[英]How do you determine spacing between cells in UICollectionView flowLayout
我有一个带有流布局的 UICollectionView，每个单元格都是一个正方形。 如何确定每行每个单元格之间的间距？ 我似乎无法为此找到合适的设置。 我看到 nib 文件上有一个用于集合视图的最小间距属性，但我将其设置为 0 并且单元格甚至不粘连。
还有其他想法吗？
更新：此答案的 Swift 版本： https : //github.com/fanpyi/UICollectionViewLeftAlignedLayout-Swift
在@matt 的带领下，我修改了他的代码以确保项目始终左对齐。 我发现如果一个项目自己结束在一行上，它会以流布局为中心。 我进行了以下更改以解决此问题。
只有当单元格宽度不同时才会发生这种情况，这可能会导致如下布局。 由于UICollectionViewFlowLayout的行为，最后一行总是左对齐，问题在于除最后一行之外的任何一行中的项目。
使用@matt 的代码，我看到了。
在那个例子中，我们看到如果单元格自己最终在线上，它们就会居中。 下面的代码确保您的集合视图看起来像这样。
#import "CWDLeftAlignedCollectionViewFlowLayout.h"
const NSInteger kMaxCellSpacing = 9;
@implementation CWDLeftAlignedCollectionViewFlowLayout
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
NSArray* attributesToReturn = [super layoutAttributesForElementsInRect:rect];
for (UICollectionViewLayoutAttributes* attributes in attributesToReturn) {
if (nil == attributes.representedElementKind) {
NSIndexPath* indexPath = attributes.indexPath;
attributes.frame = [self layoutAttributesForItemAtIndexPath:indexPath].frame;
}
}
return attributesToReturn;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes* currentItemAttributes =
[super layoutAttributesForItemAtIndexPath:indexPath];
UIEdgeInsets sectionInset = [(UICollectionViewFlowLayout *)self.collectionView.collectionViewLayout sectionInset];
CGRect currentFrame = currentItemAttributes.frame;
if (indexPath.item == 0) { // first item of section
currentFrame.origin.x = sectionInset.left; // first item of the section should always be left aligned
currentItemAttributes.frame = currentFrame;
return currentItemAttributes;
}
NSIndexPath* previousIndexPath = [NSIndexPath indexPathForItem:indexPath.item-1 inSection:indexPath.section];
CGRect previousFrame = [self layoutAttributesForItemAtIndexPath:previousIndexPath].frame;
CGFloat previousFrameRightPoint = CGRectGetMaxX(previousFrame) + kMaxCellSpacing;
CGRect strecthedCurrentFrame = CGRectMake(0,
currentFrame.origin.y,
self.collectionView.frame.size.width,
currentFrame.size.height);
if (!CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)) { // if current item is the first item on the line
// the approach here is to take the current frame, left align it to the edge of the view
// then stretch it the width of the collection view, if it intersects with the previous frame then that means it
// is on the same line, otherwise it is on it's own new line
currentFrame.origin.x = sectionInset.left; // first item on the line should always be left aligned
currentItemAttributes.frame = currentFrame;
return currentItemAttributes;
}
currentFrame.origin.x = previousFrameRightPoint;
currentItemAttributes.frame = currentFrame;
return currentItemAttributes;
}
@end
要获得最大的项目间间距，子类 UICollectionViewFlowLayout 并覆盖layoutAttributesForElementsInRect:和layoutAttributesForItemAtIndexPath: 。
例如，一个常见的问题是：集合视图的行是左右对齐的，除了最后一行是左对齐的。 假设我们希望所有的线都左对齐，这样它们之间的空间就是 10 点。 这是一个简单的方法（在您的 UICollectionViewFlowLayout 子类中）：
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect {
NSArray* arr = [super layoutAttributesForElementsInRect:rect];
for (UICollectionViewLayoutAttributes* atts in arr) {
if (nil == atts.representedElementKind) {
NSIndexPath* ip = atts.indexPath;
atts.frame = [self layoutAttributesForItemAtIndexPath:ip].frame;
}
}
return arr;
}
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath {
UICollectionViewLayoutAttributes* atts =
[super layoutAttributesForItemAtIndexPath:indexPath];
if (indexPath.item == 0) // degenerate case 1, first item of section
return atts;
NSIndexPath* ipPrev =
[NSIndexPath indexPathForItem:indexPath.item-1 inSection:indexPath.section];
CGRect fPrev = [self layoutAttributesForItemAtIndexPath:ipPrev].frame;
CGFloat rightPrev = fPrev.origin.x + fPrev.size.width + 10;
if (atts.frame.origin.x <= rightPrev) // degenerate case 2, first item of line
return atts;
CGRect f = atts.frame;
f.origin.x = rightPrev;
atts.frame = f;
return atts;
}
这如此简单的原因是我们并没有真正执行布局的繁重工作； 我们正在利用 UICollectionViewFlowLayout 已经为我们完成的布局工作。 它已经决定了每行有多少项目； 如果你明白我的意思，我们只是在阅读这些行并将这些项目放在一起。
有几件事情需要考虑：
尝试更改 IB 中的最小间距，但将光标留在该字段中。 请注意，Xcode 不会立即将文档标记为已更改。 但是，当您单击不同的字段时，Xcode 会注意到文档已更改并在文件导航器中将其标记为更改。 因此，请务必在进行更改后使用 Tab 键或单击切换到不同的字段。
进行更改后保存您的故事板/xib 文件，并确保重建应用程序。 错过这一步并不难，然后你就会挠头想知道为什么你的更改似乎没有任何效果。
UICollectionViewFlowLayout有一个minimumInteritemSpacing属性，这是你在 IB 中设置的。 但是集合的委托也可以有一个方法来确定项目间的间距。 该方法胜过布局的属性，因此如果您在委托中实现它，则不会使用布局的属性。
请记住，间距有一个最小间距。 布局将使用该数字（无论它来自属性还是来自委托方法）作为最小的允许空间，但如果行上有剩余空间，它可能会使用更大的空间。 因此，例如，如果您将最小间距设置为 0，您可能仍会在项目之间看到几个像素。 如果您想更好地控制项目的确切间距，您可能应该使用不同的布局（可能是您自己创建的布局之一）。
一点数学知识可以更轻松地解决问题。 Chris Wagner 编写的代码很糟糕，因为它调用了之前每个项目的布局属性。 所以你滚动得越多，它就越慢......
只需像这样使用模（我也使用我的 minimumInteritemSpacing 值作为最大值）：
- (UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
UICollectionViewLayoutAttributes* currentItemAttributes = [super layoutAttributesForItemAtIndexPath:indexPath];
NSInteger numberOfItemsPerLine = floor([self collectionViewContentSize].width / [self itemSize].width);
if (indexPath.item % numberOfItemsPerLine != 0)
{
NSInteger cellIndexInLine = (indexPath.item % numberOfItemsPerLine);
CGRect itemFrame = [currentItemAttributes frame];
itemFrame.origin.x = ([self itemSize].width * cellIndexInLine) + ([self minimumInteritemSpacing] * cellIndexInLine);
currentItemAttributes.frame = itemFrame;
}
return currentItemAttributes;
}
左对齐的一种简单方法是在 UICollectionViewFlowLayout 的子类中修改 layoutAttributesForElementsInRect: ：
- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect
{
NSArray *allLayoutAttributes = [super layoutAttributesForElementsInRect:rect];
CGRect prevFrame = CGRectMake(-FLT_MAX, -FLT_MAX, 0, 0);
for (UICollectionViewLayoutAttributes *layoutAttributes in allLayoutAttributes)
{
//fix blur
CGRect theFrame = CGRectIntegral(layoutAttributes.frame);
//left justify
if(prevFrame.origin.x > -FLT_MAX &&
prevFrame.origin.y >= theFrame.origin.y &&
prevFrame.origin.y <= theFrame.origin.y) //workaround for float == warning
{
theFrame.origin.x = prevFrame.origin.x +
prevFrame.size.width +
EXACT_SPACE_BETWEEN_ITEMS;
}
prevFrame = theFrame;
layoutAttributes.frame = theFrame;
}
return allLayoutAttributes;
}
Clean Swift 解决方案，来自进化史：
open class UICollectionViewLeftAlignedLayout: UICollectionViewFlowLayout {
open override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
return super.layoutAttributesForElements(in: rect)?.map { $0.representedElementKind == nil ? layoutAttributesForItem(at: $0.indexPath)! : $0 }
}
open override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
guard let currentItemAttributes = super.layoutAttributesForItem(at: indexPath)?.copy() as? UICollectionViewLayoutAttributes,
collectionView != nil else {
// should never happen
return nil
}
// if the current frame, once stretched to the full row intersects the previous frame then they are on the same row
if indexPath.item != 0,
let previousFrame = layoutAttributesForItem(at: IndexPath(item: indexPath.item - 1, section: indexPath.section))?.frame,
currentItemAttributes.frame.intersects(CGRect(x: -.infinity, y: previousFrame.origin.y, width: .infinity, height: previousFrame.size.height)) {
// the next item on a line
currentItemAttributes.frame.origin.x = previousFrame.origin.x + previousFrame.size.width + evaluatedMinimumInteritemSpacingForSection(at: indexPath.section)
} else {
// the first item on a line
currentItemAttributes.frame.origin.x = evaluatedSectionInsetForSection(at: indexPath.section).left
}
return currentItemAttributes
}
func evaluatedMinimumInteritemSpacingForSection(at section: NSInteger) -> CGFloat {
return (collectionView?.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView?(collectionView!, layout: self, minimumInteritemSpacingForSectionAt: section) ?? minimumInteritemSpacing
}
func evaluatedSectionInsetForSection(at index: NSInteger) -> UIEdgeInsets {
return (collectionView?.delegate as? UICollectionViewDelegateFlowLayout)?.collectionView?(collectionView!, layout: self, insetForSectionAt: index) ?? sectionInset
}
}
用法：项目之间的间距由委托的collectionView (_:layout:minimumInteritemSpacingForSectionAt:) 。
我把它放在 github 上， https://github.com/Coeur/UICollectionViewLeftAlignedLayout ，我实际上在那里添加了一个支持两个滚动方向（水平和垂直）的功能。
Chris 解决方案的快速版本。
class PazLeftAlignedCollectionViewFlowLayout : UICollectionViewFlowLayout {
var maxCellSpacing = 14.0
override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
if var attributesToReturn = super.layoutAttributesForElementsInRect(rect) as? Array<UICollectionViewLayoutAttributes> {
for attributes in attributesToReturn {
if attributes.representedElementKind == nil {
let indexPath = attributes.indexPath
attributes.frame = self.layoutAttributesForItemAtIndexPath(indexPath).frame;
}
}
return attributesToReturn;
}
return super.layoutAttributesForElementsInRect(rect)
}
override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes! {
let currentItemAttributes = super.layoutAttributesForItemAtIndexPath(indexPath)
if let collectionViewFlowLayout = self.collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
let sectionInset = collectionViewFlowLayout.sectionInset
if (indexPath.item == 0) { // first item of section
var frame = currentItemAttributes.frame;
frame.origin.x = sectionInset.left; // first item of the section should always be left aligned
currentItemAttributes.frame = frame;
return currentItemAttributes;
}
let previousIndexPath = NSIndexPath(forItem:indexPath.item-1, inSection:indexPath.section)
let previousFrame = self.layoutAttributesForItemAtIndexPath(previousIndexPath).frame;
let previousFrameRightPoint = Double(previousFrame.origin.x) + Double(previousFrame.size.width) + self.maxCellSpacing
let currentFrame = currentItemAttributes.frame
var width : CGFloat = 0.0
if let collectionViewWidth = self.collectionView?.frame.size.width {
width = collectionViewWidth
}
let strecthedCurrentFrame = CGRectMake(0,
currentFrame.origin.y,
width,
currentFrame.size.height);
if (!CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)) { // if current item is the first item on the line
// the approach here is to take the current frame, left align it to the edge of the view
// then stretch it the width of the collection view, if it intersects with the previous frame then that means it
// is on the same line, otherwise it is on it's own new line
var frame = currentItemAttributes.frame;
frame.origin.x = sectionInset.left; // first item on the line should always be left aligned
currentItemAttributes.frame = frame;
return currentItemAttributes;
}
var frame = currentItemAttributes.frame;
frame.origin.x = CGFloat(previousFrameRightPoint)
currentItemAttributes.frame = frame;
}
return currentItemAttributes;
}
}
要使用它，请执行以下操作：
override func viewDidLoad() {
super.viewDidLoad()
self.collectionView.collectionViewLayout = self.layout
}
var layout : PazLeftAlignedCollectionViewFlowLayout {
var layout = PazLeftAlignedCollectionViewFlowLayout()
layout.itemSize = CGSizeMake(220.0, 230.0)
layout.minimumLineSpacing = 12.0
return layout
}
UICollectionViewFlowLayout的“问题”在于它对单元格应用了对齐方式：一行中的第一个单元格左对齐，一行中的最后一个单元格右对齐，中间的所有其他单元格均匀分布间距大于minimumInteritemSpacing 。
这篇文章已经有很多很好的答案，它们通过UICollectionViewFlowLayout来解决这个问题。 因此，您会得到一个将单元格向左对齐的布局。 以恒定间距分布单元格的另一个有效解决方案是将单元格右对齐。
我还创建了一个UICollectionViewFlowLayout子类，它遵循matt和Chris Wagner建议的类似想法，可以对齐单元格
⬅︎左：
或➡︎右:
您可以简单地从这里下载它，将布局文件添加到您的项目并将AlignedCollectionViewFlowLayout设置为您的集合视图的布局类：
https://github.com/mischa-hildebrand/AlignedCollectionViewFlowLayout
+---------+----------------------------------------------------------------+---------+
| | | |
| | +------------+ | |
| | | | | |
| section |- - -|- - - - - - |- - - - +---------------------+ - - - - - - -| section |
| inset | |intersection| | | line rect | inset |
| |- - -|- - - - - - |- - - - +---------------------+ - - - - - - -| |
| (left) | | | current item | (right) |
| | +------------+ | |
| | previous item | |
+---------+----------------------------------------------------------------+---------+
这里的概念是检查索引为i的当前单元格和索引为i−1的前一个单元格是否占据同一行。
...你做同样的反之亦然，即你检查下一个带有索引i+1 的单元格。
您可以通过两种方式做到这一点。
首先，在layoutAttributesForItem做一些修改，
通过之前的layoutAttributesForItem(at: IndexPath(item: indexPath.item - 1, section: indexPath.section))?.frame获取当前属性的布局。
layoutAttributesForItem(at:)：此方法向集合视图提供按需布局信息。 您需要覆盖它并在请求的 indexPath 处返回项目的布局属性。
其次，通过UICollectionViewLayoutAttributes(forCellWith: indexPath)新建一些属性，将它们布置在你想要的任何地方。
数学有点大，因为它执行了布局的繁重工作。
layoutAttributesForElements(in:)：在此方法中，您需要返回给定矩形内所有项目的布局属性。 您将属性作为 UICollectionViewLayoutAttributes 数组返回到集合视图。
你可以检查 我的回购
基于 Chris Wagner 的回答，为感兴趣的人提供了一个更简洁的 swift 版本：
class AlignLeftFlowLayout: UICollectionViewFlowLayout {
var maximumCellSpacing = CGFloat(9.0)
override func layoutAttributesForElementsInRect(rect: CGRect) -> [AnyObject]? {
let attributesToReturn = super.layoutAttributesForElementsInRect(rect) as? [UICollectionViewLayoutAttributes]
for attributes in attributesToReturn ?? [] {
if attributes.representedElementKind == nil {
attributes.frame = self.layoutAttributesForItemAtIndexPath(attributes.indexPath).frame
}
}
return attributesToReturn
}
override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes! {
let curAttributes = super.layoutAttributesForItemAtIndexPath(indexPath)
let sectionInset = (self.collectionView?.collectionViewLayout as UICollectionViewFlowLayout).sectionInset
if indexPath.item == 0 {
let f = curAttributes.frame
curAttributes.frame = CGRectMake(sectionInset.left, f.origin.y, f.size.width, f.size.height)
return curAttributes
}
let prevIndexPath = NSIndexPath(forItem: indexPath.item-1, inSection: indexPath.section)
let prevFrame = self.layoutAttributesForItemAtIndexPath(prevIndexPath).frame
let prevFrameRightPoint = prevFrame.origin.x + prevFrame.size.width + maximumCellSpacing
let curFrame = curAttributes.frame
let stretchedCurFrame = CGRectMake(0, curFrame.origin.y, self.collectionView!.frame.size.width, curFrame.size.height)
if CGRectIntersectsRect(prevFrame, stretchedCurFrame) {
curAttributes.frame = CGRectMake(prevFrameRightPoint, curFrame.origin.y, curFrame.size.width, curFrame.size.height)
} else {
curAttributes.frame = CGRectMake(sectionInset.left, curFrame.origin.y, curFrame.size.width, curFrame.size.height)
}
return curAttributes
}
}
这里是 NSCollectionViewFlowLayout
class LeftAlignedCollectionViewFlowLayout: NSCollectionViewFlowLayout {
var maximumCellSpacing = CGFloat(2.0)
override func layoutAttributesForElementsInRect(rect: NSRect) -> [NSCollectionViewLayoutAttributes] {
let attributesToReturn = super.layoutAttributesForElementsInRect(rect)
for attributes in attributesToReturn ?? [] {
if attributes.representedElementKind == nil {
attributes.frame = self.layoutAttributesForItemAtIndexPath(attributes.indexPath!)!.frame
}
}
return attributesToReturn
}
override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> NSCollectionViewLayoutAttributes? {
let curAttributes = super.layoutAttributesForItemAtIndexPath(indexPath)
let sectionInset = (self.collectionView?.collectionViewLayout as! NSCollectionViewFlowLayout).sectionInset
if indexPath.item == 0 {
let f = curAttributes!.frame
curAttributes!.frame = CGRectMake(sectionInset.left, f.origin.y, f.size.width, f.size.height)
return curAttributes
}
let prevIndexPath = NSIndexPath(forItem: indexPath.item-1, inSection: indexPath.section)
let prevFrame = self.layoutAttributesForItemAtIndexPath(prevIndexPath)!.frame
let prevFrameRightPoint = prevFrame.origin.x + prevFrame.size.width + maximumCellSpacing
let curFrame = curAttributes!.frame
let stretchedCurFrame = CGRectMake(0, curFrame.origin.y, self.collectionView!.frame.size.width, curFrame.size.height)
if CGRectIntersectsRect(prevFrame, stretchedCurFrame) {
curAttributes!.frame = CGRectMake(prevFrameRightPoint, curFrame.origin.y, curFrame.size.width, curFrame.size.height)
} else {
curAttributes!.frame = CGRectMake(sectionInset.left, curFrame.origin.y, curFrame.size.width, curFrame.size.height)
}
return curAttributes
}
}
基于 mokagio 的 swift 版本： https : //github.com/fanpyi/UICollectionViewLeftAlignedLayout-Swift
class UICollectionViewLeftAlignedLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElementsInRect(rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
let attributesToReturn = super.layoutAttributesForElementsInRect(rect)
if let attributesToReturn = attributesToReturn {
for attributes in attributesToReturn {
if attributes.representedElementKind == nil {
let indexpath = attributes.indexPath
if let attr = layoutAttributesForItemAtIndexPath(indexpath) {
attributes.frame = attr.frame
}
}
}
}
return attributesToReturn
}
override func layoutAttributesForItemAtIndexPath(indexPath: NSIndexPath) -> UICollectionViewLayoutAttributes? {
if let currentItemAttributes = super.layoutAttributesForItemAtIndexPath(indexPath){
let sectionInset = self.evaluatedSectionInsetForItemAtIndex(indexPath.section)
let isFirstItemInSection = indexPath.item == 0;
let layoutWidth = CGRectGetWidth(self.collectionView!.frame) - sectionInset.left - sectionInset.right;
if (isFirstItemInSection) {
currentItemAttributes.leftAlignFrameWithSectionInset(sectionInset)
return currentItemAttributes
}
let previousIndexPath = NSIndexPath(forItem: indexPath.item - 1, inSection: indexPath.section)
let previousFrame = layoutAttributesForItemAtIndexPath(previousIndexPath)?.frame ?? CGRectZero
let previousFrameRightPoint = previousFrame.origin.x + previousFrame.width
let currentFrame = currentItemAttributes.frame;
let strecthedCurrentFrame = CGRectMake(sectionInset.left,
currentFrame.origin.y,
layoutWidth,
currentFrame.size.height)
// if the current frame, once left aligned to the left and stretched to the full collection view
// widht intersects the previous frame then they are on the same line
let isFirstItemInRow = !CGRectIntersectsRect(previousFrame, strecthedCurrentFrame)
if (isFirstItemInRow) {
// make sure the first item on a line is left aligned
currentItemAttributes.leftAlignFrameWithSectionInset(sectionInset)
return currentItemAttributes
}
var frame = currentItemAttributes.frame;
frame.origin.x = previousFrameRightPoint + evaluatedMinimumInteritemSpacingForSectionAtIndex(indexPath.section)
currentItemAttributes.frame = frame;
return currentItemAttributes;
}
return nil
}
func evaluatedMinimumInteritemSpacingForSectionAtIndex(sectionIndex:Int) -> CGFloat {
if let delegate = self.collectionView?.delegate as? UICollectionViewDelegateFlowLayout {
if delegate.respondsToSelector("collectionView:layout:minimumInteritemSpacingForSectionAtIndex:") {
return delegate.collectionView!(self.collectionView!, layout: self, minimumInteritemSpacingForSectionAtIndex: sectionIndex)
}
}
return self.minimumInteritemSpacing
}
func evaluatedSectionInsetForItemAtIndex(index: Int) ->UIEdgeInsets {
if let delegate = self.collectionView?.delegate as? UICollectionViewDelegateFlowLayout {
if delegate.respondsToSelector("collectionView:layout:insetForSectionAtIndex:") {
return delegate.collectionView!(self.collectionView!, layout: self, insetForSectionAtIndex: index)
}
}
return self.sectionInset
}
}
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