UICollectionView current visible cell index

UICollectionView current visible cell index

I am using UICollectionView first time in my iPad application. I have set
UICollectionView such that its size and cell size is same, means only once
cell is displayed at a time.
Problem: Now when user scroll UICollectionView I need to know which cell
is visible I have to update other UI elements on change. I didn't find any
delegate method for this. How can I achieve this?
Code:
[self.mainImageCollection setTag:MAIN_IMAGE_COLLECTION_VIEW];
[self.mainImageCollection
registerClass:[InspirationMainImageCollectionCell class]
forCellWithReuseIdentifier:@"cellIdentifier"];
[self.mainImageFlowLayout
setScrollDirection:UICollectionViewScrollDirectionHorizontal];
[self.mainImageFlowLayout setMinimumInteritemSpacing:0.0f];
[self.mainImageFlowLayout setMinimumLineSpacing:0.0f];
self.mainImageFlowLayout.minimumLineSpacing = 0;
[self.mainImageCollection setPagingEnabled:YES];
[self.mainImageCollection setShowsHorizontalScrollIndicator:NO];
[self.mainImageCollection setCollectionViewLayout:self.mainImageFlowLayout];
What I have tried:
As UICollectionView Conforms to UIScrollView, I got when user scroll ends
with UIScrollViewDelegate method
-(void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView
But inside above function how can I get current visible cell index of
UICollectionView ???