为什么我无法删除 UITableView 的底行？

当用户按下“编辑”时，我的 UITableView 在顶部添加一个插入行（带有绿色加号），并将所有其他行置于删除模式（红色减号）。或者，用户可以在不按编辑按钮的情况下滑动删除。我使用几个 Ivar 来跟踪表是否处于通过滑动或按下编辑按钮的编辑模式，并采取相应的操作（例如，更新 numberOfRowsInTableView：按下“编辑”时使用额外的插入行）。

一切都完美运行，除了以下内容：在编辑模式下（即用户明确点击编辑按钮，并且插入行出现在顶部），如果用户尝试删除底行，则上一行将被删除。删除任何其他行就可以了。

EDIT -- It appears删除上面的行，但如果我立即退出并重新加载应用程序，结果发现底行毕竟已经消失了。所以我猜测我的 UITableView 与我的 NSFetchedResultsController 某处不同步。

这是我正在使用的代码：

#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

您可以将静态单元格添加到 UITableViews 中，以从 NSFetchedResultsController 获取数据。但要做到这一点，你必须调整几乎所有在其中之一中使用的 NSIndexPathsUITableViewDelegate, UITableViewDataSource or NSFetchedResultsControllerDelegate方法。

我添加了一些辅助方法，将表视图的索引路径转换为获取的结果控制器的索引路径，反之亦然。如果你想在顶部添加一行，可以使用这样的东西：

- (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;
}

然后您必须更改将索引路径从表传递到 fetchedresultscontroller 或从 frc 传递到表的每个方法。我给大家举两个例子。

- (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]);
    }
}