UICollectionView Self Sizing Cells with Auto Layout

Question

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

User · Answer

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.

User · Answer

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  - gt  UICollectionViewCell           let cell   collectionView dequeueReusableCell withReuseIdentifier   quot cellId quot   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

User · Answer

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 you collection view has constant wid  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

User · Answer

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

User · Answer

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

User · Answer

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  amp  10

User · Answer

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

User · Answer

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

User · Answer

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 - gt 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 - gt 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   lt name of the nib file for your custom collectionviewcell gt   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 - gt 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

User · Answer

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  - gt  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    Let me know if I missed anything  hope I helped and good luck coding

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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

User · Answer

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  - gt  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

User · Answer

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

[ios] UICollectionView Self Sizing Cells with Auto Layout

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