Changing UITableView section header without tableView:titleForHeaderInSection - ios

Question

I'm trying to change the header title for a section in a UITableView when a cell from that section is selected. tableView:titleForHeaderInSection is triggered by the application, so that doesn't help. I can call reloadData, but the performance suffers because the app has to reload all the visible cells. I also tried to use a custom header, but that also results in some performance problems.
Is there any way to get a handle to the UILabel that the default header view uses and change its text manually?

Answer 1

Calling [tableView endUpdates] may provide the desired results without too much of a performance hit.
[self.tableView beginUpdates];
[self.tableView endUpdates];
// forces the tableView to ask its delegate/datasource the following:
// numberOfSectionsInTableView:
// tableView:titleForHeaderInSection:
// tableView:titleForFooterInSection:
// tableView:viewForHeaderInSection:
// tableView:viewForFooterInSection:
// tableView:heightForHeaderInSection:
// tableView:heightForFooterInSection:
// tableView:numberOfRowsInSection:

Answer 2

with:
[self.tableView headerViewForSection:i]
you could get the view for Section i and then "update" it manually
this even works if your view is just the auto-generated label, but you will have to resize it yourself.
so if you try to:
[self.tableView headerViewForSection:i].textLabel.text = [self tableView:self.tableView titleForHeaderInSection:i];
you will set the text, but you would not set the label-size. You can get the needed size from NSString to set it yourself:
[label.text sizeWithFont:label.font];

Answer 3

There doesn't appear to be any standard API for accessing the system-provided section header view. Have you tried the more targeted reloadSections:withRowAnimation to get UIKit to display the new header text?
What kind of performance issues were you seeing with custom section header views? I doubt that the standard one is much more than just a UILabel.

Answer 4

You can set the title for the section header label directly. For example, to set the title of section zero:
UITableViewHeaderFooterView *sectionZeroHeader = [self.tableView headerViewForSection:0];
NSString *sectionZeroLabel = #"Section Zero";
[sectionZeroHeader.textLabel setText:[sectionZeroLabel uppercaseString]];
[sectionZeroHeader setNeedsLayout];
Be sure and tell the section header view it needs layout, otherwise the new text may be truncated. Also, section labels are usually all uppercase.

Answer 5

Since a UITableView does not enqueue and dequeue section header views for reuse, you might as well see if it's feasible to store all the section header views in memory. Note you'll have to create your own section header views with the background and etc., to do this, but it allows you a bit more flexibility and capability.
You could also try tagging the section header views (also requires you to create your own section header views) and just grab them from the tableview as needed.

Answer 6

This is a WAG, and I can think of lots of reasons why it might not work, but couldn't you iterate through the subviews, and find the one you are looking for? E.g.
for (UIView *v in self.tableView.subviews) {
// ... is this the one?
}

Answer 7

One of the solution would be to manage external array for multiple section headers containing label references and update them externally.

Answer 8

For completeness, the method we are all looking for is this private API named exactly what you'd expect:
-(void)_reloadSectionHeaderFooters:withRowAnimation:
eg:
[tableView _reloadSectionHeaderFooters:[NSIndexSet indexSetWithIndex:indexPath.section] withRowAnimation:UITableViewRowAnimationAutomatic]
I do not recommend using this, however.

Answer 9

If you want to update only one section best way is tableView.headerView. If header is not visible it returns nil, so it doesn't load extra headers.
if let header = tableView.headerView(forSection: i) {
header.textLabel!.text = "new title"
header.setNeedLayout()
}
If you want to update all visible section headers it is better to set header tag as section before view is displayed and enumerate subviews when needed:
func tableView(_ tableView: UITableView, willDisplayHeaderView view: UIView, forSection section: Int) {
view.tag = section
// additional customization
}
func udpateVisibleSectionHeaders() {
for subview in tableView.subviews {
if let header = subview as? UITableViewHeaderFooterView {
let section = header.tag
header.textLabel!.text = "new title"
header.setNeedsLayout()
}
}
}
Don't forget to call setNeedsLayout or label can be truncated.