为什么 Core Data 不获取我的数据？

Question

我的实体属性数据在重新启动时未获取或在退出前未保存（可能是任何一种情况）。最重要的是，重新启动时数据未显示在表中。我想我可能需要整合我的核心数据方法或将它们移动到应用程序委托文件中。

我认为我的核心数据代码都搞砸了，谁能帮忙修复它？ 如果您需要从 appdelegate.m 等中查看任何其他代码，请告诉我。 这是我的视图控制器的代码：

#import "RoutineTableViewController.h"
#import "AlertPrompt.h"
#import "Routine.h"
#import "CurlAppDelegate.h"

@implementation RoutineTableViewController

@synthesize tableView;
@synthesize eventsArray;
@synthesize managedObjectContext;

- (void)dealloc
{
    [managedObjectContext release];
    [eventsArray release];
    [super dealloc];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
}

- (NSManagedObjectContext *) managedObjectContext {

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

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

-(void)addEvent
{
    Routine *routine = (Routine *)[NSEntityDescription insertNewObjectForEntityForName:@"Routine" inManagedObjectContext:managedObjectContext];

    CurlAppDelegate *curlAppDelegate = [[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *context = [curlAppDelegate managedObjectContext];

    NSManagedObject *newRoutineEntry;

    newRoutineEntry = [NSEntityDescription insertNewObjectForEntityForName:@"Routine" inManagedObjectContext:context];


    NSError *error = nil;
    if (![managedObjectContext save:&error]) {
        // Handle the error.
    }

    [eventsArray insertObject:routine atIndex:0];
    NSIndexPath *indexPath = [NSIndexPath indexPathForRow:0 inSection:0];
    [self.tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
    [self.tableView scrollToRowAtIndexPath:[NSIndexPath indexPathForRow:0 inSection:0] atScrollPosition:UITableViewScrollPositionTop animated:YES];
}

#pragma mark - View lifecycle

- (void)viewDidLoad
{
    CurlAppDelegate *curlAppDelegate = [[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = [curlAppDelegate managedObjectContext];

    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Routine" inManagedObjectContext:context];
    [request setEntity:entity];

    NSError *error = nil;
    NSMutableArray *mutableFetchResults = [[context executeFetchRequest:request error:&error] mutableCopy];
    if (mutableFetchResults == nil) {
        // Handle the error.
    }
    [self setEventsArray:mutableFetchResults];
    [mutableFetchResults release];
    [request release];

    UIBarButtonItem * addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:@selector(showPrompt)];
    [self.navigationItem setLeftBarButtonItem:addButton];
    [addButton release];

    UIBarButtonItem *editButton = [[UIBarButtonItem alloc]initWithTitle:@"Edit" style:UIBarButtonItemStyleBordered target:self action:@selector(toggleEdit)];
    self.navigationItem.rightBarButtonItem = editButton;
    [editButton release];

    [super viewDidLoad];
}

-(void)toggleEdit
{
    [self.tableView setEditing: !self.tableView.editing animated:YES];

    if (self.tableView.editing)
        [self.navigationItem.rightBarButtonItem setTitle:@"Done"];
    else
        [self.navigationItem.rightBarButtonItem setTitle:@"Edit"];
}

-(void)showPrompt
{
    AlertPrompt *prompt = [AlertPrompt alloc];
    prompt = [prompt initWithTitle:@"Add Workout Day" message:@"\n \n Please enter title for workout day" delegate:self cancelButtonTitle:@"Cancel" okButtonTitle:@"Add"];
    [prompt show];
    [prompt release];
}

- (void)alertView:(UIAlertView *)alertView willDismissWithButtonIndex:(NSInteger)buttonIndex
{
    if (buttonIndex != [alertView cancelButtonIndex])
    {
        NSString *entered = [(AlertPrompt *)alertView enteredText];
        if(eventsArray && entered)
        {
            [eventsArray addObject:entered];
            [tableView reloadData];
        }
    }
}

- (void)viewDidUnload
{
    self.eventsArray = nil;
    [super viewDidUnload];
}

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

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

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

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

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

#pragma mark - Table view data source

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
    return 1;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section
{
    return [eventsArray count];
}

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

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil)
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellEditingStyleDelete reuseIdentifier:CellIdentifier] autorelease];
    cell.textLabel.text = [self.eventsArray objectAtIndex:indexPath.row];

    return cell;
}
// Override to support conditional editing of the table view.
- (BOOL)tableView:(UITableView *)tableView canEditRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Return NO if you do not want the specified item to be editable.
    return YES;
}

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

     if (editingStyle == UITableViewCellEditingStyleDelete) {

         // Delete the managed object at the given index path.
         NSManagedObject *eventToDelete = [eventsArray objectAtIndex:indexPath.row];
         [managedObjectContext deleteObject:eventToDelete];

         // Update the array and table view.
         [eventsArray removeObjectAtIndex:indexPath.row];
         [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:YES];

         // Commit the change.
         NSError *error = nil;
         if (![managedObjectContext save:&error]) {
             // Handle the error.
         }
     }
 }
@end

这是数据模型：

编辑：

添加了 PersisentStoreCoordinater 方法（来自 App Delegate）：

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil)
    {
        return __persistentStoreCoordinator;
    }

    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Curl.sqlite"];

    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error])
    {
        /*
         Replace this implementation with code to handle the error appropriately.

         abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.

         Typical reasons for an error here include:
         * The persistent store is not accessible;
         * The schema for the persistent store is incompatible with current managed object model.
         Check the error message to determine what the actual problem was.


         If the persistent store is not accessible, there is typically something wrong with the file path. Often, a file URL is pointing into the application's resources directory instead of a writeable directory.

         If you encounter schema incompatibility errors during development, you can reduce their frequency by:
         * Simply deleting the existing store:
         [[NSFileManager defaultManager] removeItemAtURL:storeURL error:nil]

         * Performing automatic lightweight migration by passing the following dictionary as the options parameter: 
         [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

         Lightweight migration will only work for a limited set of schema changes; consult "Core Data Model Versioning and Data Migration Programming Guide" for details.

         */
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}

Answer 1

这里有几个技巧可以解决这个问题：

1. 在您的 RoutineViewController 中删除对 managedObjectContext 等的所有引用。仅引用 AppDelegate 中的 CoreData 类/属性。
2. 当您需要引用时（例如在您的 AddEvent 方法中）从您的委托中引用适当的对象（参见下面的代码）

3. 当这变得更加复杂时，您可能需要一个处理所有 CoreData 对象的 DataManager 类。将其设为 Singleton，您将能够在任何类中引用它。为了获取显示的对象，您可以在此类中创建必要的方法以在 NSMutableArray 中检索这些对象

   CurlAppDelegate *curlAppDelegate = [[UIApplication sharedApplication] 委托]; NSManagedObjectContext *context = [curlAppDelegate managedObjectContext];

   Routine *routine = (Routine *)[NSEntityDescription insertNewObjectForEntityForName:@"Routine" inManagedObjectContext:context];

看看您现在是如何使用来自 AppDelegate 的上下文而不是本地的？这很重要，因为您的应用会在初始化时将您的 xdatamodel 从您的 Bundle 链接到您的 AppDelegate。

如果您担心数据未被保存或覆盖，请查看您的 AppDelegate 的 - (NSPersistentStoreCoordinator *)persistentStoreCoordinator

当您退出并进入应用程序时，设置恰好链接到您存储的数据库。这是加载到 Curl.sqlite 文件中的 AppDelegate 中的代码（已修改）：

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator{
if (__persistentStoreCoordinator != nil)
{
    return __persistentStoreCoordinator;
}

NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"Curl.sqlite"];

NSError *error = nil;
__persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error])
{

    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
}    

return __persistentStoreCoordinator;

}

Answer 2

我的猜测是您正在混淆您的托管对象上下文。插入一个并尝试保存另一个。在您的视图控制器中删除您的核心数据相关方法，然后尝试通过您的应用程序委托方法。然后数据将被正确保存，或者Core Data会抛出错误。确保检查您的 Core Data 代码中的任何设置/保存错误。

Answer 3

您是否已将核心数据文件附加到主包中？ iPhone 应用中有两种类型的 Bundle。主包和应用程序包。我们有一个类似你的场景。我们将数据库复制到我们的主包中，并将数据库的位置写入我们的代码中。然后它工作正常。你也可以检查这个问题。