UiTableView header not disappearing - ios

Question

I have a UITableView configured as plain style so I can have the header views stuck on the top of the table until another header pulls it away.
The problem is: If I have a header stuck on the top of the screen, and I programmatically scroll to another part of the table (where that header should not appear at all), that UIView will not be dismissed. I.e. if I scroll again to that part of the table, a ghost of that header will be visible on that part of the table.
I've implemented the method - (void)tableView:(UITableView *)tableView didEndDisplayingHeaderView:(nonnull UIView *)view forSection:(NSInteger)section to understand what is happening. I found that if I manually scroll until a header is pull away of the screen, this delegate is called. But if I scroll programmatically, the delegate is not called.
By the way, I tried scrolling programmatically using two different methods, and the problem is the same.
- (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated;
- (void)scrollToRowAtIndexPath:(NSIndexPath *)indexPath atScrollPosition:(UITableViewScrollPosition)scrollPosition animated:(BOOL)animated;
One workaround that I can imagine is implementing - (void)scrollViewDidScroll:(UIScrollView *)scrollView;, filtering all the header views that are outside the visible screen, and removing them from superview. I can probably make it work, but I would like to know if there is any other better solution.
[EDIT] If I call - (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated; with animated = YES, the bug does not happen. I can go with this solution, but I really would like in some cases to scroll without animation.

Answer 1

Not entirely sure I understand your issue entirely but it seems that your header view(s) (some UIView) is/are not rendered correctly once you programmatically scroll away from this area / section and then return.
I'm not sure how you are filling your header view content but I have several applications running UITableView's with multiple section headers that require updating for scrolling / content offset's with no problem, as long as you "draw" your headers with this delegate:
- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section {
// Per section, simply return the appropriate header view
...
NSString *someIdentifier = [NSString stringWithFormat:#"sectionHeaderView:<some #, letter, or tag>", <SOMETHING UNIQUE ADD HERE>];
UITableViewHeaderFooterView *myHeaderView = [self.tableView dequeueReusableHeaderFooterViewWithIdentifier:someIdentifier];
if (!myHeaderView) {
// No header view found with that ID. Make a new one
}
...
return myHeaderViewForSection;
}
This way whether you finger scroll or programmatically set the content offset which ever way you like, your table view will know what to draw, when to draw it, and where to put it.
Using their delegates is a bit of a drag as it's slightly tedious at start, but using the viewForHeaderInSection proved the only way I ever obtained the results I (you) wanted.
Hope this helps - happy coding!

Answer 2

TL;DR
Do NOT explicitly scroll the table view between beginUpdates and endUpdates.
Explanation
I'm using NSFetchedResultsController to populate the table. These are my implementations for some of the methods of NSFetchedResultsControllerDelegate.
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
[_conversationTableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
[_conversationTableView endUpdates];
}
The problem is that endUpdates was making a chain of calls that ended calling my method [self scrollToBottom] (which was a very ugly code actually). This method, as the name says, calls - (void)setContentOffset:(CGPoint)contentOffset animated:(BOOL)animated; to scroll the table view to the bottom of the table.
The explicit scrolling of the table during a beginUpdates - endUpdates was the culprit of my whole problem.
Solution
Scrolling the table view only after finishing endUpdates.
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
[_conversationTableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
[_conversationTableView endUpdates];
[self scrollToBottom];
}
Side Note
This also fixed a problem where the table view was sometimes flickering when scrolling.

Answer 3

Manually set the sectionHeader height to 0 when it should not appear
tableView.sectionHeaderHeight = 0;