iOS，核心数据 : Sum of subcategories value not ready on viewdidload and not updated thereafter

Question

我有一个基本的数据模型。一个主要类别有几个子类别。在每个子类别中，您定义每年预算的金额。所以我想:

a) 每个主要类别的所有子类别支出的总和。b) 所有主要类别支出的总和作为总预算

但是目前这不起作用。我在 viewwillappear 方法中设置了文本字段(因为我一直希望在再次打开 View 时更新它)。首先加载总和为 0。切换到另一个 View 并返回后，显示正确的总和。之后它不会自行更新。这是为什么？

我是 Coredata 的新手。与我在这里执行的查询相比，获取的属性可能是更好的方法吗？以下是相关的代码部分:

我的主视图 Controller (这里显示所有主要类别的总预算):

- (void)viewWillAppear:(BOOL)animated
{
    //Initialize database
    [super viewWillAppear:animated];
    if(!self.budgetDatabase){
        NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentationDirectory inDomains:NSUserDomainMask] lastObject];
        [url URLByAppendingPathComponent:@"BudgetDatabase"];
        self.budgetDatabase = [[UIManagedDocument alloc]initWithFileURL:url];
    }

    //Total cost/month will be fetched and formatted
    NSNumberFormatter *numberFormatter =[[NSNumberFormatter alloc] init];
    [numberFormatter setNumberStyle:NSNumberFormatterCurrencyStyle];

    self.sumLabel.text = [[DatabaseFetches budgetPerMonthForManagedObjectContext:self.budgetDatabase.managedObjectContext] getLocalizedCurrencyString];
    [self.tableView deselectRowAtIndexPath:[self.tableView indexPathForSelectedRow] animated:YES];
}

数据库获取:

+ (NSNumber *)budgetPerMonthForManagedObjectContext:(NSManagedObjectContext *)context
{
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"MainCategory"];
    NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"position" ascending:NO];
    request.sortDescriptors = [NSArray arrayWithObject:sortDescriptor];

    NSArray *matches = [context executeFetchRequest:request error:nil];
    CostsPeriodically *totalCostPerMonth = [[CostsPeriodically alloc]init];

    for (MainCategory *mainCategory in matches) {
        for (SpendingCategory *category in mainCategory.hasSpendingCategories){
            [totalCostPerMonth addCosts:category.costPerYear];
        }
    }

    return totalCostPerMonth.sumPerMonth;
}

编辑:这些是完整的 Fetched Results Controller 设置方法:

- (void)setupFetchedResultsController
{
    NSError *error = nil;
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"MainCategory"];
    request.sortDescriptors = [NSArray arrayWithObject:[NSSortDescriptor sortDescriptorWithKey:@"position" ascending:YES]];
    [self.budgetDatabase.managedObjectContext executeFetchRequest:request error:&error];

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

-(void)useDocument
{
    if(![[NSFileManager defaultManager]fileExistsAtPath:[self.budgetDatabase.fileURL path]]){
        [self.budgetDatabase saveToURL:self.budgetDatabase.fileURL forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
            [self setupFetchedResultsController];
            //[self initializeDatabaseWithData];
        }];
    } else if (self.budgetDatabase.documentState == UIDocumentStateClosed){
        [self.budgetDatabase openWithCompletionHandler:^(BOOL success){
            [self setupFetchedResultsController];
        }];
    } else if (self.budgetDatabase.documentState == UIDocumentStateNormal){
        [self setupFetchedResultsController];
    }
}

-(void)setBudgetDatabase:(UIManagedDocument *)budgetDatabase
{
    if(_budgetDatabase != budgetDatabase){
        _budgetDatabase = budgetDatabase;
        [self useDocument];
    }
}

进一步编辑，整个 Fetched results Controller 类:

@synthesize fetchedResultsController = _fetchedResultsController;
@synthesize suspendAutomaticTrackingOfChangesInManagedObjectContext = _suspendAutomaticTrackingOfChangesInManagedObjectContext;
@synthesize debug = _debug;
@synthesize beganUpdates = _beganUpdates;
@synthesize reordering = _reordering;
@synthesize tableView = _tableView;

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return YES;
}

#pragma mark - Fetching

- (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;
        [self.fetchedResultsController performFetch:&error];
        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];
}

- (void)setFetchedResultsController:(NSFetchedResultsController *)newfrc
{
    NSFetchedResultsController *oldfrc = _fetchedResultsController;
    if (newfrc != oldfrc) {
        _fetchedResultsController = newfrc;
        newfrc.delegate = self;
        if ((!self.title || [self.title isEqualToString:oldfrc.fetchRequest.entity.name]) && (!self.navigationController || !self.navigationItem.title)) {
            self.title = newfrc.fetchRequest.entity.name;
        }
        if (newfrc) {
            if (self.debug) NSLog(@"[%@ %@] %@", NSStringFromClass([self class]), NSStringFromSelector(_cmd), oldfrc ? @"updated" : @"set");
            [self performFetch];
        } else {
            if (self.debug) NSLog(@"[%@ %@] reset to nil", NSStringFromClass([self class]), NSStringFromSelector(_cmd));
            [self.tableView reloadData];
        }
    }
}

#pragma mark - UITableViewDataSource

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

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [[[self.fetchedResultsController sections] objectAtIndex:section] numberOfObjects];
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
    return [[[self.fetchedResultsController sections] objectAtIndex:section] name];
}

- (NSInteger)tableView:(UITableView *)tableView sectionForSectionIndexTitle:(NSString *)title atIndex:(NSInteger)index
{
    return [self.fetchedResultsController sectionForSectionIndexTitle:title atIndex:index];
}

- (NSArray *)sectionIndexTitlesForTableView:(UITableView *)tableView
{
    return [self.fetchedResultsController sectionIndexTitles];
}

#pragma mark - NSFetchedResultsControllerDelegate

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    if(!self.reordering){
        if (!self.suspendAutomaticTrackingOfChangesInManagedObjectContext) {
            [self.tableView beginUpdates];
            self.beganUpdates = YES;
        }
    }
}

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex
     forChangeType:(NSFetchedResultsChangeType)type
{
    if(!self.reordering){
        if (!self.suspendAutomaticTrackingOfChangesInManagedObjectContext)
        {
            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
{
    if(!self.reordering){
        if (!self.suspendAutomaticTrackingOfChangesInManagedObjectContext)
        {
            switch(type)
            {
                case NSFetchedResultsChangeInsert:
                    [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
                    break;

                case NSFetchedResultsChangeDelete:
                    [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                    break;

                case NSFetchedResultsChangeUpdate:
                    [self.tableView reloadRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                    break;

                case NSFetchedResultsChangeMove:
                    [self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
                    [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
                    break;
            }
        }
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    if(!self.reordering){
        if (self.beganUpdates) [self.tableView endUpdates];
    }
}

- (void)endSuspensionOfUpdatesDueToContextChanges
{
    _suspendAutomaticTrackingOfChangesInManagedObjectContext = NO;
}

- (void)setSuspendAutomaticTrackingOfChangesInManagedObjectContext:(BOOL)suspend
{
    if (suspend) {
        _suspendAutomaticTrackingOfChangesInManagedObjectContext = YES;
    } else {
        [self performSelector:@selector(endSuspensionOfUpdatesDueToContextChanges) withObject:0 afterDelay:0];
    }
}

Answer 1

我认为问题在于，您只是在 UIManagedDocument 打开(异步)之前直接更新 viewWillAppear 中的 UI。因此，您需要在 OpenWithCompletionHandler 中有一个回调来更新您的 UI。创建一个类似于

的方法

- (void)displayData {
    //Total cost/month will be fetched and formatted
    NSNumberFormatter *numberFormatter =[[NSNumberFormatter alloc] init];
    [numberFormatter setNumberStyle:NSNumberFormatterCurrencyStyle];

    self.sumLabel.text = [[DatabaseFetches budgetPerMonthForManagedObjectContext:self.budgetDatabase.managedObjectContext] getLocalizedCurrencyString];
    [self.tableView deselectRowAtIndexPath:[self.tableView indexPathForSelectedRow] animated:YES];
}

并从completionHandlers中调用它

-(void)useDocument
{
    if(![[NSFileManager defaultManager]fileExistsAtPath:[self.budgetDatabase.fileURL path]]){
        [self.budgetDatabase saveToURL:self.budgetDatabase.fileURL forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
            [self setupFetchedResultsController];
            [self displayData]; ******
            //[self initializeDatabaseWithData];
        }];
    } else if (self.budgetDatabase.documentState == UIDocumentStateClosed){
        [self.budgetDatabase openWithCompletionHandler:^(BOOL success){
            [self setupFetchedResultsController];
            [self displayData]; ******
        }];
    } else if (self.budgetDatabase.documentState == UIDocumentStateNormal){
        [self setupFetchedResultsController];
        [self displayData]; ******
    }
}