Question

我有一个名为GarmentTypes的Core Data实体显示在UITableViewController子类中，它实现了NSFetchedResultsControllerDelegate，并且有一个NSFetchedResultsController作为属性。模态seque提供了一个新的视图控制器，可以添加新的GarmentType。解除模态视图控制器后，底层的UITableViewController不会更新。我知道GarmentType实体保存在数据库中，因为如果我退回到前一个视图控制器然后重新设置，则显示它。您可以在此处观看视频演示：https://www.youtube.com/watch?v=DahKMgVxDho

我创建了一个名为CoreDataTableViewController的泛型类，它实现了NSFetchedResultsControllerDelegate并具有NSFetchedResultsController属性：

@interface CoreDataTableViewController : UITableViewController <NSFetchedResultsControllerDelegate>
@property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;

我将CoreDataTableViewController子类化为GarmentTypesCDTVC以显示GarmentTypes。它有一个属性，NSManagedObjectContext：

@interface GarmentTypesCDTVC : CoreDataTableViewController
@property (strong, nonatomic) NSManagedObjectContext *context;

在viewWillAppear：

中检索上下文

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

    [DressyHelper openDocumentUsingBlock:^(UIManagedDocument *document){
        self.context = document.managedObjectContext;
    }];
}

获取请求是在上下文的setter时创建的：

- (void)setContext:(NSManagedObjectContext *)context
{
    _context = context;
    if (context) {
        NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"GarmentType"];
        request.sortDescriptors = @[[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(localizedCaseInsensitiveCompare:)]];
        request.predicate       = nil; // All GarmentTypes
        self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:context sectionNameKeyPath:nil cacheName:nil];
    } else {
        self.fetchedResultsController = nil;
    }
}

DressyHelper分发了UIManagedDocument：

// Open or create a UIManagedDocument.
+ (void)openDocumentUsingBlock:(completion_block_t)completionBlock;
{
    // Get documents directory and path.
    NSURL *url = [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
    url        = [url URLByAppendingPathComponent:@"DressyDocument"];

    // Create the document and open if a match exists on file.
    UIManagedDocument *document = [[UIManagedDocument alloc] initWithFileURL:url];
    if ([[NSFileManager defaultManager] fileExistsAtPath:[url path]]) {
        [document openWithCompletionHandler:^(BOOL success) {
            if (!success) NSLog (@"Couldn't open document at %@", url);
            else completionBlock(document);
        }];
    } else {

        // No match exists, so save the document to file.
        [document saveToURL:url forSaveOperation:UIDocumentSaveForCreating completionHandler:^(BOOL success) {
            if (!success) NSLog(@"Couldn't create document at %@", url);
            else completionBlock(document);
        }];
    }
}

我已经阅读了类似的问题并试图实施但没有成功，所以我很抱歉，如果事实证明这需要一个类似的解决方案，但我已经在这方面绞尽脑汁一段时间了。例如，放置一个[self.tableView reloadData];在GarmenttypesCDTV的观点中会发现：没有效果。

TIA

更新：这是CoreDataTableViewController的.m：

//
//  CoreDataTableViewController.m
//  Dressy
//
//  Created by Michael Mangold on 9/6/13.
//  Copyright (c) 2013 Michael Mangold. All rights reserved.
//

#import "CoreDataTableViewController.h"

@interface CoreDataTableViewController()
@property (nonatomic) BOOL beganUpdates;
@end

@implementation CoreDataTableViewController

#pragma mark - Properties

@synthesize fetchedResultsController = _fetchedResultsController;
@synthesize suspendAutomaticTrackingOfChangesInManagedObjectContext = _suspendAutomaticTrackingOfChangesInManagedObjectContext;
@synthesize debug = _debug;
@synthesize beganUpdates = _beganUpdates;

#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.suspendAutomaticTrackingOfChangesInManagedObjectContext) {
        [self.tableView beginUpdates];
        self.beganUpdates = YES;
    }
}

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex
     forChangeType:(NSFetchedResultsChangeType)type
{
    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.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.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];
    }
}

@end

Answer 1

创建NSFetchedResultsController后，您实际上并未设置其委托。

//在此之后

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

//添加此

self.fetchedResultsController.delegate = self;

您还需要实施一些NSFetchedResultsControllerDelegate和UITableViewDelegate方法。 Apple has docs on how to do this.

Answer 2

我通过将上下文传递给表视图控制器来修复了问题，该控制器添加了新的GarmentType。我一直在调用我的助手类'openDocumentUsingBlock：再次获取上下文。我假设我使用上下文的新实例是安全的，因为它是同一个UIManagedDocument的属性。猜猜我错了。感谢那些回复的人。

NSFetchedResultsController从模态视图控制器返回时不更新

2 个答案: