iphone - 我的Core Data代码有问题吗

Question

一位客户就我的应用程序中的错误与我联系，我认为该错误与我对 Core Data 的使用有关。目前这只是一个理论，因为我自己无法重现该问题。

问题似乎是，如果用户创建一个新的实体对象，然后立即编辑该实体对象，它似乎不会正确保留，并且下次用户打开应用程序时，该对象不存在。

如果用户创建实体对象并退出应用程序而不对其进行编辑，则不会发生该问题，如果用户在重新打开应用程序后编辑该对象，也不会发生该问题。

我只收到过一份有关此情况发生的报告，并且相关设备是运行 IOS4.0.2 的 iPhone 3G。我无法在 iPhone 3GS、iPhone 4 或通过模拟器(均运行 4.0.2)上重新创建它

我不是核心数据专家，我想知道我使用该框架的方式是否存在问题。如果有人能检查我下面的代码并让我知道他们是否发现任何潜在的问题，我将非常感激。

我已经包含了与相关类的核心数据交互的方法。

应用程序委托(delegate)

- (void)applicationDidEnterBackground:(UIApplication *)application {

    NSError *error = nil;
    if (managedObjectContext_ != nil) {
        if ([managedObjectContext_ hasChanges] && ![managedObjectContext_ save:&error]) {
            // log
        } 
    }
}

- (void)applicationWillTerminate:(UIApplication *)application {

    NSError *error = nil;
    if (managedObjectContext_ != nil) {
        if ([managedObjectContext_ hasChanges] && ![managedObjectContext_ save:&error]) {
            // log
        } 
    }
}

- (NSManagedObjectContext *)managedObjectContext {

    if (managedObjectContext_ != nil) {
        return managedObjectContext_;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        managedObjectContext_ = [[NSManagedObjectContext alloc] init];
        [managedObjectContext_ setPersistentStoreCoordinator:coordinator];
    }
    return managedObjectContext_;
}

- (NSManagedObjectModel *)managedObjectModel {

    if (managedObjectModel_ != nil) {
        return managedObjectModel_;
    }
    managedObjectModel_ = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];    
    return managedObjectModel_;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {

    if (persistentStoreCoordinator_ != nil) {
        return persistentStoreCoordinator_;
    }

    NSURL *storeURL = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory] stringByAppendingPathComponent: @"mydatabase.sqlite"]];

    NSError *error = nil;
    persistentStoreCoordinator_ = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
        NSLog(@"An error occurred adding the persistentStoreCoordinator. %@, %@", error, [error userInfo]);
        // Display an alert message if an error occurs
    }    

    return persistentStoreCoordinator_;
}

Controller 1(使用通过图像选择器选择的图像创建实体对象)

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info {

    UIImage* selectedImage = [info objectForKey:UIImagePickerControllerOriginalImage];

    // Create an image object for the new image.
    NSManagedObject *image = [NSEntityDescription insertNewObjectForEntityForName:@"Image" inManagedObjectContext:managedObjectContext];

    // Set the image for the image managed object.
    [image setValue:[selectedImage scaleAndCropImageToScreenSize] forKey:@"image"];

    // Create a thumbnail version of the image.
    UIImage *imageThumbnail = [selectedImage thumbnailImage:50.0F];

    // Create a new note
    Note *note = [NSEntityDescription insertNewObjectForEntityForName:@"Note" inManagedObjectContext:managedObjectContext];
    NSDate *now = [[NSDate alloc] init];
    note.createdDate = now;
    note.lastModifiedDate = now;
    [now release];
    note.thumbnail = imageThumbnail;
    note.image = image;
    }

    [self dismissModalViewControllerAnimated:YES];
    [picker release];
}

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath {
    NotePadViewController *notePadController = [[NotePadViewController alloc] initWithNibName:@"NotePadView" bundle:nil];
    Note *note = [[self fetchedResultsController] objectAtIndexPath:indexPath];
    notePadController.note = note;
    notePadController.title = note.notes;
    [self.navigationController pushViewController:notePadController animated:YES];
    [notePadController release];
}

- (NSFetchedResultsController *)fetchedResultsController {

    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Note" inManagedObjectContext:managedObjectContext];
    [fetchRequest setEntity:entity];

    [fetchRequest setFetchBatchSize:20];
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"createdDate" ascending:NO];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [fetchRequest setSortDescriptors:sortDescriptors];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:managedObjectContext sectionNameKeyPath:nil cacheName:@"Root"];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;

    [aFetchedResultsController release];
    [fetchRequest release];
    [sortDescriptor release];
    [sortDescriptors release];

    NSError *error = nil;
    if (![fetchedResultsController performFetch:&error]) {
        NSLog(@"An error occured retrieving fetched results. %@, %@", error, [error userInfo]);
        // Display an alert message if an error occurs
    }

    return fetchedResultsController;
}    

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    [self.tableView beginUpdates];
}

- (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 reloadSections:[NSIndexSet indexSetWithIndex:newIndexPath.section] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

- (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)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    [self setControllerTitle];
    [self.tableView endUpdates];
}

Controller 2 - 用于查看和编辑实体对象(添加文本)

- (void)saveAction:(id)sender {

    NSDate *now = [[NSDate alloc] init];

    if (self.note != nil && textView.text.length == 0) {
        self.note.notes = nil;
        self.note.lastModifiedDate = now;
    } else if (textView.text.length != 0) {
        // Create a new note if one does not exist
        if (self.note == nil) {
            VisualNotesAppDelegate *appDelegate = (VisualNotesAppDelegate *)[[UIApplication sharedApplication] delegate];
            NSManagedObjectContext *managedObjectContext = appDelegate.managedObjectContext;
            Note *newNote = [NSEntityDescription insertNewObjectForEntityForName:@"Note" inManagedObjectContext:managedObjectContext];
            self.note = newNote;
            self.note.createdDate = now;
        }
        self.note.lastModifiedDate = now;
        self.note.notes = textView.text;
        self.title = [note title]; 
    }

    [now release];

    [self.textView resignFirstResponder];
}

提前非常感谢。

Answer 1

首先，您确实不应该忽略这些错误。您可能会在那里抛出一个错误，但您却永远不知道。

代码本身没有什么真正跳出来的，但在保存过程中很容易出现错误，可能是未设置非可选参数等。

处理异常并从那里查看。