Rows not being inserted into UITable - ios

Question

I have an app with a table view that expands/collapses sections, following the example in Apple's Table View Animations & Gestures sample app. I am running into problems when an item is added to a closed section: after that, the section no longer opens, and I get an exception when I try to open and then close it.
I've traced this to some strange behaviour in the open/close methods:
-(void)sectionHeaderView:(SectionHeaderView*)sectionHeaderView sectionOpened:(NSInteger)section {
if (![[sectionHeaderArray objectAtIndex:section] isOpen]) {
[[sectionHeaderArray objectAtIndex:section] setIsOpen:YES];
NSLog(#"self.tableView: %#", self.tableView);
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section];
NSInteger countOfRowsToInsert = [sectionInfo numberOfObjects];
NSMutableArray *indexPathsToInsert = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < countOfRowsToInsert; i++) {
[indexPathsToInsert addObject:[NSIndexPath indexPathForRow:i inSection:section]];
}
// Apply the updates.
[self.tableView beginUpdates];
NSLog(#"Count of rows to insert: %d", [indexPathsToInsert count]);
NSLog(#"Rows before insert: %d", [self.tableView numberOfRowsInSection:section]);
[self.tableView insertRowsAtIndexPaths:indexPathsToInsert withRowAnimation:UITableViewRowAnimationTop];
NSLog(#"Rows after insert: %d", [self.tableView numberOfRowsInSection:section]);
[self.tableView endUpdates];
}
}
-(void)sectionHeaderView:(SectionHeaderView*)sectionHeaderView sectionClosed:(NSInteger)section {
if ([[sectionHeaderArray objectAtIndex:section] isOpen]) {
[[sectionHeaderArray objectAtIndex:section] setIsOpen:NO];
NSInteger countOfRowsToDelete = [self.tableView numberOfRowsInSection:section];
if (countOfRowsToDelete > 0) {
NSMutableArray *indexPathsToDelete = [[NSMutableArray alloc] init];
for (NSInteger i = 0; i < countOfRowsToDelete; i++) {
[indexPathsToDelete addObject:[NSIndexPath indexPathForRow:i inSection:section]];
}
[self.tableView beginUpdates];
NSLog(#"Count of rows to delete: %d", [indexPathsToDelete count]);
NSLog(#"Rows before delete: %d", [self.tableView numberOfRowsInSection:section]);
[self.tableView deleteRowsAtIndexPaths:indexPathsToDelete withRowAnimation:UITableViewRowAnimationTop];
NSLog(#"Rows after delete: %d", [self.tableView numberOfRowsInSection:section]);
}
[self.tableView endUpdates];
}
}
The log messages show that, on open (insert rows), >0 rows are being inserted, and yet the row count for that section stays 0:
2012-03-31 13:36:17.454 QuickList7[5523:fb03] Count of rows to insert: 3
2012-03-31 13:36:17.454 QuickList7[5523:fb03] Rows before insert: 0
2012-03-31 13:36:17.454 QuickList7[5523:fb03] Rows after insert: 0
This sets up an inconsistent state between the table and data source, and then when I try to "collapse" the section, I get the following exception:
2012-03-31 13:48:35.783 QuickList7[5523:fb03] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid table view update. The application has requested an update to the table view that is inconsistent with the state provided by the data source.'
How can I insert 3 rows, and still end up with 0 rows?
Thanks,
Sasha

Answer 1

I found the problem! It was actually in the fetchedResultsController's change handler. It was responding to changes to closed sections, which left the table in a bad state, and out of sync with the data source. So I added a check for each update to only insert/delete/update rows if the containing section is open.
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
UITableView *tv = self.tView;
switch(type) {
case NSFetchedResultsChangeInsert:
if ([[sectionHeaderArray objectAtIndex:newIndexPath.section] isOpen]) {
[tv insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
}
break;
case NSFetchedResultsChangeDelete:
if ([[sectionHeaderArray objectAtIndex:indexPath.section] isOpen]) {
[tv deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
break;
case NSFetchedResultsChangeUpdate:
if ([[sectionHeaderArray objectAtIndex:indexPath.section] isOpen]) {
[self configureCell:[tv cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
}
break;
case NSFetchedResultsChangeMove:
if ([[sectionHeaderArray objectAtIndex:indexPath.section] isOpen]) {
[tv deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
}
if ([[sectionHeaderArray objectAtIndex:newIndexPath.section] isOpen]) {
[tv insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
}
break;
}
}

Answer 2

In my app I've implemented a similar behavior in a very different way because I was running into this type of problem a lot.
I have a table with MenuNameCells, MenuItemCells and a static cell at the bottom. Only one menu is expanded at a time, and tapping a MenuNameCell expands or collapses that menu. Since I keep the MenuNameCell in its own section and the MenuItemCells in another, I only have to insert/delete entire sections when I reload the table.
Here's my table's data source:
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
// number of menus, plus 1 if a menu is open, plus 1 static cell
return [self.restaurant.menus count]+(self.menu != nil ? 1 : 0)+1;
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
// if this section is our selected menu, return number of items, otherwise return 1
int numberOfRowsInSection = ([self indexPathIsInMenuItemSection:section] ? [[self.menu items] count] : 1);
return numberOfRowsInSection;
}
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
if (indexPath.section == [tableView numberOfSections]-1) {
// ... set up and return static cell
}
if ([self indexPathIsInMenuItemSection:indexPath.section]) {
// ... set up and return menu item cell
} else {
// ... set up and return menu name cell
}
}
and my table's delegate:
- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
[tableView deselectRowAtIndexPath:indexPath animated:YES];
// return if it's a static cell
if (indexPath.section==[tableView numberOfSections]-1)
return;
// if it's a menu name cell, close open menu and maybe expand this menu
if (![self indexPathIsInMenuItemSection:indexPath.section]) {
BOOL reset = self.menu == m;
if (reset) [self reloadTableView:self.tableView withMenu:nil animated:YES autoscroll:NO];
else [self reloadTableView:self.tableView withMenu:m animated:YES autoscroll:YES];
}
}
There were a couple of helpers mentioned in there:
- (BOOL)indexPathIsInMenuItemSection:(NSInteger)section
{
// returns YES if section refers to our MenuItemCells
int indexOfMenu = [self.restaurant getIndexOfMenu:self.menu];
return indexOfMenu != -1 && section == indexOfMenu+1;
}
- (void)reloadTableView:(UITableView *)tableView withMenu:(Menu *)menu animated:(BOOL)animated autoscroll:(BOOL)autoscroll
{
int oldIndex = [self.restaurant getIndexOfMenu:self.menu];
int newIndex = [self.restaurant getIndexOfMenu:menu];
[tableView beginUpdates];
if (oldIndex != -1) {
// index of [section for items] is oldIndex+1
[tableView deleteSections:[NSIndexSet indexSetWithIndex:oldIndex+1] withRowAnimation:UITableViewRowAnimationTop];
}
if (newIndex != -1) {
// index for [section for items] is newIndex+1
[tableView insertSections:[NSIndexSet indexSetWithIndex:newIndex+1] withRowAnimation:UITableViewRowAnimationTop];
[self setMenu:menu];
} else {
// no new menu
[self setMenu:nil];
}
[tableView endUpdates];
if (autoscroll) [self autoscroll];
}
- (void)autoscroll
{
if (self.menu != nil) {
int section = [self.restaurant getIndexOfMenu:self.menu];
if (section != -1) {
NSUInteger indexes[] = {section,0};
NSIndexPath *indexPath = [NSIndexPath indexPathWithIndexes:indexes length:2];
[self.tableView scrollToRowAtIndexPath:indexPath atScrollPosition:UITableViewScrollPositionTop animated:YES];
}
}
}
Since my data is loaded asynchronously elsewhere, I have this controller set up to receive an NSNotification, but it should work just as well to call this on viewDidAppear:
[self reloadTableView:self.tableView withMenu:self.menu animated:YES autoscroll:YES];
I hope this helps! Let me know if I can clarify any of it.