How to scroll UICollectionViewCell programmatically in IOS?

Question

I have a vertical UICollectionView with each cell taking up the entire self.view.frame I can easily swipe upwards to page to the next cell, but I would like to do the same thing with the press of a button.

I've tried using:

- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated

And:

- (void)scrollRectToVisible:(CGRect)rect animated:(BOOL)animated

They work but they temporarily "White-Out" the currentCell to present the nextCell, while the swiping shows both cells during the transition.

Ideally I would like to use:

- (void)scrollToItemAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UICollectionViewScrollPosition)scrollPosition animated:(BOOL)animated

But I don't know how to access the nextCell's indexPath... I've tried:

NSIndexPath *nextIndexPath = [_collectionView indexPathForItemAtPoint:CGPointMake(25, (_collectionView.frame.size.height-25)*(_currentIndexRowForCellOnScreen+1))];

Where _currentIndexRowForCellOnScreen is the indexPath.row of the UICollectionView's first appearance on screen in:

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

But when I put it into:

- (NSIndexPath *)indexPathForCell:(UICollectionViewCell *)cell

it returns NULL after the first Cell, and does not animate....

Any direction would be greatly appreciated. Thank you for your time.

Answer 1

Assuming your collectionView contains only 1 section, and given that each item occupies the whole frame then you could do something like this;

  NSArray *visibleItems = [self.collectionView indexPathsForVisibleItems];
  NSIndexPath *currentItem = [visibleItems objectAtIndex:0];
  NSIndexPath *nextItem = [NSIndexPath indexPathForItem:currentItem.item + 1 inSection:currentItem.section];
  [self.collectionView scrollToItemAtIndexPath:nextItem atScrollPosition:UICollectionViewScrollPositionTop animated:YES];