Cell disappears after reloading when using estimatedSize - ios

Question

I'm having a weird issue, when using a collection view with dynamic sizes, this issue doesn't happens while using fixed sizes.
After a reload the first cell of each section disappears, but only if they are out of the screen. After a few tests I realize that the cell didn't disappear, but its hidden bellow the section header.
Do you have any idea what is causing this?
Collection without reloading:
Collection after reloading with cell visible:
Collection after reloading with cell out of screen:
3D view of the cell after reloading:
The code:
#pragma mark - UICollectionViewDataSource
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
return self.sections.count;
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)sectionIndex {
Section *section = [self.sections objectAtIndex:sectionIndex];
return section.items.count;
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
Section *section = [self.sections objectAtIndex:indexPath.section];
Item *item = [section.items objectAtIndex:indexPath.row];
if (self.editing) {
EditingCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"cell-editing" forIndexPath:indexPath];
cell.item = item;
return cell;
} else {
BasicCollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:#"cell" forIndexPath:indexPath];
cell.item = item;
return cell;
}
}
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath {
if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
HeaderCollectionReusableView *header = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:#"header" forIndexPath:indexPath];
Section *section = [self.sections objectAtIndex:indexPath.section];
header.title = section.title;
return header;
} else {
UICollectionReusableView *footer = [collectionView dequeueReusableSupplementaryViewOfKind:kind withReuseIdentifier:#"footer" forIndexPath:indexPath];
return footer;
}
}
#implementation DetailCollectionViewLayout
- (instancetype)init {
if (self = [super init]) {
[self initialize];
}
return self;
}
- (instancetype)initWithCoder:(NSCoder *)aDecoder {
if (self = [super initWithCoder:aDecoder]) {
[self initialize];
}
return self;
}
- (void)prepareLayout {
CGFloat cellWidth = (isIPAD) ? 288 : CGRectGetWidth(self.collectionView.bounds);
CGFloat headerWidth = CGRectGetWidth(self.collectionView.bounds);
// CGFloat ratio = (isIPAD) ? 0.33 : 0.66;
self.estimatedItemSize = CGSizeMake(cellWidth, 53);
self.headerReferenceSize = CGSizeMake(headerWidth, 50);
self.footerReferenceSize = CGSizeMake(headerWidth, 1 + self.minimumInteritemSpacing);
[super prepareLayout];
}
- (void)initialize {
self.minimumLineSpacing = 0;
self.minimumInteritemSpacing = (isIPAD) ? 5 : 10;
self.estimatedItemSize = CGSizeZero;
self.scrollDirection = UICollectionViewScrollDirectionVertical;
self.sectionInset = UIEdgeInsetsZero;
}
-(BOOL)shouldInvalidateLayoutForBoundsChange:(CGRect)newBounds {
return YES;
}
#end
I made a simple sample project and record a video: http://sendvid.com/330uo5jm
It looks like the issue is the position from the first cell.

Answer 1

UICollectionViewCell autosizing can be a little, uh... interesting even at the best of times. I've had this exact issue in the past, and similar issues too.
Use a different value for .estimatedItemSize, the closer to the actual item size the better. I noticed you're using a size of CGRectZero at first. I wouldn't recommend doing that. Just set it once, at the start, with a value close to your size. Try a few values, see what works for you. For me, it took a bit of fine tuning.
For anyone developing for iOS 10 (at the time of writing this hasn't been released) there is a new collection view property that lets the collection view determine the estimated size itself. Set the itemSize to UICollectionViewFlowLayoutAutomaticSize, you shouldn't need to set .estimatedItemSize explicitly.

Answer 2

make sure your estimatedItemSize in your code same as size of cell in your xib or storyboard.Don't changes it's size runtime.
can you check with use of identifier like...
NSString *CellIdentifier = [NSString stringWithFormat:#"%d_%d",indexPath.section,indexPath.row];

Answer 3

Sometimes it happens if you have a big difference between estimated size and real size of cell.
Check you have a clear consequence of top to bottom constraints (if you are using autolayout).
Is there something that can break the autolayout to work properly ? E.g compresion resistance settings ?
Are you sure there are data for the cell after reload ? (Will be weird, but to be sure, just double check that.)
Also as Apple denotes here Apple - self sizing guide try to set the estimation of size as close as possible to real dimensions.
You can also try to refer to invalidation of collection layout as you are using your own. Refer to Possible flow-layout help
Try to set the estimation as close as possible and you will see if it solve your problem.