I am trying to implement a collection view, in which items have:
automatic height based on constraints
the full available width of the collection view.
I'm aware that this is pretty easy to accomplish UICollectionViewCompositionalLayout, but I'm looking to solve it for iOS 11+. I've decided to implement a custom UICollectionViewFlowLayout:
class SingleColumnFlowLayout: UICollectionViewFlowLayout {
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]? {
guard let collectionView = collectionView,
let layoutAttributes = super.layoutAttributesForElements(in: rect) else { return [] }
layoutAttributes
.filter { $0.representedElementCategory == .cell }
.forEach { attributes in
let availableWidth = collectionView.bounds
.inset(by: collectionView.contentInset)
.width
attributes.frame.origin.x = sectionInset.left
attributes.frame.size.width = availableWidth
}
return layoutAttributes
}
}
The result isn't quite what I have imagined:
The cell I'm using is pretty simple:
Interestingly if I add a fixed width constraint to the label, it works correctly, so my theory is that
for some reason the collection view fails to infer the width of the label correctly
for that reason, it thinks that it can fit multiple items in the same row
because of this, it calculates incorrect y values for some of the items.
I would like to make this work without fixed-width labels, so my question would be: am I missing anything obvious? Is there a way to fix this?
For anyone interested, I've uploaded the entire project to GitHub.
As it turns out, the issue was caused by the fixed trailing constraint of the label. The label's intrinsic width was smaller (due to short text), and since the entire cell was constrained horizontally, the cell width also became small. I fixed it by changing the trailing constraint from 'equal' to 'greater than'.
I'm trying to build something
I'm trying to build a tag list view using UICollectionView and nest it into my custom UITableViewCell.
What do I have now
After searching the internet, I find the key to the problem:
Subclass UICollectionView and implement it's intrinsic content size property.
However, when I nest my custom UICollectionView into a self-sizing UITableViewCell, the whole thing doesn't work well. The layout is broken.
No matter how do I change the code, I get one of the following 3 buggy UIs.
The height of the collection view is always wrong, either too small or too large, it can not hug it's content just right.
When I use Debug View Hierarchy to check the views, I find that although the UI is broken, the contentSize property of the collection view has a correct value. It seems that the content size property can not be reflected to the UI in time.
class IntrinsicCollectionView: UICollectionView {
override var contentSize: CGSize {
didSet {
invalidateIntrinsicContentSize()
}
}
override var intrinsicContentSize: CGSize {
layoutIfNeeded()
return CGSize(width: UIView.noIntrinsicMetric, height: collectionViewLayout.collectionViewContentSize.height)
}
override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
super.init(frame: frame, collectionViewLayout: layout)
isScrollEnabled = false
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
There are many solution about how to create a custom UICollectionView with intrinsic content size. Some of them can work correctly. But when nesting them into a UITableViewCell, none of them works well.
There are also some answer about just nest one UICollectionView into UITableViewCell without other views. But if there are also some UILabel in UITableViewCell, it won't work.
I upload all the code to github. https://github.com/yunhao/nest-collectionview-in-tableviewcell
Thank you!
I'll try to explain what's going on....
To make it easy to understand, in your ListViewController let's work with just one row to begin with:
override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return 1 // items.count
}
In your ListViewCell class, add these lines at the end of prepareViews():
// so we can see the element frames
titleLabel.backgroundColor = .green
subtitleLabel.backgroundColor = .cyan
collectionView.backgroundColor = .yellow
In your IntrinsicCollectionView class, let's add a print() statement to give us some information:
override var intrinsicContentSize: CGSize {
layoutIfNeeded()
// add this line
print("collView Width:", frame.width, "intrinsic height:", collectionViewLayout.collectionViewContentSize.height)
return CGSize(width: UIView.noIntrinsicMetric, height: collectionViewLayout.collectionViewContentSize.height)
}
When I then run the app on an iPhone 8, I get this result:
and I see this in the debug console:
collView Width: 66.0 intrinsic height: 350.0
collView Width: 343.0 intrinsic height: 30.0
What that tells me is that the collection view is asked for its intrinsicContentSize before it has a complete frame.
At that point, it fills in its cells, and its layout ends up with a .collectionViewContentSize.height of 350 (this row has six "tags" cells).
Auto-layout then performs another pass... the collection view now has a valid frame width (based on the cell width)... and the cells are re-laid-out.
Unfortunately, the table view has already set the row height(s), based on the initial collection view intrinsicContentSize.height.
So, two steps that may (should) fix this:
In ListViewCell, invalidate the content size of the collection view when you get the tags:
func setTags(_ tags: [String]) {
self.tags = tags
collectionView.reloadData()
// add this line
collectionView.invalidateIntrinsicContentSize()
}
Then, in ListViewController, we need to reload the table after its frame has changed:
// add this var
var currentWidth: CGFloat = 0
// implement viewDidLayoutSubviews()
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
if view.frame.width != currentWidth {
currentWidth = view.frame.width
tableView.reloadData()
}
}
That seems (with very quick testing) to give me reliable results:
and on device rotation:
I have a UICollectionView that holds a bunch of a photos.
However, if I scroll to the bottom the scrollview does not let me scroll to the bottom of the last few rows (it snaps back). I have tried override the collectionView.contentSize and just adding 1000 to the height but it doesn't fix the problem.
collectionView.contentSize = CGSizeMake(collectionView.contentSize.width, collectionView.contentSize.height + 1000)
Here is a video of the problem:
https://www.youtube.com/watch?v=fH57_pL0OjQ&list=UUIctdpq1Pzujc0u0ixMSeVw
Here is my code to create cells:
func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell
{
var cell = collectionView.dequeueReusableCellWithReuseIdentifier("selectPhotoCell", forIndexPath: indexPath) as B_SelectPhotoControllerViewCell
let reuseCount = ++cell.reuseCount
let asset = currentAssetAtIndex(indexPath.item)
PHImageManager.defaultManager().requestImageForAsset(asset, targetSize:_cellSize, contentMode: .AspectFit, options: nil)//the target size here can be set to CGZero for a super blurry preview
{
result, info in
if reuseCount == cell.reuseCount
{
cell.imageView.image = result
cell.imageView.frame = CGRectMake(0, 0,self._cellSize.width,self._cellSize.height)
}
}
return cell
}
private func currentAssetAtIndex(index:NSInteger)->PHAsset
{
if let fetchResult = _assetsFetchResults
{
return fetchResult[index] as PHAsset
}else
{
return _selectedAssets[index]
}
}
Update:
Because I am adding this as a child view controller, there seems to be some problems with the offsetting of the scrollview. I haven't fixed it yet but when open this view without adding it as a child view to another view controller, the scrollview is the correct size
The problem was I was adding this as a child view controller.
As a result, after doing some animations, the UICollectionView bounds were sizing to the view it was attached to. As a result its height was wrong and hence why it was getting cut off.
I just came across this question from a quick Google and felt I could add something useful.
I am running a segmentedControl with a UIView that changes to different UICollectionViews on the segment change and I couldn't get the collectionView to scroll fully down.
This may not be the solution for all, but I found that if I went to the XIB I was loading in the view and set size to freeform and decrease it by the size of a cell I had removed the problem.
suspect your CollectionView's bottomAchor was not set correctly to the parent uiview's safeAreaLayoutGuide bottomAnchor
I'm trying to get self sizing UICollectionViewCells working with Auto Layout, but I can't seem to get the cells to size themselves to the content. I'm having trouble understanding how the cell's size is updated from the contents of what's inside the cell's contentView.
Here's the setup I've tried:
Custom UICollectionViewCell with a UITextView in its contentView.
Scrolling for the UITextView is disabled.
The contentView's horizontal constraint is: "H:|[_textView(320)]", i.e. the UITextView is pinned to the left of the cell with an explicit width of 320.
The contentView's vertical constraint is: "V:|-0-[_textView]", i.e. the UITextView pinned to the top of the cell.
The UITextView has a height constraint set to a constant which the UITextView reports will fit the text.
Here's what it looks like with the cell background set to red, and the UITextView background set to Blue:
I put the project that I've been playing with on GitHub here.
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. I haven't yet found the out-of-the box solution sufficient during my tests so feel free to comment if you have. It still feels like UITableView wins the battle for dynamic sizing IMHO.
##Caveats
Be very mindful that if you are using prototype cells to calculate the estimatedItemSize - this will break if your XIB uses size classes. The reason for this is that when you load your cell from a XIB its size class will be configured with Undefined. This will only be broken on iOS 8 and up since on iOS 7 the size class will be loaded based on the device (iPad = Regular-Any, iPhone = Compact-Any). You can either set the estimatedItemSize without loading the XIB, or you can load the cell from the XIB, add it to the collectionView (this will set the traitCollection), perform the layout, and then remove it from the superview. Alternatively you could also make your cell override the traitCollection getter and return the appropriate traits. It's up to you.
In iOS10 there is new constant called UICollectionViewFlowLayout.automaticSize (formerly UICollectionViewFlowLayoutAutomaticSize), so instead:
self.flowLayout.estimatedItemSize = CGSize(width: 100, height: 100)
you can use this:
self.flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
It has better performance especially when cells in your collection view have constant width.
Accessing Flow Layout:
override func viewDidLoad() {
super.viewDidLoad()
if let flowLayout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
}
}
Swift 5 Updated:
override func viewDidLoad() {
super.viewDidLoad()
if let flowLayout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
}
}
A few key changes to Daniel Galasko's answer fixed all my problems. Unfortunately, I don't have enough reputation to comment directly (yet).
In step 1, when using Auto Layout, simply add a single parent UIView to the cell. EVERYTHING inside the cell must be a subview of the parent. That answered all of my problems. While Xcode adds this for UITableViewCells automatically, it doesn't (but it should) for UICollectionViewCells. According to the docs:
To configure the appearance of your cell, add the views needed to present the data item’s content as subviews to the view in the contentView property. Do not directly add subviews to the cell itself.
Then skip step 3 entirely. It isn't needed.
In iOS 10+ this is a very simple 2 step process.
Ensure that all your cell contents are placed within a single UIView (or inside a descendant of UIView like UIStackView which simplifies autolayout a lot). Just like with dynamically resizing UITableViewCells, the whole view hierarchy needs to have constraints configured, from the outermost container to the innermost view. That includes constraints between the UICollectionViewCell and the immediate childview
Instruct the flowlayout of your UICollectionView to size automatically
yourFlowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
Add flowLayout on viewDidLoad()
override func viewDidLoad() {
super.viewDidLoad()
if let flowLayout = infoCollection.collectionViewLayout as? UICollectionViewFlowLayout {
flowLayout.estimatedItemSize = CGSize(width: 1, height:1)
}
}
Also, set an UIView as mainContainer for your cell and add all required views inside it.
Refer to this awesome, mind-blowing tutorial for further reference:
UICollectionView with autosizing cell using autolayout in iOS 9 & 10
EDIT 11/19/19: For iOS 13, just use UICollectionViewCompositionalLayout with estimated heights. Don't waste your time dealing with this broken API.
After struggling with this for some time, I noticed that resizing does not work for UITextViews if you don't disable scrolling:
let textView = UITextView()
textView.scrollEnabled = false
contentView anchor mystery:
In one bizarre case this
contentView.translatesAutoresizingMaskIntoConstraints = false
would not work. Added four explicit anchors to the contentView and it worked.
class AnnoyingCell: UICollectionViewCell {
#IBOutlet var word: UILabel!
override init(frame: CGRect) {
super.init(frame: frame); common() }
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder); common() }
private func common() {
contentView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
contentView.leftAnchor.constraint(equalTo: leftAnchor),
contentView.rightAnchor.constraint(equalTo: rightAnchor),
contentView.topAnchor.constraint(equalTo: topAnchor),
contentView.bottomAnchor.constraint(equalTo: bottomAnchor)
])
}
}
and as usual
estimatedItemSize = UICollectionViewFlowLayout.automaticSize
in YourLayout: UICollectionViewFlowLayout
Who knows? Might help someone.
Credit
https://www.vadimbulavin.com/collection-view-cells-self-sizing/
stumbled on to the tip there - never saw it anywhere else in all the 1000s articles on this.
I did a dynamic cell height of collection view. Here is git hub repo.
And, dig out why preferredLayoutAttributesFittingAttributes is called more than once. Actually, it will be called at least 3 times.
The console log picture :
1st preferredLayoutAttributesFittingAttributes:
(lldb) po layoutAttributes
<UICollectionViewLayoutAttributes: 0x7fa405c290e0> index path: (<NSIndexPath: 0xc000000000000016>
{length = 2, path = 0 - 0}); frame = (15 12; 384 57.5);
(lldb) po self.collectionView
<UICollectionView: 0x7fa40606c800; frame = (0 57.6667; 384 0);
The layoutAttributes.frame.size.height is current status 57.5.
2nd preferredLayoutAttributesFittingAttributes:
(lldb) po layoutAttributes
<UICollectionViewLayoutAttributes: 0x7fa405c16370> index path: (<NSIndexPath: 0xc000000000000016>
{length = 2, path = 0 - 0}); frame = (15 12; 384 534.5);
(lldb) po self.collectionView
<UICollectionView: 0x7fa40606c800; frame = (0 57.6667; 384 0);
The cell frame height changed to 534.5 as our expected. But, the collection view still zero height.
3rd preferredLayoutAttributesFittingAttributes:
(lldb) po layoutAttributes
<UICollectionViewLayoutAttributes: 0x7fa403d516a0> index path: (<NSIndexPath: 0xc000000000000016>
{length = 2, path = 0 - 0}); frame = (15 12; 384 534.5);
(lldb) po self.collectionView
<UICollectionView: 0x7fa40606c800; frame = (0 57.6667; 384 477);
You can see the collection view height was changed from 0 to 477.
The behavior is similar to handle scroll:
1. Before self-sizing cell
2. Validated self-sizing cell again after other cells recalculated.
3. Did changed self-sizing cell
At beginning, I thought this method only call once. So I coded as the following:
CGRect frame = layoutAttributes.frame;
frame.size.height = frame.size.height + self.collectionView.contentSize.height;
UICollectionViewLayoutAttributes* newAttributes = [layoutAttributes copy];
newAttributes.frame = frame;
return newAttributes;
This line:
frame.size.height = frame.size.height + self.collectionView.contentSize.height;
will cause system call infinite loop and App crash.
Any size changed, it will validate all cells' preferredLayoutAttributesFittingAttributes again and again until every cells' positions (i.e frames) are no more change.
In addition to above answers,
Just make sure you set estimatedItemSize property of UICollectionViewFlowLayout to some size and do not implement sizeForItem:atIndexPath delegate method.
That's it.
The solution comprises 3 simple steps:
Enabling dynamic cell sizing
flowLayout.estimatedItemSize = UICollectionViewFlowLayout.automaticSize
Set the containerView.widthAnchor.constraint from collectionView(:cellForItemAt:)to limit the width of contentView to width of collectionView.
class ViewController: UIViewController, UICollectionViewDataSource {
...
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellId", for: indexPath) as! MultiLineCell
cell.textView.text = dummyTextMessages[indexPath.row]
cell.maxWidth = collectionView.frame.width
return cell
}
...
}
class MultiLineCell: UICollectionViewCell{
....
var maxWidth: CGFloat? {
didSet {
guard let maxWidth = maxWidth else {
return
}
containerViewWidthAnchor.constant = maxWidth
containerViewWidthAnchor.isActive = true
}
}
....
}
Since you want to enable self-sizing of UITextView, it has an additional step to;
3. Calculate and set the heightAnchor.constant of UITextView.
So, whenever the width of contentView is set we'll adjust height of UITextView along in didSet of maxWidth.
Inside UICollectionViewCell:
var maxWidth: CGFloat? {
didSet {
guard let maxWidth = maxWidth else {
return
}
containerViewWidthAnchor.constant = maxWidth
containerViewWidthAnchor.isActive = true
let sizeToFitIn = CGSize(width: maxWidth, height: CGFloat(MAXFLOAT))
let newSize = self.textView.sizeThatFits(sizeToFitIn)
self.textViewHeightContraint.constant = newSize.height
}
}
These steps will get you the desired result.
Complete runnable gist
Reference: Vadim Bulavin blog post - Collection View Cells Self-Sizing: Step by Step Tutorial
Screenshot:
If you implement UICollectionViewDelegateFlowLayout method:
- (CGSize)collectionView:(UICollectionView*)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath*)indexPath
When you call collectionview performBatchUpdates:completion:, the size height will use sizeForItemAtIndexPath instead of
preferredLayoutAttributesFittingAttributes.
The rendering process of performBatchUpdates:completion will go through the method preferredLayoutAttributesFittingAttributes but it ignores your changes.
To whomever it may help,
I had that nasty crash if estimatedItemSize was set. Even if I returned 0 in numberOfItemsInSection. Therefore, the cells themselves and their auto-layout were not the cause of the crash... The collectionView just crashed, even when empty, just because estimatedItemSize was set for self-sizing.
In my case I reorganized my project, from a controller containing a collectionView to a collectionViewController, and it worked.
Go figure.
For anyone who tried everything without luck, this is the only thing that got it working for me.
For the multiline labels inside cell, try adding this magic line:
label.preferredMaxLayoutWidth = 200
More info: here
Cheers!
The example method above does not compile. Here is a corrected version (but untested as to whether or not it works.)
override func preferredLayoutAttributesFittingAttributes(layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes
{
let attr: UICollectionViewLayoutAttributes = layoutAttributes.copy() as! UICollectionViewLayoutAttributes
var newFrame = attr.frame
self.frame = newFrame
self.setNeedsLayout()
self.layoutIfNeeded()
let desiredHeight: CGFloat = self.contentView.systemLayoutSizeFittingSize(UILayoutFittingCompressedSize).height
newFrame.size.height = desiredHeight
attr.frame = newFrame
return attr
}
Update more information:
If you use flowLayout.estimatedItemSize, suggest use iOS8.3 later version. Before iOS8.3, it will crash [super layoutAttributesForElementsInRect:rect];.
The error message is
*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSArrayM insertObject:atIndex:]: object cannot be nil'
Second, in iOS8.x version, flowLayout.estimatedItemSize will cause different section inset setting did not work. i.e. function: (UIEdgeInsets)collectionView:layout:insetForSectionAtIndex:.
I tried using estimatedItemSize but there were a bunch of bugs when inserting and deleting cells if the estimatedItemSize was not exactly equal to the cell's height. i stopped setting estimatedItemSize and implemented dynamic cell's by using a prototype cell. here's how that's done:
create this protocol:
protocol SizeableCollectionViewCell {
func fittedSize(forConstrainedSize size: CGSize)->CGSize
}
implement this protocol in your custom UICollectionViewCell:
class YourCustomCollectionViewCell: UICollectionViewCell, SizeableCollectionViewCell {
#IBOutlet private var mTitle: UILabel!
#IBOutlet private var mDescription: UILabel!
#IBOutlet private var mContentView: UIView!
#IBOutlet private var mTitleTopConstraint: NSLayoutConstraint!
#IBOutlet private var mDesciptionBottomConstraint: NSLayoutConstraint!
func fittedSize(forConstrainedSize size: CGSize)->CGSize {
let fittedSize: CGSize!
//if height is greatest value, then it's dynamic, so it must be calculated
if size.height == CGFLoat.greatestFiniteMagnitude {
var height: CGFloat = 0
/*now here's where you want to add all the heights up of your views.
apple provides a method called sizeThatFits(size:), but it's not
implemented by default; except for some concrete subclasses such
as UILabel, UIButton, etc. search to see if the classes you use implement
it. here's how it would be used:
*/
height += mTitle.sizeThatFits(size).height
height += mDescription.sizeThatFits(size).height
height += mCustomView.sizeThatFits(size).height //you'll have to implement this in your custom view
//anything that takes up height in the cell has to be included, including top/bottom margin constraints
height += mTitleTopConstraint.constant
height += mDescriptionBottomConstraint.constant
fittedSize = CGSize(width: size.width, height: height)
}
//else width is greatest value, if not, you did something wrong
else {
//do the same thing that's done for height but with width, remember to include leading/trailing margins in calculations
}
return fittedSize
}
}
now make your controller conform to UICollectionViewDelegateFlowLayout, and in it, have this field:
class YourViewController: UIViewController, UICollectionViewDelegateFlowLayout {
private var mCustomCellPrototype = UINib(nibName: <name of the nib file for your custom collectionviewcell>, bundle: nil).instantiate(withOwner: nil, options: nil).first as! SizeableCollectionViewCell
}
it will be used as a prototype cell to bind data to and then determine how that data affected the dimension that you want to be dynamic
finally, the UICollectionViewDelegateFlowLayout's collectionView(:layout:sizeForItemAt:) has to be implemented:
class YourViewController: UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource {
private var mDataSource: [CustomModel]
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath)->CGSize {
//bind the prototype cell with the data that corresponds to this index path
mCustomCellPrototype.bind(model: mDataSource[indexPath.row]) //this is the same method you would use to reconfigure the cells that you dequeue in collectionView(:cellForItemAt:). i'm calling it bind
//define the dimension you want constrained
let width = UIScreen.main.bounds.size.width - 20 //the width you want your cells to be
let height = CGFloat.greatestFiniteMagnitude //height has the greatest finite magnitude, so in this code, that means it will be dynamic
let constrainedSize = CGSize(width: width, height: height)
//determine the size the cell will be given this data and return it
return mCustomCellPrototype.fittedSize(forConstrainedSize: constrainedSize)
}
}
and that's it. Returning the cell's size in collectionView(:layout:sizeForItemAt:) in this way preventing me from having to use estimatedItemSize, and inserting and deleting cells works perfectly.
In Swift 5, it works for me.
UICollectionViewFlowLayout:
estimatedItemSize = UICollectionViewFlowLayout.automaticSize
UICollectionViewCell:
(ps: I'm using SnapKit)
class Cell: UICollectionViewCell {
let customizedContentView = UIView()
...
func layoutAction() {
contentView.translatesAutoresizingMaskIntoConstraints = false
contentView.addSubview(customizedContentView)
customizedContentView.snp.makeConstraints { make in
make.edges.equalToSuperview()
}
}
}
then you just need to expand customizedContentView.
What is the best method to provide a footer for a UICollectionView that "sticks" to the bottom of the screen bounds on a given page? Assume the UICollectionView is full screen and only has one section.
Currently I am providing a UICollectionReusableView object in collectionView:viewForSupplementaryElementOfKind:atIndexPath:, but (as one might expect) when the content of my collection exceeds this screen's bounds, the footer is pushed off-screen.
I'm guessing the key is a Decoration View - but I can't find any good code (non-IB) examples on how these work, and Apple's documentation is in my opinion unclear on this particular subject.
Update re: Decoration Views
After building out and experimenting with a Decoration View (using this tutorial), I hit some limitations - namely that there aren't really any callbacks between the Decoration View object and your UICollectionViewController controller object (the Decoration View is managed by a UICollectionViewLayout object, not the UICollectionViewController object). It seems Apple was very serious about Decoration Views being limited to visual adornments, and not data-driven (although you could obviously hack around this).
So, the "right" solution still eludes me, but in the mean time I just created a static UIView object and am just managing that from my UICollectionViewController object. It works OK, but feels wrong.
Update re: Sticky HEADERS
Over the last few months, I've worked on similar issues across various projects, and did recently find a solution for sticky HEADERS. I assume the same would apply to footers, but I haven't tested it.
Details about headers here:
How to make Supplementary View float in UICollectionView as Section Headers do in UITableView plain style
The implementation is pretty heavy, but it seems to work well in most circumstances.
If there is no further activity on this question soon, I will close as a duplicate and point to the article above.
Basically what you need to do is provide a custom UICollectionViewLayout subclass that invalidates itself when the bounds change (when the view scrolls the bounds change). And then provides UICollectionViewLayoutAttributes for the supplementary view where the center is updated to hug the current bounds of the collection view (top, bottom, left, right, whatever).
I added project on github that demonstrates this strategy.
UPDATE: as of iOS 9, UICollectionViewFlowLayout has two very handy properties that simplify this task drastically. See sectionHeadersPinToVisibleBounds and sectionFootersPinToVisibleBounds.
ok.. so I have tried updating code from below link. and it works.
https://teamtreehouse.com/community/add-sticky-footer-to-uicollectionview-in-swift
class StickyFooter : UICollectionViewFlowLayout {
var footerIsFound : Bool = false
var UICollectionAttributes : [UICollectionViewLayoutAttributes]?
override func shouldInvalidateLayout(forBoundsChange newBounds: CGRect) -> Bool {
return true
}
override func layoutAttributesForElements(in rect: CGRect) -> [UICollectionViewLayoutAttributes]?
{
UICollectionAttributes = super.layoutAttributesForElements(in: rect)
for attributes in UICollectionAttributes! {
if let type = attributes.representedElementKind {
if type == UICollectionElementKindSectionFooter
{
footerIsFound = true
updateFooter(attributes: attributes)
}
}
}
if (!self.footerIsFound) {
let newItem = self.layoutAttributesForSupplementaryView(ofKind: UICollectionElementKindSectionFooter, at : NSIndexPath(row: self.UICollectionAttributes!.count, section: 0) as IndexPath)
UICollectionAttributes?.append(newItem!)
}
return UICollectionAttributes
}
override func layoutAttributesForSupplementaryView(ofKind elementKind: String, at indexPath: IndexPath) -> UICollectionViewLayoutAttributes?
{
let attributes = UICollectionViewLayoutAttributes(forSupplementaryViewOfKind: elementKind, with: indexPath)
attributes.size = CGSize(width: self.collectionView!.bounds.size.width, height: 75)
if elementKind.isEqualToString(find: UICollectionElementKindSectionFooter)
{
updateFooter(attributes: attributes)
}
return attributes
}
func updateFooter(attributes : UICollectionViewLayoutAttributes){
let currentBounds = self.collectionView?.bounds
attributes.zIndex = 1024
attributes.isHidden = false
let yOffset = currentBounds!.origin.y + currentBounds!.size.height - attributes.size.height/2.0
attributes.center = CGPoint(x: currentBounds!.midX, y: yOffset)
}}
UICollectionViewController (like UITableVC) is a "shortcut", these 2 classes are just overriding UIViewController, create the collectionView for you.
You can easily do that and add your sticky view on your own.