Make UICollectionViewFlowLayout handle page sizes that are less than the width. #ios #UICollectionView #scrolling #carousel

UICollectionViewFlowLayoutCenterItem.m

- (CGPoint)targetContentOffsetForProposedContentOffset:(CGPoint)proposedContentOffset withScrollingVelocity:(CGPoint)velocity
{
    // We're going to center the centermost item...
    
    // Use the bounds to have the snap happen the minute drag stops. In other words use the current content offset (which = bounds.origin) instead of the proposed end offset (which takes velocity into account)
    CGRect proposedRect = self.collectionView.bounds;
    
    CGFloat proposedContentOffsetCenterX = proposedContentOffset.x + self.collectionView.bounds.size.width * 0.5f;
    
    // Comment out if you want the collectionview simply stop at the center of an item while scrolling freely (ie take velocity into account)
//    CGSize collectionViewSize = self.collectionView.bounds.size;
//    proposedRect = CGRectMake(proposedContentOffset.x, 0.0, collectionViewSize.width, collectionViewSize.height);
    
    // Find the attribute/cell, in the relevant visible rect which is closest to the proposed offeset.  Why proposed?  B/c this is a clever trick to ensure we round to the cell towards the direction of the scroll.
    UICollectionViewLayoutAttributes* candidateAttributes;
    // Find the attribute/cell which is
    for (UICollectionViewLayoutAttributes* attributes in [self layoutAttributesForElementsInRect:proposedRect])
    {
        
        // == Skip comparison with non-cell items (headers and footers) == //
        if (attributes.representedElementCategory != UICollectionElementCategoryCell)
        {
            continue;
        }
        
        // == First time in the loop == //
        if(!candidateAttributes)
        {
            candidateAttributes = attributes;
            continue;
        }
        
        if (fabsf(attributes.center.x - proposedContentOffsetCenterX) < fabsf(candidateAttributes.center.x - proposedContentOffsetCenterX))
        {
            candidateAttributes = attributes;
        }
    }
    
    return CGPointMake(candidateAttributes.center.x - self.collectionView.bounds.size.width * 0.5f, proposedContentOffset.y);
}