Question

我有UITableViewController个任务项，使用Apple的NSFetchedResultsController（子类）模板通过CoreDataTableViewController连接到Core Data。 TVC打开detailViewController，处理编辑和保存。

有时当我在Core Data中保存任务并编辑一个任务然后保存它时，detailViewController会保存数据并返回到TVC，但tableView根本没有显示任何记录，它只是空的。当我杀死应用程序并再次运行它时，所有任务都会按预期显示。

这是非常罕见的行为，因此很难跟踪和调试。在极少数情况下，有没有人有什么想法导致空tableView？

在DetailVC.m

- (void)save
{
    if (self.editingTask) {
        [[DataManager sharedInstance] updateItem:self.editingTask withText:self.textField.text date:self.datePicker.date priority:self.segmentedControl.selectedSegmentIndex completed:NO];
    } else {
        [[DataManager sharedInstance] saveNewItem:self.textField.text date:self.datePicker.date priority:self.segmentedControl.selectedSegmentIndex];
    }
    [self.navigationController popViewControllerAnimated:YES];
}

在DataManager.m

- (CoreDataStatus)updateItem:(Task *)editingTask withText:(NSString *)text date:(NSDate *)date priority:(NSUInteger)priority completed:(BOOL)completed
{
    AppDelegate *appDelegate = [[UIApplication sharedApplication] delegate];

    Task *taskToUpdate = editingTask;
    taskToUpdate.due = date;
    taskToUpdate.text = text;
    taskToUpdate.priority = [NSNumber numberWithInteger:priority];
    taskToUpdate.completed = [NSNumber numberWithBool:completed];

    // save
    NSError *error = nil;
    [appDelegate.managedObjectContext save:&error];

    if (!error) {

        [self updateNotificationsAndBadgeCount];
        return Success;
    } else {
        return Error;
    }
}

在TVC.m

- (void)awakeFromNib
{
    self.managedObjectContext = self.appDelegate.managedObjectContext;
}

- (void)setManagedObjectContext:(NSManagedObjectContext *)managedObjectContext
{
    _managedObjectContext = managedObjectContext;

    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Task"];
    request.predicate = [NSPredicate predicateWithFormat:@"completed = %@", [NSNumber numberWithBool:NO]];
    request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"due" ascending:YES]];

    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:nil];
}

在CoreDataTableViewController.m

中

- (void)performFetch
{
    if (self.fetchedResultsController) {
        if (self.fetchedResultsController.fetchRequest.predicate) {
            if (self.debug) NSLog(@"[%@ %@] fetching %@ with predicate: %@", NSStringFromClass([self class]), NSStringFromSelector(_cmd), self.fetchedResultsController.fetchRequest.entityName, self.fetchedResultsController.fetchRequest.predicate);
        } else {
            if (self.debug) NSLog(@"[%@ %@] fetching all %@ (i.e., no predicate)", NSStringFromClass([self class]), NSStringFromSelector(_cmd), self.fetchedResultsController.fetchRequest.entityName);
        }
        NSError *error;
        BOOL success = [self.fetchedResultsController performFetch:&error];
        if (!success) NSLog(@"[%@ %@] performFetch: failed", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
        if (error) NSLog(@"[%@ %@] %@ (%@)", NSStringFromClass([self class]), NSStringFromSelector(_cmd), [error localizedDescription], [error localizedFailureReason]);
    } else {
        if (self.debug) NSLog(@"[%@ %@] no NSFetchedResultsController (yet?)", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
    }
    [self.tableView reloadData];
}

偶尔使用NSFetchedResultsController清空tableView

0 个答案: