UITableView: delete not visible rows - ios

Question

My question is about deleting "invisible" rows in a UITableView. When I say invisible, I mean rows that are not showed on the screen. For example, all the rows that aren't returned by calling the UITableView method - (NSArray *)visibleCells.
I'm asking this because I'm developping an "expandable" UITableView. A little bit like a tree. You can have a table like this :
Menu 1
Menu 1.1
Menu 1.2
Menu 2
Menu 2.1
Menu 2.2
And when you click on "Menu 1" the cells "Menu 1.1" and "Menu 1.2" will either appear or disappear. I do this by simply inserting or deleting cells with an animation.
The problem is, if I have long menus and the user scrolls, if half the rows from "Menu 1", for instance, ar hidden (not visible, not showed on the screen, visible only if you scroll down) and that the user wants to reduce "Menu 1" this will cause my application to crash because I'm trying to delete rows that are not visible.
The actual error message is :
* Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid
number of rows in section 0. The number of rows contained in an
existing section after the update (11) must be equal to the number of
rows contained in that section before the update (15), plus or minus
the number of rows inserted or deleted from that section (0 inserted,
0 deleted) and plus or minus the number of rows moved into or out of
that section (0 moved in, 0 moved out).'
If I do the exact same manipulation with all the rows visible, no problem with the app and the menu behaves correctly.

Answer 1

On your tableview update calls, you need to update the tableview data source as well as the tableview. You can use UITableView's indexPathsForVisibleRows method to find the positions in which to remove the objects from the source, and update your table.

Answer 2

Thanks to all of you for your answers. What I did is I used "indexPathsForVisibleRows" to get the indexPaths of the rows not displayed on the screen and I simply updated my model and called "reloadData" to update my table. This is not the ideal solution I was expecting but it works.
I still don't understand why "-deleteRowsAtIndexPaths" doesn't work for rows not on the screen but actually really present in the table.

Answer 3

I had a similar problem and here goes my solution. Basically the solution involves on changing the cells height to "hide" them.
I've changed the section header to a custom UIControl to looks like any other cell and implemented the follow method to "hide" the rows outside the selected section:
- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.section == _selectedSection) {
// If it is the selected section then the cells are "open"
return 60.0;
} else {
// If is not the selected section then "close" the cells
return 0.0;
}
}
For the custom header I've used the following code:
- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
CGFloat height = [self tableView:tableView heightForHeaderInSection:section];
// Here you can use whatever you want
CGFloat width = 640.0;
UIControl *view = [[UIControl alloc] initWithFrame:CGRectMake(0.0, 0.0, width, height)];
view.tag = section;
// This code is used by my custom UIControl
//
// to change the style for each state
// view.sectionSelected = (section == _selectedSection);
//
// and to change the title
// view.title = [self tableView:tableView titleForHeaderInSection:section];
// This event is used to "close" or "open" the sections
[view addTarget:self action:#selector(didSelectSectionHeader:) forControlEvents:UIControlEventTouchUpInside];
return view;
}
To be more appealing I've added animations to the following method:
- (void)didSelectSectionHeader:(id)sender
{
if ([sender isKindOfClass:[UIControl class]]) {
// Save the old section index
int oldSelection = _selectedSection;
// Get the new section index
int tag = ((UIControl *)sender).tag;
// Get sections quantity
int numSections = [self numberOfSectionsInTableView:_tableView];
// Check if the user is closing the selected section
if (tag == _selectedSection) {
_selectedSection = -1;
} else {
_selectedSection = tag;
}
// Begin animations
[_tableView beginUpdates];
// Open the new selected section
if (_selectedSection >= 0 && _selectedSection < numSections) {
[_tableView reloadSections:[NSIndexSet indexSetWithIndex:_selectedSection] withRowAnimation:UITableViewRowAnimationAutomatic];
}
// Close the old selected section
if (oldSelection >= 0 && oldSelection < numSections) {
[_tableView reloadSections:[NSIndexSet indexSetWithIndex:oldSelection] withRowAnimation:UITableViewRowAnimationAutomatic];
}
[_tableView endUpdates];
}
}