Why can't I remove the bottom row of my UITableView?

Question

When the user clicks Edit, my UITableView adds the insert line at the top (with a green plus) and puts all the other rows in delete mode (red minus). Alternatively, the user can scroll-delete without pressing the edit button. I use a pair of Ivars to keep track of whether the table is in edit mode, or by pressing the edit button, and act accordingly (for example, updating numberOfRowsInTableView: with an extra insert line when Edit was clicked).

Everything works fine, except for the thing: when in edit mode (i.e., the user explicitly pressed the edit button, and the insert line appeared at the top), if the user tries to delete the bottom line, the next line up is deleted instead. Deleting any other line is fine.

EDIT . It seems to delete the line above, but if I immediately quit and restart the application, it appears that the bottom line has passed. Therefore, I assume that my UITableView does not synchronize with my NSFetchedResultsController somewhere.

Here is the code I'm using:

#import "ChecklistsViewController.h" #import "Checklist.h" @interface ChecklistsViewController (private) - (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath; - (void)addingView; @end @implementation ChecklistsViewController @synthesize category, managedObjectContext, fetchedResultsController; - (id)initWithStyle:(UITableViewStyle)style { self = [super initWithStyle:style]; if (self) { editingFromSwipe = NO; tableIsEditing = NO; } return self; } - (void)dealloc { [category release]; [managedObjectContext release]; [fetchedResultsController release]; [super dealloc]; } #pragma mark - View lifecycle - (void)viewDidLoad { [super viewDidLoad]; editingFromSwipe = NO; tableIsEditing = NO; self.navigationItem.rightBarButtonItem = self.editButtonItem; self.tableView.allowsSelectionDuringEditing = YES; } - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { // Return YES for supported orientations return (interfaceOrientation == UIInterfaceOrientationPortrait); } #pragma mark - Table view data source - (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView { return [[self.fetchedResultsController sections] count]; } - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { id <NSFetchedResultsSectionInfo> sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:section]; int rows = [sectionInfo numberOfObjects]; if (self.editing) { if (!editingFromSwipe && tableIsEditing) { return rows +1; } return rows; } tableIsEditing = NO; return rows; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier]; if (cell == nil) { cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:CellIdentifier] autorelease]; } // Configure the cell... cell.accessoryType = UITableViewCellAccessoryDisclosureIndicator; NSLog(@"Should go into if statement here! \n"); if (tableView.editing) { // if ((indexPath.row == 0) && (!editingFromSwipe)) { NSLog(@"Configuring Add Button Cell while editing \n"); cell.textLabel.text = @"Add New Checklist"; cell.detailTextLabel.text = nil; } else { NSLog(@"Configuring other cells while editing \n"); [self configureCell:cell atIndexPath:indexPath]; } } else { NSLog(@"Configuring Cell Normally While Not Editing \n"); [self configureCell:cell atIndexPath:indexPath]; } return cell; } - (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath { if (editingStyle == UITableViewCellEditingStyleDelete) { // Delete the managed object for the given index path NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext]; int numberOfRows = [self tableView:tableView numberOfRowsInSection:indexPath.section]; int rowBeingDeleted = indexPath.row +1; if (tableIsEditing && !editingFromSwipe && numberOfRows == rowBeingDeleted) { [context deleteObject:[self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:indexPath.row-1 inSection:indexPath.section]]]; } else { [context deleteObject:[self.fetchedResultsController objectAtIndexPath:indexPath]]; } // Save the context. NSError *error = nil; if (![context save:&error]) { // TO DO: Fix error code. NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } } else if (editingStyle == UITableViewCellEditingStyleInsert) { [self addingView]; } } - (UITableViewCellEditingStyle)tableView:(UITableView *)tableView editingStyleForRowAtIndexPath:(NSIndexPath *)indexPath { int row = indexPath.row; if (self.editing && row == 0) { if (!editingFromSwipe && tableIsEditing) { return UITableViewCellEditingStyleInsert; } else if (editingFromSwipe) { return UITableViewCellEditingStyleDelete; } } return UITableViewCellEditingStyleDelete; } - (void)tableView:(UITableView *)tableView willBeginEditingRowAtIndexPath:(NSIndexPath *)indexPath { editingFromSwipe = YES; [super tableView:tableView willBeginEditingRowAtIndexPath:indexPath]; } - (void)tableView:(UITableView *)tableView didEndEditingRowAtIndexPath:(NSIndexPath *)indexPath { [super tableView:tableView didEndEditingRowAtIndexPath:indexPath]; editingFromSwipe = NO; } - (void)setEditing:(BOOL)editing animated:(BOOL)animated { [super setEditing:editing animated:animated]; NSArray *addRow = [NSArray arrayWithObjects:[NSIndexPath indexPathForRow:0 inSection:0], nil]; [self.tableView beginUpdates]; if (!editingFromSwipe) { if (editing) { tableIsEditing = YES; [self.tableView insertRowsAtIndexPaths:addRow withRowAnimation:UITableViewRowAnimationLeft]; } else { [self.tableView deleteRowsAtIndexPaths:addRow withRowAnimation:UITableViewRowAnimationLeft]; } } [self.tableView endUpdates]; } #pragma mark - Table view delegate - (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath { if (indexPath.row != 0) { TO DO: Code for when row is selected } } #pragma mark - Data - (void)configureCell:(UITableViewCell *)cell atIndexPath:(NSIndexPath *)indexPath { Checklist *aChecklist = [self.fetchedResultsController objectAtIndexPath:indexPath]; cell.textLabel.text = aChecklist.name; cell.detailTextLabel.text = aChecklist.category.name; } - (void) addingView// :(id)sender { AddingViewController *viewController = [[AddingViewController alloc] initWithNibName:@"AddingViewController" bundle:nil]; viewController.delegate = self; viewController.title = @"Add Checklist"; // Create the navigation controller and present it modally UINavigationController *navigationController = [[UINavigationController alloc] initWithRootViewController:viewController]; [self presentModalViewController:navigationController animated:YES]; viewController.textLabel.text = @"Enter new checklist name"; [navigationController release]; [viewController release]; } #pragma mark - AddingViewDelegate - (void)addingViewController:(AddingViewController *)addingViewController didAdd:(NSString *)itemAdded { if (itemAdded != nil) { // Turn off editing mode. if (self.editing) [self.navigationController setEditing:NO animated:NO]; // Add the category name to our model and table view. // Create a new instance of the entity managed by the fetched results controller. NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext]; NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity]; Checklist *newChecklist = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context]; [category addChecklistsObject:newChecklist]; newChecklist.name = itemAdded; // [newChecklist setDateStamp:[NSDate date]]; // Save the context. NSError *error = nil; if (![context save:&error]) { TO DO: fix error code. NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } } [self dismissModalViewControllerAnimated:YES]; } #pragma mark - Fetched results controller - (NSFetchedResultsController *)fetchedResultsController { if (fetchedResultsController != nil) { return fetchedResultsController; } // Set up the fetched results controller. // Create the fetch request for the entity. NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; // Edit the entity name as appropriate. NSEntityDescription *entity = [NSEntityDescription entityForName:@"Checklist" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entity]; // Set 4* the predicate so we only see checklists for this category. NSPredicate *requestPredicate = [NSPredicate predicateWithFormat:@"category.name = %@", self.category.name]; [fetchRequest setPredicate:requestPredicate]; // Set the batch size to a suitable number. [fetchRequest setFetchBatchSize:20]; // Edit the sort key as appropriate. NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:YES]; NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil]; [fetchRequest setSortDescriptors:sortDescriptors]; // Edit the section name key path and cache name if appropriate. // nil for section name key path means "no sections". NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; [aFetchedResultsController release]; [fetchRequest release]; [sortDescriptor release]; [sortDescriptors release]; NSError *error = nil; if (![self.fetchedResultsController performFetch:&error]) { // TO DO: error stuff NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } return fetchedResultsController; } #pragma mark - Fetched results controller delegate - (void)controllerWillChangeContent:(NSFetchedResultsController *)controller { [self.tableView beginUpdates]; } - (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type { switch(type) { case NSFetchedResultsChangeInsert: [self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { UITableView *tableView = self.tableView; switch(type) { case NSFetchedResultsChangeInsert: [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeUpdate: [self configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; break; case NSFetchedResultsChangeMove: [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller { [self.tableView endUpdates]; } @end 

Answer 1

Your design is to blame. You should not add rows anywhere except by logging into the table.

The entire point of the selected result controller (FRC) should synchronize the table view with the data. The order of the rows in the table should reflect the order of the managed objects in the fetchedObjects array. Inserting a row at the bottom or top and adding an object that does not necessarily logically belong to the top or bottom of the table violates this synchronization.

When you add a new managed entity to addingViewController:didAdd: FRC alerts the delegate who is trying to redraw the table. You tried to compensate for this, but you really cannot. All indices break down.

Instead of using a line to enter new lines. Use the table header or footer view. Thus, you can freeze the table view, create a new object, and then update the table, and the new object will be displayed where it logically belongs in the table.

Answer 2

You can add static cells to UITableViews that get their data from NSFetchedResultsController. But for this you need to configure almost all of the NSIndexPath that are used in one of the UITableViewDelegate , UITableViewDataSource or NSFetchedResultsControllerDelegate .

I added some helper methods that translate the index path in the tableview to the index path of the resulting result controller and vice versa. Something like this can be used if you want to add a line at the top:

 - (NSIndexPath *)tableIndexPathFromNSFRCIndexPath:(NSIndexPath *)ip { if (editingMode && ip.section == 0) { NSIndexPath *newIP = [NSIndexPath indexPathForRow:ip.row+1 inSection:ip.section]; return newIP; } return ip; } - (NSIndexPath *)nsfrcIndexPathFromTableIndexPath:(NSIndexPath *)ip { if (editingMode && ip.section == 0) { NSIndexPath *newIP = [NSIndexPath indexPathForRow:ip.row-1 inSection:ip.section]; return newIP; } return ip; } 

and then you must change each method that passes the index path from the table to the fetchedresultscontroller or from frc to the table. As an example, I will show you two.

 - (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath { newIndexPath = [self tableIndexPathFromNSFRCIndexPath:newIndexPath]; indexPath = [self tableIndexPathFromNSFRCIndexPath:indexPath]; switch(type) { case NSFetchedResultsChangeInsert: [self.listTableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeDelete: [self.listTableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; break; case NSFetchedResultsChangeUpdate: [self configureCell:[self.listTableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath]; break; case NSFetchedResultsChangeMove: [self.listTableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; [self.listTableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade]; break; } } - (void)tableView:(UITableView *)aTableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{ [aTableView deselectRowAtIndexPath:indexPath animated:YES]; if (editingMode && indexPath.section == 0 && indexPath.row == 0) { // Add New entry... } else { indexPath = [self nsfrcIndexPathFromTableIndexPath:indexPath]; NSManagedObject *selectedObject = [self.fetchedResultsController objectAtIndexPath:indexPath]); } } 

Answer 3

In order not to mix the lines, I would suggest putting the insert line in my section. Since you obviously use only one section, you know that the section you submit to FRC should always be 0. The code will be as simple as:

 [context deleteObject:[self.fetchedResultsController objectAtIndexPath:[NSIndexPath indexPathForRow:indexPath.row inSection:0]]]; 

The TechZen solution will also work, so the solution you choose depends entirely on which design you prefer. The TechZen solution does not prevent you from having multiple partitions, but this solution can be modified to support multiple partitions.