GettingStartedWithCustomUICollectionViewLayouts-4

CustomLayout.m

-(UICollectionViewLayoutAttributes *)layoutAttributesForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewLayoutAttributes* attr = [UICollectionViewLayoutAttributes layoutAttributesForCellWithIndexPath:indexPath];
 
    CGRect cellFrame = CGRectMake(/* calculate your origin x */,
                                  /* calculate your origin y */,
                                  /* calculate your width */,
                                  /* calculate your height */);
    attr.frame = cellFrame;
 
    return attr;
}