UICollectionView's cellForItemAtIndexPath is not being called

Question

Only my second time using UICollectionView's and perhaps I have bitten off more than I can chew but nevertheless:

I am implementing a UICollectionView (myCollectionView) that uses custom UICollectionViewCell's that I have subclassed. The subclassed cells (FullReceiptCell) contain UITableView's and are the size of the viewcontroller. I am trying to allow for horizontal scrolling between the FullReceiptCells.

The subclassed UICollectionViewController that contains myCollectionView is being pushed on to a nav controller stack. Currently, myCollectionView loas and horizontal scrolling is enabled. However, no cells are visible. I have confirmed that

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section

has run and is returning an integer greater than 0. I have also confirmed that myCollectionView's delegate and datasource are properly set in IB to the subclassed UICollectionViewController.

The method where the cells are to be loaded:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

is not being called.

Here is where I push the UICollectionViewController and my viewDidLoad method within that controller (NOTE: initWithBill is an override of the normal initializer):

In the prior ViewControllers .m file:

FullReceiptViewController *test = [[FullReceiptViewController alloc] initWithBill:currentBill];
test.title = @"Review";
[self.navigationController pushViewController:test animated:YES];

In FullReceiptViewController.m:

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
    [self.myCollectionView registerClass:[FullReceiptCell class] forCellWithReuseIdentifier:@"FullReceiptCellIdentifier"];
    self.myCollectionView.pagingEnabled = YES;
    // Setup flowlayout

    self.myCollectionViewFlowLayout = [[UICollectionViewFlowLayout alloc] init];
    [self.myCollectionViewFlowLayout setItemSize:CGSizeMake(320, 548)];
    [self.myCollectionViewFlowLayout setSectionInset:UIEdgeInsetsMake(0, 0, 0, 0)];
    [self.myCollectionViewFlowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
    self.myCollectionViewFlowLayout.minimumLineSpacing = 0;
    self.myCollectionViewFlowLayout.minimumInteritemSpacing = 0;
    [self.myCollectionView setCollectionViewLayout:myCollectionViewFlowLayout];
    //testing to see if the collection view is loading
    self.myCollectionView.backgroundColor = [UIColor colorWithWhite:0.25f alpha:1.0f];

Any clue as to why it is not being called?

I am using XIB. I can't dequeue anything in cellForItemsAtIndexPath because it never gets called. — IkegawaTaro, Feb 03 '13 at 08:20

score 140 · Accepted Answer · answered Feb 04 '13 at 07:17

140

For those who stumble here later.... the reason:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath

was not being called was because of the itemSize for the collectionViewFlowLayout's height was too big.

[self.myCollectionViewFlowLayout setItemSize:CGSizeMake(320, 548)];

If I change the height to 410, it will execute cellForItemAtIndexPath.

answered Feb 04 '13 at 07:17

IkegawaTaro

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Can you elaborate a bit more. Same is happening for me – user1010819 Oct 15 '13 at 17:32
I just discovered that you need to be careful with collectionViewContentSize, too – Dimitar Marinov Feb 01 '14 at 15:14
51

In case you are using autolayout - be sure to set a height constraint on the collectionView - wasted many hours on this! – bpn Feb 21 '14 at 17:44
for the record height constrain didn't work for me.. horizontal center constrains did the trick – Mohamed Emad Hegab Nov 02 '14 at 19:09
Strangely, normally the layout will complain if you set the item size to something that doesn't fit, but in my case that didn't happen either; this is a very good observation :) – Ja͢ck Feb 13 '15 at 03:35
@bpn, How to set a constraint to the `UICollectionView` if it's the top-level view? – Iulian Onofrei Nov 26 '15 at 09:08
4

If your collectionView is constrained to topLayoutGuide with AutoLayout, and is not supposed to scroll under NavigationBar, make sure to uncheck `Adjust Scroll View Insets` on your ViewController on Storyboard. – Bruno Galinari Apr 15 '16 at 14:19
When the size of a whole section is CGRectZero, the collection view failed to load any cells. – ZhangChn Nov 28 '16 at 04:48
This worked for me but I am still oblivious as to why it works. hmmm. – maxcodes Apr 19 '17 at 21:27
In fact, you setting `flowLayout.itemSize` just gives its contentSize a non-zero value, which is final cause. – DawnSong Aug 16 '17 at 10:52
@bpn should have posted this as an answer, just saw your comment after figuring out :) – AamirR Nov 27 '17 at 11:19

esilver · Answer 2 · 2016-02-12T19:43:24.387

100

In my case, it was because my layout class incorrectly subclassed from UICollectionViewLayout instead of UICollectionViewFlowLayout

edited Feb 12 '16 at 19:43

answered Aug 20 '14 at 22:32

esilver

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This was my issue as well! It's a little counterintuitive, so it didn't even occur to me. Thanks for this! – WendiKidd Feb 12 '16 at 17:43
Same for me! its so easy to overlook that! thanks again – arvidurs Sep 06 '16 at 21:53
Facepalm here, thank you for pointing this out (4 years ago). – Milander Aug 08 '18 at 15:18
I was facing the same issue. Thanks – Piyush Gupta Dec 24 '18 at 15:39

score 33 · Answer 3 · answered Jul 22 '14 at 09:59

33

The cellForItemAtIndexPath will not get called if you do not provide the content size information to collection view.

If you are using Flow layout: You need to set the item sizes properly.
If you have a custom layout subclassed from UICollectionViewLayout: Ensure you are returning a proper size from the collectionViewContentSize method.

In case of the latter, you will also observe that your layoutAttributesForElementsRect is also not called. The reason is that you have not specified what is your content size and by default the size will be CGSizeZero. This basically tell collection view that you don't have any content to paint so it does not bother asking you for attributes or cells.

So, just override collectionViewContentSize and provide a proper size there, it should solve your problem.

answered Jul 22 '14 at 09:59

Deepak G M

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For example to use the full available size, return collectionView.frame.size from collectionViewContentSize (not simply collectionView.contentSize which defaults to 0, 0) – Adam Loving Apr 14 '15 at 17:44
Thanks! This answer helped me b/c I have a custom UICollectionViewLayout. If I started up the app in simulator in landscape orientation, some cells were not appearing in the initial view. Overriding the content size fixed this problem for me. – Chris Livdahl Apr 12 '17 at 05:24
1

Thank you. In my case the `collectionViewContentSize` incorrectly returned 0 for the width, that's why the `cellForItemAtIndexPath` was not getting called. – izerik Mar 22 '18 at 13:52

score 17 · Answer 4 · answered Jan 08 '16 at 08:34

17

For a more complicated view hierachy please check this blog. It saved my life!

self.automaticallyAdjustsScrollViewInsets = NO;

answered Jan 08 '16 at 08:34

Jaybo

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I spent so much time on this - and it all came down to that. If using storyboard or XIB, look at the parent view controller and deselect "Adjust Scroll View Insets" in the Attribute Inspector which is turned on by default. I tried all the other answers and they didn't work, it came down to this. – etayluz Mar 29 '16 at 21:03

score 16 · Answer 5 · answered Feb 03 '13 at 02:20

16

Maybe I'm just overlooking it, but it appears your missing your delegate and data source. In your header file, make sure you have added these:

<UICollectionViewDelegate, UICollectionViewDataSource>

and in your viewDidLoad method add this:

self.myCollectionView.delegate = self;
self.myCollectionView.dataSource = self;

Also, if you are loading it via an .xib, make sure you are have connected the IBOutlet to the UICollectionView.

answered Feb 03 '13 at 02:20

Anthony Castelli

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I didn't show it but I already have the delegate and datasource noted in the header file. Additionally, I have wired the IBOutlet to myCollectionView. The delegate and datasource for this collectionview have been set to FullReceiptViewController. The strange thing is that numberOfItemsInSection (a datasource protocol method) is getting called and returning an integer greater than 0. – IkegawaTaro Feb 03 '13 at 08:31
Hmm, When you launch the application does the Collection view show or do anything? It sounds like it does have some items in it if numberOfItemsInSection returns something greater than 0. – Anthony Castelli Feb 04 '13 at 00:46
Thanks for following up. The collectionview does show... I can tell because I changed the background color. I believe I have found the problem: [self.myCollectionViewFlowLayout setItemSize:CGSizeMake(320, 548)]; This was too big. If I decrease the height to 410, I can get the cellForItemAtIndexPath method to be called. – IkegawaTaro Feb 04 '13 at 07:13
@AnthonyCastelli Hello,I am also facing the same issue, numberOfItemsInSection being called on pop to viewController but not cellForItemsAtIndexPath. so do you get the clue? – Bhavin Kansagara Nov 24 '13 at 08:01

Gurjinder Singh · Answer 6 · 2018-06-12T10:55:54.633

15

If your class is subclass from UICollectionviewController and you are creating collectionView programmatically then use

let layout = UICollectionViewFlowLayout()
    layout.scrollDirection = .Vertical
    layout.itemSize = CGSizeMake(50, 50)

    collectionView?.setCollectionViewLayout(layout, animated: false)

edited Jun 12 '18 at 10:55

answered Jan 30 '17 at 14:56

Gurjinder Singh

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This is the answer solved my problem! The override method func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize { } does not work for me. – Mike Feb 23 '19 at 19:15

score 10 · Answer 7 · answered Nov 27 '17 at 11:20

10

I was using autolayout, and in my case height constraint was missing

answered Nov 27 '17 at 11:20

AamirR

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score 6 · Answer 8 · answered Sep 07 '17 at 17:52

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My issue was that I had 2 collection views within the same view, and both were sharing a computed UICollectionViewFlowLayout instance. Once I created separate instances of the same flow layout, it worked fine.

answered Sep 07 '17 at 17:52

nebyark

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score 5 · Answer 9 · edited Feb 05 '14 at 08:04

5

In my case, what I had very stupidly forgotten to do was implement the UICollectionViewDataSource protocol method numberOfItemsInSection, so that is another thing to check.

edited Feb 05 '14 at 08:04

Marius

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answered Feb 05 '14 at 07:41

Dean

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score 5 · Answer 10 · answered May 17 '17 at 00:30

5

Also, make sure that reloadData is not called while collection view is updating with animation (insert, delete, update or performBatchUpdates).

answered May 17 '17 at 00:30

sasha_nec

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The tricky part is how to actually do this... – algrid Nov 27 '20 at 15:59

6david9 · Answer 11 · 2017-05-19T02:42:55.717

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In my case, set collectionView.prefetchingEnabled = NO; solved my problem. Only works on iOS 10.

edited May 19 '17 at 02:42

answered May 19 '17 at 02:25

6david9

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I upvoted that answer some time ago and today it helped me again :D You deserve a Noble for this answer man. Thanks again! – Maciek Czarnik Apr 23 '20 at 09:36
this answer worked for me! I wish there was an explanation as to why included with it because I never had it set to true to begin with. – Lance Samaria Jun 07 '20 at 22:48

score 3 · Answer 12 · answered Nov 20 '13 at 13:36

3

It was happening for me when item height == 0 by fixing that cellForItem method was called.

answered Nov 20 '13 at 13:36

Jirune

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score 3 · Answer 13 · answered Apr 18 '15 at 08:01

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Ten minutes ago I also encountered this problem, I made a silly mistake.

My intention is to use UICollectionViewFlowLayout,

But because of mistakes, I used UICollectionViewLayout.

answered Apr 18 '15 at 08:01

Vincent Sit

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score 3 · Answer 14 · answered Sep 02 '15 at 08:03

3

In my case, changing UINavigationBar's translucent to NO solved the problem.

answered Sep 02 '15 at 08:03

chanil

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score 3 · Answer 15 · answered Oct 29 '15 at 07:15

In Xcode 7.0.1, we got this problem when we copied a storyboard and accompanying code from another project. The collection view had a custom flow layout set in the storyboard. Solution was to:

Remove the flow layout in IB
Compile/run the app
Set the flow layout back

Now it worked :)

score 3 · Answer 16 · edited Mar 02 '16 at 19:43

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I forgot to set the autoresizing mask to false on the collection view:

collectionView.translatesAutoresizingMaskIntoConstraints = false

edited Mar 02 '16 at 19:43

Undo

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answered Mar 02 '16 at 18:58

Stritt

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score 3 · Answer 17 · answered Oct 10 '18 at 14:43

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In storyboard/xib UICollectionView property cellSize MUST not be {0, 0}

answered Oct 10 '18 at 14:43

poGUIst

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score 3 · Answer 18 · answered May 04 '20 at 16:01

3

In my case I had the collectionView in a UIStackView with alignment = .center. So the collectionView did not have a width. When setting the stackView.alignment to .fill everything was fine.

answered May 04 '20 at 16:01

Nico S.

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score 2 · Answer 19 · answered Jan 13 '15 at 18:51

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Make sure numberOfSectionsInCollectionView returns a positive integer as well.

There has to be at least one section in the collection.

answered Jan 13 '15 at 18:51

Eran Goldin

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score 2 · Answer 20 · answered Jan 30 '15 at 21:48

2

Make sure -(NSInteger) collectionView:numberOfItemsInSection: is returning a positive (read, greater than zero) value. It may be a matter of placing [self.collectionView reloadData]; in the completion handler.

answered Jan 30 '15 at 21:48

RT Denver

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score 2 · Answer 21 · edited Oct 05 '19 at 04:12

2

If you're using collection view protocols you must connect the CollectionViewDataSource and CollectionViewDelegate protocols to your ViewController.

edited Oct 05 '19 at 04:12

Marcus Adams

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answered Mar 28 '17 at 11:40

Declan McKenna

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score 2 · Answer 22 · answered Nov 01 '17 at 09:52

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It can be realated layout problems. Check layout warnings from console, if exist.

answered Nov 01 '17 at 09:52

erdikanik

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score 2 · Answer 23 · answered Dec 06 '17 at 10:21

2

In my case the collection view was not fully visible in its parent view due to wrong auto layout constraints. So fixing the constraints made the collection view all visible and cellForItemAtIndexPath was called.

answered Dec 06 '17 at 10:21

Khaled Annajar

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score 1 · Answer 24 · answered Nov 01 '14 at 03:35

1

Same happened to me. I had 2 UICollectionViews and I removed once since I didn't need that. After that I realised that the CellForItemAtIndexPath was not getting called but the other required methods. I tried all of the above but then I did the standard magic. Removed the collection view from storyboard and added again. Then it started working. Not sure why and I have no explanation but maybe some connection issues.

answered Nov 01 '14 at 03:35

Hafeez

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I copied my UICollectionView from another UIViewController in storyboard. I deleted the the CollectionView and added again to make it work. Thank you for your answer. – Drunken Daddy Jan 24 '17 at 14:00

score 1 · Answer 25 · answered Jul 16 '17 at 00:34

Just resolved this issue, for a somewhat specific situation.

In my case, I was manually initializing the UICollectionViewController in a parent ViewController, and then adding the UICollectionViewController's view as a subview.

I resolved the issue by calling 'setNeedsLayout' and/or 'setNeedsDisplay' on the collectionView in the parent's viewDidAppear:

- (void)viewDidAppear:(BOOL)animated {
   [super viewDidAppear:animated];
   [_collection.view setNeedsLayout];
   [_collection.view setNeedsDisplay];
}

score 1 · Answer 26 · answered Oct 19 '17 at 09:50

When using UICollectionViewDelegateFlowLayout be careful on what this function returns. Both width and height should be greater than 0. I used window as frame reference but due to complicated view hierarchy window was nil at runtime. If you need adjust the width of the element based on screen width use UIScreen.main.bounds.

func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: 
           UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {}

score 1 · Answer 27 · answered Apr 18 '20 at 06:42

I was having a similar problem. But instead cellForItemAtIndexPath was called when the number of items was > 1, but not when there was only a single item. I tried many of the proposed solutions here and similar to many I found that it had to do with item sizing. For me the solution was to change the estimate size of the UICollectionView from Automatic to Custom.

score 0 · Answer 28 · answered Jun 13 '17 at 13:42

For me, I update the height of self.view (the collectionView's superview) via autolayout, and MUST call layoutIfNeeded after that.

[self.view mas_updateConstraints:^(MASConstraintMaker *make) {
    make.height.equalTo(@(height));
}];
[self.view layoutIfNeeded];

score 0 · Answer 29 · answered Dec 19 '19 at 09:22

In my case I had to adjust the estimated Content size. content size did not do it.

  let layout = collectionVC.collectionView.collectionViewLayout as! UICollectionViewFlowLayout
    layout.itemSize = CGSize(width: 100, height: 100)
    layout.estimatedItemSize = CGSize(width: 100, height: 100)

score -1 · Answer 30 · answered Jan 20 '16 at 00:34

I sunk a bit of time with this issue coming op with a CollectionView in a Contained view controller loaded from a storyboard. I ended up just deleting the contained view controller, and recreating it in the storyboard, and this seemed to get rid of the issue. My guess is there was some kind of storyboard corruption that had taken place.

score -2 · Answer 31 · answered Dec 25 '15 at 11:42

-2

Setting collectionView frame inside custom cell's layoutSubViews() worked for me:

override func layoutSubviews() {
        super.layoutSubviews()
        let frame = self.contentView.bounds
        self.CollectionView.frame = frame
    }

answered Dec 25 '15 at 11:42

Javal Nanda

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UICollectionView's cellForItemAtIndexPath is not being called

31 Answers31

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