UICollectionView find center cell when content inset is used - ios

Question

I'm trying to figure out how to find the center most cell of my UICollectionView, which is set to only scroll horizontally.
I tried this SO: how to get indexPath for cell which is located in the center of UICollectionView but it isn't working out, I think because I'm using the contentInset property of my UICollectionView.
What I'm doing is setting the contentInset left and right of the flow layout to exactly 1/2 of self.view's bounds width minus 1/2 of itemSize width. I'm not sure how to calculate the center most cell due to this. I'd appreciate any help offered. Code:
CGPoint cellCenter = CGPointMake((self.collectionView.center.x +
self.collectionView.contentOffset.x) -
(self.sampleFlowLayout.sectionInset.left +
self.sampleFlowLayout.sectionInset.right), self.collectionView.center.y);
NSIndexPath *indexPath = [self.collectionView indexPathForItemAtPoint:cellCenter];
if (indexPath)
{
NSInteger tag = [self.collectionView cellForItemAtIndexPath:indexPath].tag;
if (tag != self.currentSample)
{
self.currentSample = tag;
self.imageView.image = [self sampleImageWithOption:self.currentSample];
}
}
- (void)viewDidLoad
{
self.sampleFlowLayout = [[UICollectionViewFlowLayout alloc]init];
CGSize itemSize = CGSizeMake(63, 63);
self.sampleFlowLayout.scrollDirection = UICollectionViewScrollDirectionHorizontal;
self.sampleFlowLayout.sectionInset = UIEdgeInsetsMake(0, (self.view.bounds.size.width / 2) - (itemSize.width / 2), 0, (self.view.bounds.size.width / 2) - (itemSize.width / 2));
}

Answer 1

I figured this out myself using help from this answer: https://stackoverflow.com/a/22696037/1533438
Final code:
- (void)snapCollectionView:(UICollectionView *)collectionView withProposedOffset:(CGPoint)proposedOffset
{
CGRect cvBounds = collectionView.bounds;
CGFloat halfWidth = cvBounds.size.width * 0.5;
CGFloat proposedContentOffsetCenterX = proposedOffset.x + halfWidth;
NSArray *attributesArray = [collectionView.collectionViewLayout layoutAttributesForElementsInRect:cvBounds];
UICollectionViewLayoutAttributes *candidateAttributes;
for (UICollectionViewLayoutAttributes *attributes in attributesArray)
{
if (attributes.representedElementCategory !=
UICollectionElementCategoryCell)
{
continue;
}
if (!candidateAttributes)
{
candidateAttributes = attributes;
continue;
}
if (fabsf(attributes.center.x - proposedContentOffsetCenterX) <
fabsf(candidateAttributes.center.x - proposedContentOffsetCenterX))
{
candidateAttributes = attributes;
}
}
CGPoint offset = CGPointMake(candidateAttributes.center.x - halfWidth, proposedOffset.y);
[collectionView setContentOffset:offset animated:YES];
CGPoint cellCenter = CGPointMake(offset.x + self.sampleCollectionView.bounds.size.width / 2.0, self.sampleCollectionView.bounds.size.height / 2.0);
NSIndexPath *indexPath = [self.sampleCollectionView indexPathForItemAtPoint:cellCenter];
if (indexPath)
{
NSInteger tag = [self.sampleCollectionView cellForItemAtIndexPath:indexPath].tag;
if (tag != self.currentSample)
{
self.currentSample = tag;
UIImage *image;
if (self.currentSample == 0)
{
image = self.image;
}
else
{
image = [self sampleImageWithOption:self.currentSample];
}
dispatch_async(dispatch_get_main_queue(),
^{
self.imageView.image = image;
});
}
}
}