显示的。然后将转换应用到每个单元格上，将其垂直翻转回来。
class InvertedCollectionViewFlowLayout: UICollectionViewFlowLayout {
// inverting the transform in the layout, rather than directly on the cell,
// is the only way I've found to prevent cells from flipping during animated
// cell updates
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
let attrs = super.layoutAttributesForItem(at: indexPath)
attrs?.transform = CGAffineTransform(scaleX: 1, y: -1)
return attrs
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
let attrsList = super.layoutAttributesForElements(in: rect)
if let list = attrsList {
for i in 0..<list.count {
list[i].transform = CGAffineTransform(scaleX: 1, y: -1)
}
}
return attrsList
}
}Stack Overflow用户
发布于 2019-03-16 07:42:17
UICollectionView具有反向流量布局和动态单元格和标头高度。
import Foundation
import UIKit
class InvertedFlowLayout: UICollectionViewFlowLayout {
override func prepare() {
super.prepare()
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard super.layoutAttributesForElements(in: rect) != nil else { return nil }
var attributesArrayNew = [UICollectionViewLayoutAttributes]()
if let collectionView = self.collectionView {
for section in 0 ..< collectionView.numberOfSections {
for item in 0 ..< collectionView.numberOfItems(inSection: section) {
let indexPathCurrent = IndexPath(item: item, section: section)
if let attributeCell = layoutAttributesForItem(at: indexPathCurrent) {
if attributeCell.frame.intersects(rect) {
attributesArrayNew.append(attributeCell)
}
}
}
}
for section in 0 ..< collectionView.numberOfSections {
let indexPathCurrent = IndexPath(item: 0, section: section)
if let attributeKind = layoutAttributesForSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, at: indexPathCurrent) {
attributesArrayNew.append(attributeKind)
}
}
}
return attributesArrayNew
}
override func layoutAttributesForSupplementaryView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
let attributeKind = UICollectionViewLayoutAttributes(forSupplementaryViewOfKind: elementKind, with: indexPath)
if let collectionView = self.collectionView {
var fullHeight: CGFloat = 0.0
for section in 0 ..< indexPath.section + 1 {
for item in 0 ..< collectionView.numberOfItems(inSection: section) {
let indexPathCurrent = IndexPath(item: item, section: section)
fullHeight += cellHeight(indexPathCurrent) + minimumLineSpacing
}
}
attributeKind.frame = CGRect(x: 0, y: collectionViewContentSize.height - fullHeight - CGFloat(indexPath.section + 1) * headerHeight(indexPath.section) - sectionInset.bottom + minimumLineSpacing/2, width: collectionViewContentSize.width, height: headerHeight(indexPath.section))
}
return attributeKind
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
let attributeCell = UICollectionViewLayoutAttributes(forCellWith: indexPath)
if let collectionView = self.collectionView {
var fullHeight: CGFloat = 0.0
for section in 0 ..< indexPath.section + 1 {
for item in 0 ..< collectionView.numberOfItems(inSection: section) {
let indexPathCurrent = IndexPath(item: item, section: section)
fullHeight += cellHeight(indexPathCurrent) + minimumLineSpacing
if section == indexPath.section && item == indexPath.item {
break
}
}
}
attributeCell.frame = CGRect(x: 0, y: collectionViewContentSize.height - fullHeight + minimumLineSpacing - CGFloat(indexPath.section) * headerHeight(indexPath.section) - sectionInset.bottom, width: collectionViewContentSize.width, height: cellHeight(indexPath) )
}
return attributeCell
}
override var collectionViewContentSize: CGSize {
get {
var height: CGFloat = 0.0
var bounds = CGRect.zero
if let collectionView = self.collectionView {
for section in 0 ..< collectionView.numberOfSections {
for item in 0 ..< collectionView.numberOfItems(inSection: section) {
let indexPathCurrent = IndexPath(item: item, section: section)
height += cellHeight(indexPathCurrent) + minimumLineSpacing
}
}
height += sectionInset.bottom + CGFloat(collectionView.numberOfSections) * headerHeight(0)
bounds = collectionView.bounds
}
return CGSize(width: bounds.width, height: max(height, bounds.height))
}
}
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
if let oldBounds = self.collectionView?.bounds,
oldBounds.width != newBounds.width || oldBounds.height != newBounds.height {
return true
}
return false
}
func cellHeight(_ indexPath: IndexPath) -> CGFloat {
if let collectionView = self.collectionView, let delegateFlowLayout = collectionView.delegate as? UICollectionViewDelegateFlowLayout {
let size = delegateFlowLayout.collectionView!(collectionView, layout: self, sizeForItemAt: indexPath)
return size.height
}
return 0
}
func headerHeight(_ section: Int) -> CGFloat {
if let collectionView = self.collectionView, let delegateFlowLayout = collectionView.delegate as? UICollectionViewDelegateFlowLayout {
let size = delegateFlowLayout.collectionView!(collectionView, layout: self, referenceSizeForHeaderInSection: section)
return size.height
}
return 0
}
}Stack Overflow用户
发布于 2017-11-30 06:51:16
您可以旋转(转换) collectionView 180度，因此顶部将在底部和旋转(转换)每个单元格180，使他们看起来正常。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/47562091
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