Question

When I add some hidden header view, like search bar, to the table view, it scrolls automatically to content’s top or table cell’s top, when I set the offset of the scroll to the middle of a search bar. (I used below code)

// in viewDidLoad section
UISearchBar *searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(0, 0, 320, 44)]
[self.tableView setTableHeaderView:searchBar]

// in viewWillAppear: section
[self.tableView setContentOffset:CGPointMake(0, 44)];

For example, if I scroll up a little amount when the search bar is hidden, it automatically scrolls to display the entire search bar.
And if I scroll down a little when the search bar is displayed, it automatically scrolls to make the search bar hidden.

I used below code to implement this feature to my collection view’s header, but that wasn’t exactly the same as the table view’s feature.

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
    CGFloat offset = scrollView.contentOffset.y;
    if (offset > 22 && offset < 44) {
        [scrollView setContentOffset:CGPointMake(0, 44) animated:YES];
    } else if (offset > 44) {
        return;
    } else {
        [scrollView setContentOffset:CGPointMake(0, 0) animated:YES];
    }
}

I think it is very hard to mimic above feature exactly, because the judgment of displaying the entire search bar or hiding the search bar is very subtle.

So my question is, “Is there any pre-implemented method in iOS SDK, or in UICollectionViewController?”.

I googled for many hours but I couldn’t found the answer.

Answer 1

I couldn’t find the pre-implemented way to implement that feature, but the below way seems to make things similar to that of table view’s.

First, add CGFloat type ivar originScrollOffset.

Then, I used the below code to implement scroll view delegate.

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    originScrollOffset = scrollView.contentOffset.y;
}

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
    CGFloat endScrollOffset = scrollView.contentOffset.y;
    NSLog(@"%f %f", originScrollOffset, endScrollOffset);
    if (endScrollOffset <= 44 && endScrollOffset >= 0) {
        if (originScrollOffset >= 44) {
            if (originScrollOffset - endScrollOffset > 10) {
                originScrollOffset = 0;
                [self.collectionView setContentOffset:CGPointMake(0, 0) animated:YES];
            } else {
                originScrollOffset = 44;
                [self.collectionView setContentOffset:CGPointMake(0, 44) animated:YES];
            }
        } else {
            if (endScrollOffset - originScrollOffset > 10) {
                originScrollOffset = 44;
                [self.collectionView setContentOffset:CGPointMake(0, 44) animated:YES];
            } else {
                originScrollOffset = 0;
                [self.collectionView setContentOffset:CGPointMake(0, 0) animated:YES];
            }
        }
    }
}