UICollectionView 反向布局 [英] UICollectionView reverse Layout
本文介绍了UICollectionView 反向布局的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
我遇到了一个问题,我想让 CollectionView 像一个聊天".比我应该反转 UICollectionView
的布局.我可以配置 contentOffset = (0; 0) 将在底部 UICollectionView
的布局(并且 important 我不能 transform
CollectionView)?喜欢
I've got a problem, i want make CollectionView like a 'chat'. Than i should reverse Layout of UICollectionView
. Can i configure layout that contentOffset = (0; 0) will be on bottom UICollectionView
(and important i can't transform
CollectionView)?
Like
-> constenOffset = (0; 1000) (for example)
| ... |
| 2 |
| 1 |
| 0 |
-> constentOffset = (0; 0)
我也尝试旋转 UITableView
但在这种情况下 reloadSection
动画不满足我.
Also I tried to rotate UITableView
but in this case reloadSection
animation does not satisfy me.
推荐答案
具有反向流布局的 UICollectionView.
UICollectionView with a reversed flow layout.
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
}
}
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