Assertion Failure in UICollectionViewData validate

Question

Assertion Failure in UICollectionViewData validateLayoutInRect on iOS7.

I am trying to delete all UICollectionView items, one by one, using a for loop; I posted my code below. I delete the UICollectionView items using deleteItemsAtIndexPaths. It's working perfectly on iOS6, but crashes in iOS7 with this exception:

Assertion Failure in UICollectionViewData validateLayoutInRect

I delete the object from collectionArray then self.collectionView, one by one, using indexPath. When I delete the 4th object its raises Assertion failure on iOS7. Here I am using performBatchUpdates.

Please help me get the proper result in iOS7. Share proper code. Thanks in advance.

try  {    
    for (int i=count-1; i>=0; i--)  {  
        [self.collectionView performBatchUpdates:^(void){  
            [collectionArray removeObjectAtIndex:i]; // First delete the item from you model   
            [self.collectionView deleteItemsAtIndexPaths:@[[NSIndexPath indexPathForRow:i inSection:0]]];  
        } completion:nil];
        [self.collectionView reloadData];
    }
}
@catch (NSException *exception) {
}
@finally {
}

Answer 1

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    [collectionView.collectionViewLayout invalidateLayout];
    return 1;
}

Answer 2

In my case following delegate was missing:

func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

Answer 3

You should implement invalidateLayout in your layoutClass and remove all kinds of UICollectionViewLayoutAttributes items in your config.

- (void)invalidateLayout{
  [super invalidateLayout];
  [self.itemsAttributes removeAllObjects];
}

Answer 4

try to call [yourCollectionView.collectionViewLayout invalidateLayout];

Answer 5

It looks like you probably want to do this:

[self.CollectionView performBatchUpdates:^(void) {
  for (int i = count - 1; i >= 0; i--) {
    [collectionArray removeObjectAtIndex:i]; // First delete the item from you model
    [self.CollectionView deleteItemsAtIndexPaths:@[[NSIndexPath indexPathForRow:i inSection:0]]];
  }
} completion:nil];

So that all the updates are performed together. Otherwise you will end up trying to perform several lots of batch updates on top of each other.

Answer 6

I actually got this crash one time not because I was returning zero for a number of sections or items in a section but because I was reusing a flow layout like this for more than 1 collection view:

UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
Collection1 = [[UICollectionView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 50.0f) collectionViewLayout:flowLayout];
[Collection1 setDataSource:self];
[Collection1 setDelegate:self];
[self.view addSubview:Collection1];

Collection2 = [[UICollectionView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, self.view.frame.size.height) collectionViewLayout:flowLayout];
Collection2.backgroundColor = [UIColor whiteColor];

Instead if I create a new flow layout for each UICollectionView I avoid this crash. Hopefully that might help someone

UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionHorizontal];
Collection1 = [[UICollectionView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 50.0f) collectionViewLayout:flowLayout];
[Collection1 setDataSource:self];
[Collection1 setDelegate:self];
[self.view Collection1];

UICollectionViewFlowLayout *flowLayoutVert = [[UICollectionViewFlowLayout alloc] init];
[flowLayoutVert setScrollDirection:UICollectionViewScrollDirectionVertical];
Collection2 = [[UICollectionView alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, self.view.frame.size.height) collectionViewLayout:flowLayoutVert];