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刪除核心數據實體的最后一條記錄時,為什么我的應用程序崩潰了?

[英]Why do my app crashed when I delete the last record of a core data entity?

在我的應用程序中,我使用表視圖中顯示的兩個核心數據實體,如果有多個記錄,則可以毫無問題地將其刪除,但是如果只有一個記錄,則觸摸刪除按鈕后,應用程序將崩潰:

這是我的代碼(如果需要)來檢測問題,請提前感謝:

#import "PersonsTVC.h"
#import "Person.h"

@implementation PersonsTVC
@synthesize fetchedResultsController = __fetchedResultsController;
@synthesize managedObjectContext = __managedObjectContext;
@synthesize selectedPerson;
@synthesize searchResults,titulosseccion;



- (void)setupFetchedResultsController
{
    // 1 - Decide what Entity you want
    NSString *entityName = @"Person"; // Put your entity name here
    NSLog(@"Setting up a Fetched Results Controller for the Entity named %@", entityName);

    // 2 - Request that Entity
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:entityName];

    // 3 - Filter it if you want
    //request.predicate = [NSPredicate predicateWithFormat:@"Person.name = Blah"];

    // 4 - Sort it if you want
    // First sort descriptor (required for grouping into sections):
    NSSortDescriptor *sortByDate = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:NO];
    // Second sort descriptor (for the items within each section):
    NSSortDescriptor *sortByName = [[NSSortDescriptor alloc] initWithKey:@"firstname" ascending:YES];
    [request setSortDescriptors:@[sortByDate, sortByName]];


   //
   // request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"firstname"
                                                                                     //ascending:YES
                                                                                      //selector:@selector(localizedCaseInsensitiveCompare:)]];
    // 5 - Fetch it
    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request
                                                                        managedObjectContext:self.managedObjectContext
                                                                          sectionNameKeyPath:@"sectionIdentifier"
                                                                                   cacheName:nil];
    [self performFetch];
}




- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    id <NSFetchedResultsSectionInfo> theSection = [[self.fetchedResultsController sections] objectAtIndex:section];

    NSString *sectionName = [theSection name];
    if ([sectionName isEqualToString:@"0"]) {
        return @"Today";
    } else if ([sectionName isEqualToString:@"1"]) {
        return @"Tomorrow";
    }
    else if ([sectionName isEqualToString:@"2"]) {
        return @"Upcoming";
    }
    return @"Other";
}




- (void) viewDidLoad
{



    self.searchResults = [NSMutableArray arrayWithCapacity:[[self.fetchedResultsController fetchedObjects] count]];
    [self.tableView reloadData];
}








- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    [self setupFetchedResultsController];
}




- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{

    // Perform segue to detail when a SEARCH table cell is touched
    if(tableView == self.searchDisplayController.searchResultsTableView)
    {
        [self performSegueWithIdentifier:@"Person Detail Segue" sender:tableView];
    }

}



- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    static NSString *CellIdentifier = @"Persons Cell";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) {
        cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:CellIdentifier];
    }

    // Configure the cell...
    // Configure the cell...
    Person  *person = nil;

    if (tableView == self.searchDisplayController.searchResultsTableView)
    {
        NSLog(@"Configuring cell to show search results");
        person = [self.searchResults objectAtIndex:indexPath.row];
    }
    else
    {
        NSLog(@"Configuring cell to show normal data");
        person = [self.fetchedResultsController objectAtIndexPath:indexPath];
    }








    NSString *fullname = [NSString stringWithFormat:@"%@ %@", person.firstname, person.surname];
    cell.textLabel.text = person.firstname;
    if ([person.inRole.color isEqual :@"Yellow"])
    {
        cell.imageView.image = [UIImage imageNamed:@"Yellow"];
    }
    if ([person.inRole.color isEqual :@"Black"])
    {
        cell.imageView.image = [UIImage imageNamed:@"Black"];
    }
    if ([person.inRole.color isEqual :@"Grey"])
    {
        cell.imageView.image = [UIImage imageNamed:@"Grey"];
    }
    if ([person.inRole.color isEqual :@"Red"])
    {
        cell.imageView.image = [UIImage imageNamed:@"Red"];
    }
    if ([person.inRole.color isEqual :@"Blue"])
    {
        cell.imageView.image = [UIImage imageNamed:@"Blue"];
    }
    if ([person.inRole.color isEqual :@"Dark Green"])
    {
        cell.imageView.image = [UIImage imageNamed:@"DarkGreen"];
    }
    if ([person.inRole.color isEqual :@"Light Green"])
    {
        cell.imageView.image = [UIImage imageNamed:@"LightGreen"];
    }
    if ([person.inRole.color isEqual :@"Light Blue"])
    {
        cell.imageView.image = [UIImage imageNamed:@"LightBlue"];
    }
    if ([person.inRole.color isEqual :@"Brown"])
    {
        cell.imageView.image = [UIImage imageNamed:@"Brown"];
    }
    if ([person.inRole.color isEqual :@"Dark Orange"])
    {
        cell.imageView.image = [UIImage imageNamed:@"DarkOrange"];



    }

    NSDate *fechasinformat = person.date;
    NSString *fecha0 = [NSString stringWithFormat:@"%@", fechasinformat];


   cell.detailTextLabel.text = fecha0;



    return cell;
}


- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    if (tableView == self.searchDisplayController.searchResultsTableView)
    {
        return [self.searchResults count];
    }
    else
    {
        return [[[self.fetchedResultsController sections] objectAtIndex:section] numberOfObjects];
    }
}


- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {

    if (editingStyle == UITableViewCellEditingStyleDelete) {

        [self.tableView beginUpdates]; // Avoid  NSInternalInconsistencyException

        // Delete the person object that was swiped
        Person *personToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
        NSLog(@"Deleting (%@)", personToDelete.firstname);
        [self.managedObjectContext deleteObject:personToDelete];
        [self.managedObjectContext save:nil];

        // Delete the (now empty) row on the table
        [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
        [self performFetch];

        [self.tableView endUpdates];
    }
}

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"Add Person Segue"])
    {
        NSLog(@"Setting PersonsTVC as a delegate of PersonDetailTVC");
        PersonDetailTVC *personDetailTVC = segue.destinationViewController;
        personDetailTVC.delegate = self;

        NSLog(@"Creating a new person and passing it to PersonDetailTVC");
        Person *newPerson = [NSEntityDescription insertNewObjectForEntityForName:@"Person"
                                                          inManagedObjectContext:self.managedObjectContext];

        personDetailTVC.person = newPerson;
    }
    else if ([segue.identifier isEqualToString:@"Person Detail Segue"])
    {
        NSLog(@"Setting PersonsTVC as a delegate of PersonDetailTVC");
        PersonDetailTVC *personDetailTVC = segue.destinationViewController;
        personDetailTVC.delegate = self;

        // Store selected Person in selectedPerson property
        if(sender == self.searchDisplayController.searchResultsTableView)
        {
            NSIndexPath *indexPath = [self.searchDisplayController.searchResultsTableView indexPathForSelectedRow];
            self.selectedPerson = [self.searchResults objectAtIndex:[indexPath row]];
        }
        else
        {
            NSIndexPath *indexPath = [self.tableView indexPathForSelectedRow];
            self.selectedPerson = [self.fetchedResultsController objectAtIndexPath:indexPath];
        }

        NSLog(@"Passing selected person (%@) to PersonDetailTVC",    self.selectedPerson.firstname);
        personDetailTVC.person = self.selectedPerson;
    }
    else
    {
        NSLog(@"Unidentified Segue Attempted!");
    }
}

- (void)theSaveButtonOnThePersonDetailTVCWasTapped:(PersonDetailTVC *)controller
{
    // do something here like refreshing the table or whatever

    // close the delegated view
    [controller.navigationController popViewControllerAnimated:YES];    
}

#pragma mark -
#pragma mark Content Filtering

-(void)filterContentForSearchText:(NSString*)searchText scope:(NSString*)scope {
    self.searchResults = [[self.fetchedResultsController fetchedObjects] filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
        Person* person = evaluatedObject;
        NSString* firstName = person.firstname;

        //searchText having length < 3 should not be considered
        if (!!searchText && [searchText length] < 3) {
            return YES;
        }

        if ([scope isEqualToString:@"All"] || [firstName isEqualToString:scope])  {
            return ([firstName rangeOfString:searchText].location != NSNotFound);
        }
        return NO; //if nothing matches
    }]];
}

#pragma mark -
#pragma mark UISearchDisplayController Delegate Methods

- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchString:(NSString *)searchString
{
    [self filterContentForSearchText:searchString scope:@"All"];
    return YES;
}

- (BOOL)searchDisplayController:(UISearchDisplayController *)controller shouldReloadTableForSearchScope:(NSInteger)searchOption
{
    [self filterContentForSearchText:[self.searchDisplayController.searchBar text] scope:@"All"];
    return YES;
}



@end

看來您永遠不會通過tableview數據源方法設置表中的節數,這應該注意以下幾點:

- (NSInteger) numberOfSectionsInTableView:(UITableView *)tableView
{
    // Return the number of sections.
    return [[self.fetchedResultsController sections] count];
}

如果這不能解決問題,我認為是由於您缺少NSFetchedResultControllerDelegate方法(至少是controllerDidChangeContent :),這是我幾天前回答的另一個問題: 更新CoreData對象無法正常工作

看看我的答案和相應的代碼,希望對您有所幫助!

一個部分不能為空,因此,當您刪除最后一行時,您也需要刪除該部分(並且不要忘記在添加第一個對象之前創建它):

// Delete the (now empty) row on the table
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];

// Delete the section if needed
if ([[[self.fetchedResultsController sections] objectAtIndex:indexPath.section] numberOfObjects] == 0)
    [self.tableView deleteSections:[NSIndexSet indexSetWithIndex:indexPath.section] withRowAnimation:UITableViewRowAnimationFade];
[self performFetch];

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