UICollectionView - dynamic cell height?
Here is a Ray Wenderlich tutorial that shows you how to use AutoLayout to dynamically size UITableViewCell
s. I would think it would be the same for UICollectionViewCell
.
Basically, though, you end up dequeueing and configuring a prototype cell and grabbing its height. After reading this article, I decided to NOT implement this method and just write some clear, explicit sizing code.
Here's what I consider the "secret sauce" for the entire article:
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath {
return [self heightForBasicCellAtIndexPath:indexPath];
}
- (CGFloat)heightForBasicCellAtIndexPath:(NSIndexPath *)indexPath {
static RWBasicCell *sizingCell = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sizingCell = [self.tableView dequeueReusableCellWithIdentifier:RWBasicCellIdentifier];
});
[self configureBasicCell:sizingCell atIndexPath:indexPath];
return [self calculateHeightForConfiguredSizingCell:sizingCell];
}
- (CGFloat)calculateHeightForConfiguredSizingCell:(UITableViewCell *)sizingCell {
[sizingCell setNeedsLayout];
[sizingCell layoutIfNeeded];
CGSize size = [sizingCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
return size.height + 1.0f; // Add 1.0f for the cell separator height
}
EDIT: I did some research into your crash and decided that there is no way to get this done without a custom XIB. While that is a bit frustrating, you should be able to cut and paste from your Storyboard to a custom, empty XIB.
Once you've done that, code like the following will get you going:
// ViewController.m
#import "ViewController.h"
#import "CollectionViewCell.h"
@interface ViewController () <UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout> {
}
@property (weak, nonatomic) IBOutlet CollectionViewCell *cell;
@property (weak, nonatomic) IBOutlet UICollectionView *collectionView;
@end
@implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.view.backgroundColor = [UIColor lightGrayColor];
[self.collectionView registerNib:[UINib nibWithNibName:@"CollectionViewCell" bundle:nil] forCellWithReuseIdentifier:@"cell"];
}
- (void)viewDidAppear:(BOOL)animated {
[super viewDidAppear:animated];
NSLog(@"viewDidAppear...");
}
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return 1;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return 50;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
return 10.0f;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
return 10.0f;
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout *)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
return [self sizingForRowAtIndexPath:indexPath];
}
- (CGSize)sizingForRowAtIndexPath:(NSIndexPath *)indexPath {
static NSString *title = @"This is a long title that will cause some wrapping to occur. This is a long title that will cause some wrapping to occur.";
static NSString *subtitle = @"This is a long subtitle that will cause some wrapping to occur. This is a long subtitle that will cause some wrapping to occur.";
static NSString *buttonTitle = @"This is a really long button title that will cause some wrapping to occur.";
static CollectionViewCell *sizingCell = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sizingCell = [[NSBundle mainBundle] loadNibNamed:@"CollectionViewCell" owner:self options:nil][0];
});
[sizingCell configureWithTitle:title subtitle:[NSString stringWithFormat:@"%@: Number %d.", subtitle, (int)indexPath.row] buttonTitle:buttonTitle];
[sizingCell setNeedsLayout];
[sizingCell layoutIfNeeded];
CGSize cellSize = [sizingCell.contentView systemLayoutSizeFittingSize:UILayoutFittingCompressedSize];
NSLog(@"cellSize: %@", NSStringFromCGSize(cellSize));
return cellSize;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
static NSString *title = @"This is a long title that will cause some wrapping to occur. This is a long title that will cause some wrapping to occur.";
static NSString *subtitle = @"This is a long subtitle that will cause some wrapping to occur. This is a long subtitle that will cause some wrapping to occur.";
static NSString *buttonTitle = @"This is a really long button title that will cause some wrapping to occur.";
CollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
[cell configureWithTitle:title subtitle:[NSString stringWithFormat:@"%@: Number %d.", subtitle, (int)indexPath.row] buttonTitle:buttonTitle];
return cell;
}
@end
The code above (along with a very basic UICollectionViewCell
subclass and associated XIB) gives me this:
How to set Size for a specific cell when using dynamic size uicollectionView cell
Disclaimer: As OP had asked a question earlier on how to create a Pinterest layout and I had suggested Raywenderlich tutorial in comments, I believe this question from OP is extension of that
Answer:
Looking at the design you added, I believe you are trying to add a CollectionView
with a horizontal scroll as the first cell which spans the entire collection view width. Because you have subclassed the UICollectionViewFlowLayout
you need to handle this special case in prepare
method itself
override func prepare() {
// 1
guard
cache.isEmpty,
let collectionView = collectionView
else {
return
}
// 2
let columnWidth = contentWidth / CGFloat(numberOfColumns)
var xOffset: [CGFloat] = []
for column in 0..<numberOfColumns {
xOffset.append(CGFloat(column) * columnWidth)
}
var column = 0
var yOffset: [CGFloat] = .init(repeating: 0, count: numberOfColumns)
// 3
for item in 0..<collectionView.numberOfItems(inSection: 0) {
let indexPath = IndexPath(item: item, section: 0)
let attributes: UICollectionViewLayoutAttributes
let photoHeight = delegate?.collectionView(
collectionView,
heightForPhotoAtIndexPath: indexPath) ?? 180
let height = cellPadding * 2 + photoHeight
let frame: CGRect
if item == 0 {
frame = CGRect(x: 0,
y: yOffset[column],
width: columnWidth,
height: height)
contentHeight = frame.maxY
for column in 0..<numberOfColumns {
yOffset[column] = frame.maxY
}
column = 0
}
else {
// 4
frame = CGRect(x: xOffset[column],
y: yOffset[column],
width: columnWidth,
height: height)
contentHeight = max(contentHeight, frame.maxY)
yOffset[column] = yOffset[column] + height
column = column < (numberOfColumns - 1) ? (column + 1) : 0
}
let insetFrame = frame.insetBy(dx: cellPadding, dy: cellPadding)
attributes = UICollectionViewLayoutAttributes(forCellWith: indexPath)
attributes.frame = insetFrame
cache.append(attributes)
}
}
In your for item in 0..<collectionView.numberOfItems(inSection: 0) {
I have added a special condition for handling if item == 0 {
where in instead of using column width, I have used content width (as per your design you want first cell to cover the whole width of collection view)
Finally in your delegate method
extension PhotoStreamViewController: PinterestLayoutDelegate {
func collectionView(
_ collectionView: UICollectionView,
heightForPhotoAtIndexPath indexPath:IndexPath) -> CGFloat {
if indexPath.row == 0 {
return 180 // whatever is the height of first cell
}
return photos[indexPath.item].image.size.height
}
}
A word of caution
In your design I can see that you have added two section headers Header 1 and Header 2 I guess in that case your returning number of sections as at least 2, but the tutorial focuses on a single section collection view, if you notice
for item in 0..<collectionView.numberOfItems(inSection: 0) {
section 0 is hard coded, you might have to handle it dynamically if you wanna handle multiple sections and might need a lot of reworking around prepare
iOS - dynamically size width of a UICollectionViewCell
Try with This Way.
it's working fine for me in Swift5.
First Implement Collectionview FlowLayout Delegate
extension ItemViewController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
let text = "Your Lable Text"
let font: UIFont = UIFont(name: "Font Name", size: 20) ?? UIFont.systemFont(ofSize: 17.0) // set here font name and font size
let width = text.SizeOf(font).width
return CGSize(width: width + 20.0 , height: 40.0) // ADD width + space between text (for ex : 20.0)
}
}
Add One String Extension.
extension String {
func SizeOf(_ font: UIFont) -> CGSize {
return self.size(withAttributes: [NSAttributedString.Key.font: font])
}
}
UICollectionView, full width cells, allow autolayout dynamic height?
1. Solution for iOS 13+
With Swift 5.1 and iOS 13, you can use Compositional Layout objects in order to solve your problem.
The following complete sample code shows how to display multiline UILabel
inside full-width UICollectionViewCell
:
CollectionViewController.swift
import UIKit
class CollectionViewController: UICollectionViewController {
let items = [
[
"Lorem ipsum dolor sit amet.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris. Lorem ipsum dolor sit amet, consectetur adipiscing elit.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
],
[
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
],
[
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
"Lorem ipsum. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.",
]
]
override func viewDidLoad() {
super.viewDidLoad()
let size = NSCollectionLayoutSize(
widthDimension: NSCollectionLayoutDimension.fractionalWidth(1),
heightDimension: NSCollectionLayoutDimension.estimated(44)
)
let item = NSCollectionLayoutItem(layoutSize: size)
let group = NSCollectionLayoutGroup.horizontal(layoutSize: size, subitem: item, count: 1)
let section = NSCollectionLayoutSection(group: group)
section.contentInsets = NSDirectionalEdgeInsets(top: 10, leading: 10, bottom: 10, trailing: 10)
section.interGroupSpacing = 10
let headerFooterSize = NSCollectionLayoutSize(
widthDimension: .fractionalWidth(1.0),
heightDimension: .absolute(40)
)
let sectionHeader = NSCollectionLayoutBoundarySupplementaryItem(
layoutSize: headerFooterSize,
elementKind: "SectionHeaderElementKind",
alignment: .top
)
section.boundarySupplementaryItems = [sectionHeader]
let layout = UICollectionViewCompositionalLayout(section: section)
collectionView.collectionViewLayout = layout
collectionView.register(CustomCell.self, forCellWithReuseIdentifier: "CustomCell")
collectionView.register(HeaderView.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: "HeaderView")
}
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return items.count
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return items[section].count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell
cell.label.text = items[indexPath.section][indexPath.row]
return cell
}
override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: "HeaderView", for: indexPath) as! HeaderView
headerView.label.text = "Header"
return headerView
}
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
super.viewWillTransition(to: size, with: coordinator)
coordinator.animate(alongsideTransition: { context in
self.collectionView.collectionViewLayout.invalidateLayout()
}, completion: nil)
}
}
HeaderView.swift
import UIKit
class HeaderView: UICollectionReusableView {
let label = UILabel()
override init(frame: CGRect) {
super.init(frame: frame)
backgroundColor = .magenta
addSubview(label)
label.translatesAutoresizingMaskIntoConstraints = false
label.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true
label.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
CustomCell.swift
import UIKit
class CustomCell: UICollectionViewCell {
let label = UILabel()
override init(frame: CGRect) {
super.init(frame: frame)
label.numberOfLines = 0
backgroundColor = .orange
contentView.addSubview(label)
label.translatesAutoresizingMaskIntoConstraints = false
label.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
label.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
label.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
label.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
Expected display:
2. Solution for iOS 11+
With Swift 5.1 and iOS 11, you can subclass UICollectionViewFlowLayout
and set its estimatedItemSize
property to UICollectionViewFlowLayout.automaticSize
(this tells the system that you want to deal with autoresizing UICollectionViewCell
s). You'll then have to override layoutAttributesForElements(in:)
and layoutAttributesForItem(at:)
in order to set cells width. Lastly, you'll have to override your cell's preferredLayoutAttributesFitting(_:)
method and compute its height.
The following complete code shows how to display multiline UILabel
inside full-width UIcollectionViewCell
(constrained by UICollectionView
's safe area and UICollectionViewFlowLayout
's insets):
CollectionViewController.swift
import UIKit
class CollectionViewController: UICollectionViewController {
let items = [
[
"Lorem ipsum dolor sit amet.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris. Lorem ipsum dolor sit amet, consectetur adipiscing elit.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
],
[
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
],
[
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt.",
"Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
"Lorem ipsum. Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.",
]
]
let customFlowLayout = CustomFlowLayout()
override func viewDidLoad() {
super.viewDidLoad()
customFlowLayout.sectionInsetReference = .fromContentInset // .fromContentInset is default
customFlowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
customFlowLayout.minimumInteritemSpacing = 10
customFlowLayout.minimumLineSpacing = 10
customFlowLayout.sectionInset = UIEdgeInsets(top: 10, left: 10, bottom: 10, right: 10)
customFlowLayout.headerReferenceSize = CGSize(width: 0, height: 40)
collectionView.collectionViewLayout = customFlowLayout
collectionView.contentInsetAdjustmentBehavior = .always
collectionView.register(CustomCell.self, forCellWithReuseIdentifier: "CustomCell")
collectionView.register(HeaderView.self, forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: "HeaderView")
}
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return items.count
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return items[section].count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell
cell.label.text = items[indexPath.section][indexPath.row]
return cell
}
override func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: UICollectionView.elementKindSectionHeader, withReuseIdentifier: "HeaderView", for: indexPath) as! HeaderView
headerView.label.text = "Header"
return headerView
}
}
CustomFlowLayout.swift
import UIKit
final class CustomFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
let layoutAttributesObjects = super.layoutAttributesForElements(in: rect)?.map{ $0.copy() } as? [UICollectionViewLayoutAttributes]
layoutAttributesObjects?.forEach({ layoutAttributes in
if layoutAttributes.representedElementCategory == .cell {
if let newFrame = layoutAttributesForItem(at: layoutAttributes.indexPath)?.frame {
layoutAttributes.frame = newFrame
}
}
})
return layoutAttributesObjects
}
override func layoutAttributesForItem(at indexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
guard let collectionView = collectionView else {
fatalError()
}
guard let layoutAttributes = super.layoutAttributesForItem(at: indexPath)?.copy() as? UICollectionViewLayoutAttributes else {
return nil
}
layoutAttributes.frame.origin.x = sectionInset.left
layoutAttributes.frame.size.width = collectionView.safeAreaLayoutGuide.layoutFrame.width - sectionInset.left - sectionInset.right
return layoutAttributes
}
}
HeaderView.swift
import UIKit
class HeaderView: UICollectionReusableView {
let label = UILabel()
override init(frame: CGRect) {
super.init(frame: frame)
backgroundColor = .magenta
addSubview(label)
label.translatesAutoresizingMaskIntoConstraints = false
label.centerXAnchor.constraint(equalTo: centerXAnchor).isActive = true
label.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
CustomCell.swift
import UIKit
class CustomCell: UICollectionViewCell {
let label = UILabel()
override init(frame: CGRect) {
super.init(frame: frame)
label.numberOfLines = 0
backgroundColor = .orange
contentView.addSubview(label)
label.translatesAutoresizingMaskIntoConstraints = false
label.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
label.leadingAnchor.constraint(equalTo: contentView.leadingAnchor).isActive = true
label.trailingAnchor.constraint(equalTo: contentView.trailingAnchor).isActive = true
label.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
let layoutAttributes = super.preferredLayoutAttributesFitting(layoutAttributes)
layoutIfNeeded()
layoutAttributes.frame.size = systemLayoutSizeFitting(UIView.layoutFittingCompressedSize, withHorizontalFittingPriority: .required, verticalFittingPriority: .fittingSizeLevel)
return layoutAttributes
}
}
Here are some alternative implementations for preferredLayoutAttributesFitting(_:)
:
override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
let targetSize = CGSize(width: layoutAttributes.frame.width, height: 0)
layoutAttributes.frame.size = contentView.systemLayoutSizeFitting(targetSize, withHorizontalFittingPriority: .required, verticalFittingPriority: .fittingSizeLevel)
return layoutAttributes
}
override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
label.preferredMaxLayoutWidth = layoutAttributes.frame.width
layoutAttributes.frame.size.height = contentView.systemLayoutSizeFitting(UIView.layoutFittingCompressedSize).height
return layoutAttributes
}
Expected display:
Dynamic UICollectionView Cell Height
You could set the Estimated Size of the collectionView as "Automatic" as well as the cell's size and each cell will self size with Auto Layout constrained views.
As stated in the Xcode 11 Release Notes:
Cells in a UICollectionView can now self size with Auto Layout
constrained views in the canvas. To opt into the behavior for existing
collection views, enable “Automatic” for the collection view’s
estimated size, and “Automatic” for cell’s size from the Size
inspector. If deploying before iOS 13, you can activate self sizing
collection view cells by calling performBatchUpdates(_:completion:)
during viewDidLoad(). (45617083)
UICollectionView Self Sizing Cells with Auto Layout
This answer is outdated from iOS 14 with the addition of compositional layouts. Please consider updating the new API
Updated for Swift 5
preferredLayoutAttributesFittingAttributes
renamed to preferredLayoutAttributesFitting
and use auto sizing
Updated for Swift 4
systemLayoutSizeFittingSize
renamed to systemLayoutSizeFitting
Updated for iOS 9
After seeing my GitHub solution break under iOS 9 I finally got the time to investigate the issue fully. I have now updated the repo to include several examples of different configurations for self sizing cells. My conclusion is that self sizing cells are great in theory but messy in practice. A word of caution when proceeding with self sizing cells.
TL;DR
Check out my GitHub project
Self sizing cells are only supported with flow layout so make sure thats what you are using.
There are two things you need to setup for self sizing cells to work.
#1. Set estimatedItemSize
on UICollectionViewFlowLayout
Flow layout will become dynamic in nature once you set the estimatedItemSize
property.
self.flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
#2. Add support for sizing on your cell subclass
This comes in 2 flavours; Auto-Layout or custom override of preferredLayoutAttributesFittingAttributes
.
Create and configure cells with Auto Layout
I won't go to in to detail about this as there's a brilliant SO post about configuring constraints for a cell. Just be wary that Xcode 6 broke a bunch of stuff with iOS 7 so, if you support iOS 7, you will need to do stuff like ensure the autoresizingMask is set on the cell's contentView and that the contentView's bounds is set as the cell's bounds when the cell is loaded (i.e. awakeFromNib
).
Things you do need to be aware of is that your cell needs to be more seriously constrained than a Table View Cell. For instance, if you want your width to be dynamic then your cell needs a height constraint. Likewise, if you want the height to be dynamic then you will need a width constraint to your cell.
Implement preferredLayoutAttributesFittingAttributes
in your custom cell
When this function is called your view has already been configured with content (i.e. cellForItem
has been called). Assuming your constraints have been appropriately set you could have an implementation like this:
//forces the system to do one layout pass
var isHeightCalculated: Bool = false
override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
//Exhibit A - We need to cache our calculation to prevent a crash.
if !isHeightCalculated {
setNeedsLayout()
layoutIfNeeded()
let size = contentView.systemLayoutSizeFitting(layoutAttributes.size)
var newFrame = layoutAttributes.frame
newFrame.size.width = CGFloat(ceilf(Float(size.width)))
layoutAttributes.frame = newFrame
isHeightCalculated = true
}
return layoutAttributes
}
NOTE On iOS 9 the behaviour changed a bit that could cause crashes on your implementation if you are not careful (See more here). When you implement preferredLayoutAttributesFittingAttributes
you need to ensure that you only change the frame of your layout attributes once. If you don't do this the layout will call your implementation indefinitely and eventually crash. One solution is to cache the calculated size in your cell and invalidate this anytime you reuse the cell or change its content as I have done with the isHeightCalculated
property.
Experience your layout
At this point you should have 'functioning' dynamic cells in your collectionView.
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