By Rui Peres


2012-11-13 12:42:02 8 Comments

What's happening

Currently I have an application that uses two UICollectionViews inside a UITableView. This way I create a Pulse News look like application. My problem with this is that sometimes the 6th and 11th row disappears completely, leaving a blank space where it should be the cell. I wouldn't actually mind, if all the cells were like this (and this way I could assume that I wasn't doing things correctly), but the thing is, is just happening with those specific ones.

My theory

The 6th and 11th rows are the ones that appears when I start scrolling, so by default I am able to see 5 cells, and when I do the first horizontal scrolling the 6th comes up (blank space sometimes).

What I have

The only thing I am doing at the moment is this:

 [self.collectionView registerNib:[UINib nibWithNibName:CELL_NIB_NAME bundle:nil] forCellWithReuseIdentifier:CELL_IDENTIFIER];

On the viewDidLoad. And on the creation of the cell:

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    MyCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CELL_IDENTIFIER forIndexPath:indexPath];

    NSMutableDictionary *dictionary = [self.DataSource objectAtIndex:[indexPath row]];

    [cell buildViewWithDictionary:dictionary withReferenceParent:self.referenceViewController];

    return cell;
}

So on my understating nothing fancy going on here. I though there was something wrong on the data source (a dummy JSON file), but sometimes it works ok and the cell shows, so I guess from that part is ok.

So my "question": Does anyone knows what's going on? I don't really like to say that it's a bug from iOS, but I can't think of anything else.


Edit 1.0

The amazing part is that this method

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

Is going from indexPath [0,4] to [0,6] without calculating the [0,5]. First time I actually see this happening in iOS.


Edit 2.0

I have switched the way I am creating the cells, and instead of dequeuing I am using the old way:

NSArray *nib = [[NSBundle mainBundle] loadNibNamed:CELL_NIB_NAME owner:self options:nil];
MyCell *cell = (MyCell *)[nib objectAtIndex:0];

Still the same sad result.

9 comments

@fewlinesofcode 2018-10-30 13:08:06

As I run the same problem suddenly and spent some time figuring out one of possible reasons of cell disappearing during the scroll, I will add my answer as well.

Prerequisites of the problem:

  1. You have a UICollectionView instance
  2. You have a UICollectionViewFlowLayoutSubclass

The problem

Cells disappear from the Collection View after scrolling to the certain point.

The source of the problem is in wrong subclassing of the UICollectionViewFlowLayout.

As it explicitly said in documentation:

Every layout object should implement the following methods:

- collectionViewContentSize
- layoutAttributesForElements(in:)
- layoutAttributesForItem(at:)
- layoutAttributesForSupplementaryView(ofKind:at:) // (if your layout supports -supplementary views)
-layoutAttributesForDecorationView(ofKind:at:) // (if your layout supports decoration views)
- shouldInvalidateLayout(forBoundsChange:)

By relying on UICollectionViewFlowLayout implementation of methods above we miss the fact, that func layoutAttributesForElements(in rect: CGRect) and collectionViewContentSize will generate wrong contentSize (the size that would be correct if all the cells would have itemSize size and the content size would be corresponding. As soon as scroll offsetY will be greater that contentSize height cell will all disappear.

The solution

The solution is in proper UICollectionViewFlowLayout subclassing. Override all the methods that are required to override and everything will work just fine.

@tyler 2018-01-08 04:47:09

We ran into disappearing cells recently and found that rather than skipping 'hidden' cells we were accidentally inserting 0x0 sized cells. The resulting behavior was very confusing and did not suggest these invisible cells were the issue. We would see the correctly sized cells and layout, but a few of the valid cells would consistently disappear after scrolling off/on screen. I have no idea why intermingling 0 sized cells would cause this behavior, but removing them fixed the problem. This may not be causing your problem, but this may be helpful to devs searching for similar symptoms.

@lambert.lu 2017-09-08 03:52:52

I think this is not a UICollectionView‘s bug, maybe your not return right data in - (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect method.

You can see this demo: https://github.com/lqcjdx/YLTagsChooser , all cells can appear when scolling the UICollectionView.

@Dbl 2017-08-11 13:21:29

For me this issue seemed to be related with the way i make my collectionview adapt to an open keyboard to prevent content overlaps.

in my observer to respond to KeyboardWillShow i had this:

var userInfo = obj.UserInfo[UIKeyboard.FrameEndUserInfoKey];
if (userInfo is NSValue value)
{
    var rect = value.CGRectValue;
    var windowOffset = this.Superview.ConvertPointToView(this.Frame.Location, UIApplication.SharedApplication.KeyWindow);
    var newHeight = rect.Y - windowOffset.Y;

    this._controller.CollectionView.Frame = new CGRect(0, 0, this._controller.CollectionView.Frame.Width, newHeight);
}

After changing it to this:

var userInfo = obj.UserInfo[UIKeyboard.FrameBeginUserInfoKey];
if (userInfo is NSValue value)
{
    var rect = value.CGRectValue;
    UIEdgeInsets contentInsets = new UIEdgeInsets(0, 0, rect.Height, 0);
    this._controller.CollectionView.ContentInset = contentInsets;
    this._controller.CollectionView.ScrollIndicatorInsets = contentInsets;
}

The cell disappearance issue completely went away. This is C# from working with xamarin but i hope it helps someone else.

@chandan thakur 2016-09-19 04:02:33

In my case (vertical scroll, with cells disappearing in first view), cells were disappearing due to incorrect estimated size. It seems, UICollectionView uses the estimated size to calculate the items to load in first view. I'd set the estimated size too high which was resulting in wrong calculations for number of items to load in first screen.

The moment I made the estimated height bit low, all the cells appeared correctly.

@CoderSaru 2015-11-20 10:53:12

None of the solutions given by anyone helped me in my custom layout that we need to have in our app. Instead, I had to do this: (And yeah, IT WORKS!!!)

- (NSArray *)layoutAttributesForElementsInRect:(CGRect)rect{
    CGSize size = [self collectionViewContentSize];
    rect.size.height = size.height*2;
    NSArray *atrributes_Super = [super layoutAttributesForElementsInRect:rect];
    return atrributes_Super;
}

After all, UICollectionView is just looking for the attributes for the elements to be displayed in your screen's rect.

@jcardenete 2016-05-09 12:50:22

Similar thing happened here. My implementation of layoutAttributesForElementsInRect was not returning the attributes for the desired cell, that in turn was being set as .hidden = YES.

@Yao Li 2015-06-26 18:21:27

The above answers didn't work for me, but after downloading the images, I replaced the code [self.myCollectionView reloadData] with [self.myCollectionView reloadSections:[NSIndexSet indexSetWithIndex:0]]; to refresh the collectionview and it shows all cells, you can try it.

@Jacky Wang 2015-11-25 06:19:34

Wow, this actually worked...

@CIFilter 2017-04-18 21:41:22

Stupidly, this worked for me as well...what's going on with UICollectionView?

@Antoine 2017-05-21 08:27:49

Tried other solutions above, none were working (Swift 3), this one fixed the bug. Strange...

@Itachi Uchiha 2017-11-03 12:56:18

Awesome it works

@Grease 2018-04-19 08:59:36

Can't believe that actually worked, and it added animations for me too.

@Matheus Weber 2019-06-27 14:29:48

Sometimes some random cell disappears too :/

@Rui Peres 2012-11-13 21:02:32

So, what did work?

1) Subclass UICollectionViewFlowLayout.

2) Set the flowLayout of my UICollectionView to my new subclass.

3) On the init method of the UICollectionViewFlowLayout subclass, set the orientation you want:

self.scrollDirection = UICollectionViewScrollDirectionHorizontal;

In my case it is Horizontal.

4) The important part:

-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds
{
   return YES;
}

At this moment, I should theorise a bit, but honestly I don't have a clue.

@rob mayoff 2012-11-13 21:42:56

Take a look at this bug: openradar.appspot.com/12433891 Could it be what you're encountering?

@Rui Peres 2012-11-13 21:48:58

I have to be honest Rob, strange things happen when using UICollectionView, not sure if it's related or not.

@Bryan Luby 2012-11-30 13:19:04

Have you tried fiddling with cell width and height? I'm having the same rendering problem with a horizontally scrolling collection view. I get disappearing cells when my cell width is 70 and height is 70. If I keep the cell width at 70 and change the cell height to 69, it renders correctly. I can reproduce this situation every time.

@Rui Peres 2012-11-30 13:20:30

@BryanLuby after doing what I did in the shouldInvalidateLayoutForBoundsChange:it's working perfectly.

@Michael Luton 2013-01-07 23:17:22

Thanks @rob-mayoff! I was having the same problem. Always random items in the first column disappearing after scrolling down and then up again. Using the one of the subclasses in openradar.appspot.com/12433891 fixed it for me.

@Mark Ingram 2013-02-28 09:25:52

Unfortunately this didn't work for me, but the solution here did -> stackoverflow.com/questions/12927027/… If you output the rects in that function, you'll see it creates two rows / columns so you have to filter it down to 1.

@xaphod 2018-02-05 17:13:57

This solved my crash in layoutSubViews that only occurs in iOS 9 (iOS 10 & 11 are fine), thanks.

@hoak 2013-01-16 03:38:21

Rob's tip about the bug helped me. The bug states that if the section insets and cells widths and spacing add up exactly to the width of the screen then the first column sometimes randomly dissappears and reappears for some cells in some places. Rather than subclass or change the cell widths, I changed the section insets for left and right in my storyboard from 6 to 4 and it I haven't seen the problem again.

@Rui Peres 2013-01-16 07:33:34

I wasn't able to fix it using Rob's solution. But I am really glad it worked for you man.

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