I have a tableview that has tableview cells that are populated with users posts on the app. users are able to have posts with just text or they can include an image with their text.
The problem i have is with setting the cell height depending on if the post contains an image. for example if the post contains an image i want the cell height = 400 but if it contains only text then i want the cell height = 150.
At the moment i have the height fixed at 400 using this code but i don't know how to make the above modifications.
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
//auto cell height
return 400
}
post model looks like this...
class Posts {
var id: String
var author: String
var text: String
var createdAt: Date
var degree: String
var university: String
var uid: String
var photoURL: String
var url: URL
var postID: String
var likes: Int
init(id:String, author:String, text:String, timestamp:Double, degree:String, university:String, uid:String, photoURL:String, url:URL, postID:String, likes:Int) {
self.id = id
self.author = author
self.text = text
self.createdAt = Date(timeIntervalSince1970: timestamp / 1000)
self.degree = degree
self.university = university
self.uid = uid
self.photoURL = photoURL
self.url = url
self.postID = postID
self.likes = likes
}
}
One decently easy way to do this is to create a custom view cell and hide the imageView if needed.
Create the custom tableView cell and make sure to add a .xib file to be able to edit everything visually:
Set the row height to automatic so that the tableView knows to set the height to whatever you need.
Then, you can add your text and imageView onto this custom cell. The way I've gotten this to work before is to add both elements into a stackView and set up constraints on that.
Make sure you have constraints set up for the height the label and imageView inside of the stackView and the distance from the stackView to the bottom and top of the superView. This lets auto layout know how tall to make the cell
Now, any time you hide the imageView (when you don't have an image to display) the cell should autoresize to be smaller.
I ended up adding this code to the tableview cellforrowat index path function in order to get the images rendering correctly.
let imageIndex = posts[indexPath.row].mediaURL
let url = NSURL(string: imageIndex)! as URL
if let imageData: NSData = NSData(contentsOf: url) {
let image = UIImage(data: imageData as Data)
let newWidth = cell.MediaPhoto.frame.width
let scale = newWidth/image!.size.width
let newHeight = image!.size.height * scale
UIGraphicsBeginImageContext(CGSize(width: newWidth, height: newHeight))
image!.draw(in: CGRect(x: 0, y: 0, width: newWidth, height: newHeight))
let newImage = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()
cell.MediaPhoto.image = newImage
cell.MediaPhoto.contentMode = .scaleToFill
cell.MediaPhoto.clipsToBounds = true
I have the following UICollectionView:
It has vertical scrolling, 1 section and 31 items.
It has the basic setup and I am calculating itemSize to fit exactly 7 per row.
Currently it looks like this:
However, I would like to make an inset before first item, so that the layout is even and there are the same number of items in first and last row. This is static and will always contain 31 items, so I am basically trying to add left space/inset before first item, so that it looks like this:
I have tried using a custom UICollectionViewDelegateFlowLayout method:
collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int)
But since there is only 1 section with 31 rows, it insets all of the rows, not just the first.
I know I could probably add two more "blank" items, but I feel like there is a better solution I may not be aware of. Any ideas?
EDIT: I've tried Tarun's answer, but this doesn't work. Origin of first item changes, but the rest stays as is, therefore first overlaps the second and the rest remain as they were. Shifting them all doesn't work either. I ended up with:
You need to subclass UICollectionViewFlowLayout and that will provide you a chance to customize the frame for all items within the collectionView.
import UIKit
class LeftAlignCellCollectionFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard let attributes = super.layoutAttributesForElements(in: rect) else { return nil }
guard let collectionView = self.collectionView else { return nil }
var newAttributes: [UICollectionViewLayoutAttributes] = []
let leftMargin = self.sectionInset.left
let layout = collectionView.collectionViewLayout
for attribute in attributes {
if let cellAttribute = layout.layoutAttributesForItem(at: attribute.indexPath) {
// Check for `indexPath.item == 0` & do what you want
// cellAttribute.frame.origin.x = 0 // 80
newAttributes.append(cellAttribute)
}
}
return newAttributes
}
}
Now you can use this custom layout class as your flow layout like following.
let flowLayout = LeftAlignCellCollectionFlowLayout()
collectionView.collectionViewLayout = flowLayout
Following Taran's suggestion, I've decided to use a custom UICollectionViewFlowLayout. Here is a generic answer that works for any number of items in the collectionView, as well as any inset value:
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard let collectionView = self.collectionView else { return nil }
guard let attributes = super.layoutAttributesForElements(in: rect) else { return nil }
var newAttributes: [UICollectionViewLayoutAttributes] = []
for attribute in attributes {
if let cellAttribute = collectionView.collectionViewLayout.layoutAttributesForItem(at: attribute.indexPath) {
let itemSize = cellAttribute.frame.size.width + self.minimumInteritemSpacing
let targetOriginX = cellAttribute.frame.origin.x + CGFloat(self.itemInset) * itemSize
if targetOriginX <= collectionView.bounds.size.width {
cellAttribute.frame.origin.x = targetOriginX
} else {
let shiftedPosition = lround(Double((targetOriginX / itemSize).truncatingRemainder(dividingBy: CGFloat(self.numberOfColumns))))
cellAttribute.frame.origin.x = itemSize * CGFloat(shiftedPosition)
cellAttribute.frame.origin.y += itemSize
}
newAttributes.append(cellAttribute)
}
}
return newAttributes
}
where:
self.itemInset is the value we want to inset from the left (2 for my initial question, but it can be any number from 0 to the number of columns-1)
self.numberOfColumns is - as the name suggests - number of columns in the collectionView. This pertains to the number of days in my example and would always be equal to 7, but one might want this to be a generic value for some other use case.
Just for the sake of the completeness, I provide a method that calculates a size for my callendar collection view, based on the number of columns (days):
private func collectionViewItemSize() -> CGSize {
let dimension = self.collectionView.frame.size.width / CGFloat(Constants.numberOfDaysInWeek) - Constants.minimumInteritemSpacing
return CGSize(width: dimension, height: dimension)
}
For me, Constants.numberOfDaysInWeek is naturally 7, and Constants.minimumInteritemSpacing is equal to 2, but those can be any numbers you desire.
I have vertical collection-view inside tableview cell. collection view contain feature of load more too. for self sizing of collection view, i make tableview cell automaticDimension.
Also i have give height constant to collection-view. first time its loaded correctly but once i go to last cell and its load-more after reloading it create lot of space after collection view. can any one let me know what i am doing wrong here. or is there any other way around to make collection-view inside tableview self sizing so it increase tableview cell height too
**
TableviewCell Class
**
justForYouCollectionView.dataSource = self
justForYouCollectionView.delegate = self
justForYouCollectionView.isScrollEnabled = false
self.collectionHeight.constant = self.justForYouCollectionView.collectionViewLayout.collectionViewContentSize.height
justForYouCollectionView.reloadData()
override func systemLayoutSizeFitting(_ targetSize: CGSize, withHorizontalFittingPriority horizontalFittingPriority: UILayoutPriority, verticalFittingPriority: UILayoutPriority) -> CGSize {
self.layoutIfNeeded()
let contentSize = self.justForYouCollectionView.collectionViewLayout.collectionViewContentSize
return CGSize(width: contentSize.width, height: contentSize.height + 20)
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if indexPath.row == self.justForYouArray.count - 1 && self.isLoadMore {
updateNextSet()
}
}
**
CollectionViewCell Class
**
override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
let autoLayoutAttributes = super.preferredLayoutAttributesFitting(layoutAttributes)
// Specify you want _full width_
let targetSize = CGSize(width: layoutAttributes.frame.width, height: 0)
// Calculate the size (height) using Auto Layout
let autoLayoutSize = contentView.systemLayoutSizeFitting(targetSize, withHorizontalFittingPriority: UILayoutPriority.required, verticalFittingPriority: UILayoutPriority.defaultLow)
let autoLayoutFrame = CGRect(origin: autoLayoutAttributes.frame.origin, size: autoLayoutSize)
// Assign the new size to the layout attributes
autoLayoutAttributes.frame = autoLayoutFrame
return autoLayoutAttributes
}
extra space can be seen in image
I have worked on that earlier all I did is, set tableview height constraint set in storyboard and drop its outlet in viewController then after populate data get array count and divide by 2 and after dividing I multiply it by CollectionViewCell height and set that height to the UITableView height constraint like this.
let count = (array.count / 2) * cellHeight
tableviewHeightConstraint.constant = CGFloat(count)
This will solve your problem.
try
let a = (yourArray.count /2 ) * heightCell
tblViewHeightConstraint.constant = CGFloat(a)
I have a UICollectionView with a flow layout and each cell is a square. How do I determine the spacing between each cells on each row? I can't seem to find the appropriate settings for this. I see there's a min spacing attributes on the nib file for a collection view, but I set this to 0 and the cells doesn't even stick.
Any other idea?
Update: Swift version of this answer: https://github.com/fanpyi/UICollectionViewLeftAlignedLayout-Swift
Taking #matt's lead I modified his code to insure that items are ALWAYS left aligned. I found that if an item ended up on a line by itself, it would be centered by the flow layout. I made the following changes to address this issue.
This situation would only ever occur if you have cells that vary in width, which could result in a layout like the following. The last line always left aligns due to the behavior of UICollectionViewFlowLayout, the issue lies in items that are by themselves in any line but the last one.
With #matt's code I was seeing.
In that example we see that cells get centered if they end up on the line by themselves. The code below insures your collection view would look like this.
#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
To get a maximum interitem spacing, subclass UICollectionViewFlowLayout and override layoutAttributesForElementsInRect: and layoutAttributesForItemAtIndexPath:.
For example, a common problem is this: the rows of a collection view are right-and-left justified, except for the last line which is left-justified. Let's say we want all the lines to be left-justified, so that the space between them is, let's say, 10 points. Here's an easy way (in your UICollectionViewFlowLayout subclass):
- (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;
}
The reason this is so easy is that we aren't really performing the heavy lifting of the layout; we are leveraging the layout work that UICollectionViewFlowLayout has already done for us. It has already decided how many items go in each line; we're just reading those lines and shoving the items together, if you see what I mean.
There are a few things to consider:
Try changing the minimum spacing in IB, but leave the cursor in that field. Notice that Xcode doesn't immediately mark the document as changed. When you click in a different field, though, Xcode does notice that the document is changed and marks it so in the file navigator. So, be sure to tab or click over to a different field after making a change.
Save your storyboard/xib file after making a change, and be sure to rebuild the app. It's not hard to miss that step, and then you're left scratching your head wondering why your changes didn't seem to have any effect.
UICollectionViewFlowLayout has a minimumInteritemSpacing property, which is what you're setting in IB. But the collection's delegate can also have a method to determine the inter-item spacing. That method trump's the layout's property, so if you implement it in your delegate your layout's property won't be used.
Remember that the spacing there is a minimum spacing. The layout will use that number (whether it comes from the property or from the delegate method) as the smallest allowable space, but it may use a larger space if it has space leftover on the line. So if, for example, you set the minimum spacing to 0, you may still see a few pixels between items. If you want more control over exactly how the items are spaced you should probably use a different layout (possibly one of your own creation).
A little bit of maths does the trick more easily. The code wrote by Chris Wagner is horrible because it calls the layout attributes of each previous items. So the more you scroll, the more it's slow...
Just use modulo like this (I'm using my minimumInteritemSpacing value as a max value too):
- (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;
}
An easy way to left-justify is to modify layoutAttributesForElementsInRect: in your subclass of UICollectionViewFlowLayout:
- (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 solution, from an history of evolution:
there was matt answer
there was Chris Wagner lone items fix
there was mokagio sectionInset and minimumInteritemSpacing improvement
there was fanpyi Swift version
now here is a simplified and clean version of mine:
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
}
}
Usage: the spacing between items is determined by delegate's collectionView (_:layout:minimumInteritemSpacingForSectionAt:).
I put it on github, https://github.com/Coeur/UICollectionViewLeftAlignedLayout, where I actually added a feature of supporting both scroll directions (horizontal and vertical).
The swift version of Chris solution.
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;
}
}
To use it do the following:
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
}
The "problem" with UICollectionViewFlowLayout is that it applies a justified align to the cells: The first cell in a row is left-aligned, the last cell in a row is right-aligned and all other cells in between are evenly distributed with an equal spacing that's greater than the minimumInteritemSpacing.
There are already many great answers to this post that solve this problem by subclassing UICollectionViewFlowLayout. As a result you get a layout that aligns the cells left. Another valid solution to distribute the cells with a constant spacing is to align the cells right.
AlignedCollectionViewFlowLayout
I've created a UICollectionViewFlowLayout subclass as well that follows a similar idea as suggested by matt and Chris Wagner that can either align the cells
⬅︎ left:
or ➡︎ right:
You can simply download it from here, add the layout file to your project and set AlignedCollectionViewFlowLayout as your collection view's layout class:
https://github.com/mischa-hildebrand/AlignedCollectionViewFlowLayout
How it works (for left-aligned cells):
+---------+----------------------------------------------------------------+---------+
| | | |
| | +------------+ | |
| | | | | |
| section |- - -|- - - - - - |- - - - +---------------------+ - - - - - - -| section |
| inset | |intersection| | | line rect | inset |
| |- - -|- - - - - - |- - - - +---------------------+ - - - - - - -| |
| (left) | | | current item | (right) |
| | +------------+ | |
| | previous item | |
+---------+----------------------------------------------------------------+---------+
The concept here is to check if the current cell with index i and the previous cell with the index i−1 occupy the same line.
If they don't the cell with index i is the left most cell in the line.
→ Move the cell to the left edge of the collection view (without changing its vertical position).
If they do, the cell with index i is not the left most cell in the line.
→ Get the previous cell's frame (with the index i−1) and move the current cell next to it.
For right-aligned cells...
... you do the same vice-versa, i.e. you check the next cell with the index i+1 instead.
You can do it in two ways.
Firstly, do some modification in layoutAttributesForItem,
get the current attributes's layout via the previous layoutAttributesForItem(at: IndexPath(item: indexPath.item - 1, section: indexPath.section))?.frame.
layoutAttributesForItem(at:): This method provides on demand layout information to the collection view. You need to override it and return the layout attributes for the item at the requested indexPath.
Secondly, new some attributes via UICollectionViewLayoutAttributes(forCellWith: indexPath),layout them wherever you want.
And the math is a little larger, because it performs the heavy lifting of the layout.
layoutAttributesForElements(in:): In this method you need to return the layout attributes for all the items inside the given rectangle. You return the attributes to the collection view as an array of UICollectionViewLayoutAttributes.
You can check My repo
you can put items left aligned
you can put items right aligned
you can put items right aligned and items reversed
A cleaner swift version for people interested, based on Chris Wagner's answer:
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
}
}
Here it is for 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
}
}
a swift version base on mokagio: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
}
}