collectionView

/// 这里是水平滚动的colletionView ,所以 使用了x
- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    if (scrollView == self.collectionView ) {
        if (!(scrollView.isTracking || scrollView.isDecelerating) || scrollView != self.collectionView) {
            //不是用户滚动的，比如setContentOffset等方法，引起的滚动不需要处理。
            return;
        }
        //用户滚动的才处理
        NSInteger index=scrollView.contentOffset.y;
        CGRect visibleRect = (CGRect){.origin = scrollView.contentOffset, .size = scrollView.bounds.size};
        UICollectionViewLayoutAttributes *topAttributes = [self.collectionView.collectionViewLayout layoutAttributesForElementsInRect:visibleRect].firstObject;
        NSLog(@"visibleIndexPath  =  %ld",index);
        NSLog(@"topAttributes.section  =  %ld",topAttributes.indexPath.section);
    }
}

//调用此方法可滚动到组头 collectionView
-(void) scrollToSectionHeaderWithCollectionView:(UICollectionView *)collectionView section:(NSInteger)section {
    NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:section];
    UICollectionViewLayoutAttributes *attribs =
    [collectionView layoutAttributesForSupplementaryElementOfKind:UICollectionElementKindSectionHeader atIndexPath:indexPath];
    CGPoint topOfHeader = CGPointMake(0, attribs.frame.origin.y - collectionView.contentInset.top);
    [collectionView setContentOffset:topOfHeader animated:YES];
}