objective-c 核心数据 iPhone：找不到 NSManagedObjectModel

Core-Data iPhone: could not locate an NSManagedObjectModel

提问by CraigH

I am using Apple's CoreDataBooks sample project as a learning aid for core data.

我使用 Apple 的 CoreDataBooks 示例项目作为核心数据的学习辅助工具。

I modified the app so that when the app loads I show a menu page first - not the Books tableview (RootViewController).

我修改了应用程序，以便在应用程序加载时首先显示一个菜单页面 - 而不是 Books tableview (RootViewController)。

I have done the following:

我做了以下工作：

I created a menu page in interface builder (just a view with a button on it)

我在界面构建器中创建了一个菜单页面（只是一个带有按钮的视图）

The CoreDataBooksAppDelegate.h now looks like this:

CoreDataBooksAppDelegate.h 现在看起来像这样：

// for the menu
@class MenuViewController;

@interface CoreDataBooksAppDelegate : NSObject <UIApplicationDelegate> {

NSManagedObjectModel *managedObjectModel;
NSManagedObjectContext *managedObjectContext;     
NSPersistentStoreCoordinator *persistentStoreCoordinator;

UIWindow *window;
UINavigationController *navigationController;

//for the menu
MenuViewController *viewController;
}

- (IBAction)saveAction:sender;

//for the menu
@property (nonatomic, retain) IBOutlet MenuViewController *viewController;

@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator     *persistentStoreCoordinator;

@property (nonatomic, readonly) NSString *applicationDocumentsDirectory;

@property (nonatomic, retain) IBOutlet UIWindow *window;
@property (nonatomic, retain) IBOutlet UINavigationController *navigationController;

@end

The CoreDataBooksAppDelegate.m looks like this:

CoreDataBooksAppDelegate.m 看起来像这样：

#import "CoreDataBooksAppDelegate.h"
#import "RootViewController.h"
// for the menu
#import "MenuViewController.h"


@implementation CoreDataBooksAppDelegate

@synthesize window;
@synthesize navigationController;

// for the menu
@synthesize viewController;


#pragma mark -
#pragma mark Application lifecycle

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

RootViewController *rootViewController = (RootViewController   *)[navigationController  topViewController];
rootViewController.managedObjectContext = self.managedObjectContext;

// for the menu
[window addSubview:viewController.view];

// Configure and show the window
[window makeKeyAndVisible];
}

The rest of CoreDataAppDelegete.m remains unchanged.

CoreDataAppDelegete.m 的其余部分保持不变。

In the MenuViewController when the button is clicked, the following action takes place:

在 MenuViewController 中单击按钮时，会发生以下操作：

RootViewController *modalViewController1 = [[[RootViewController alloc] initWithNibName:nil bundle:nil] autorelease];  
[self presentModalViewController:modalViewController1 animated:YES];

In IB I changed the MainWindow.xib to call the MenuViewController rather than the RootViewController.

在 IB 中，我将 MainWindow.xib 更改为调用 MenuViewController 而不是 RootViewController。

So, the app loads and the menu is displayed properly with the button. Upon clicking the button the application crashes inside of the RootViewController's viewDidLoad.

因此，应用程序加载并且菜单与按钮一起正确显示。单击按钮后，应用程序在 RootViewController 的 viewDidLoad 内崩溃。

It crashes right here:

它在这里崩溃：

- (void)viewDidLoad {
[super viewDidLoad];
NSLog(@"1 START viewDidLoad RootViewController");
self.title = @"Books";
// Set up the edit and add buttons.
self.navigationItem.leftBarButtonItem = self.editButtonItem;

NSLog(@"2 setup button viewDidLoad RootViewController");
// Configure the add button.
UIBarButtonItem *addButton = [[UIBarButtonItem alloc]   initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self   action:@selector(addBook)];
self.navigationItem.rightBarButtonItem = addButton;
[addButton release];  

NSLog(@"3 viewDidLoad RootViewController");
NSError *error;
// HERE IS THE CRASH SITE
 if (![[self fetchedResultsController] performFetch:&error]) {
  NSLog(@"Does not reach this point in viewDidLoad RootViewController");
  // Update to handle the error appropriately.
  NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
  abort();  // Fail
 }
 NSLog(@"END viewDidLoad RootViewController");
}

In the console I receive the following:

在控制台中，我收到以下信息：

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+entityForName: could not locate an NSManagedObjectModel for entity name 'Book''

I have read about this exception but I do not know the proper steps to resolve it.

我已阅读有关此异常的信息，但我不知道解决它的正确步骤。

回答by CraigH

Ok.

好的。

Placing the following code inside of the RootViewController's viewDidLoad eliminates the error:

将以下代码放在 RootViewController 的 viewDidLoad 中可以消除错误：

if (managedObjectContext == nil) 
{ 
    managedObjectContext = [(CoreDataBooksAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext]; 
    NSLog(@"After managedObjectContext: %@",  managedObjectContext);
}

I found someone with a similar problem here on SO: link text

我在 SO 上发现了一个有类似问题的人：链接文本

As Aryeh pointed out in that post: "In short you are trying to fetch an entity from an objectContext that hadn't been set up yet. Your options therefore are to set it up right then or do elsewhere in the app before this view loads."

正如 Aryeh 在该帖子中指出的那样：“简而言之，您正在尝试从尚未设置的 objectContext 中获取实体。因此，您的选择是立即设置它或在此视图加载之前在应用程序的其他地方进行设置.”

回答by Doug Richardson

In applicationDidFinishLaunching: you're doing the following:

在 applicationDidFinishLaunching: 您正在执行以下操作：

rootViewController.managedObjectContext = self.managedObjectContext;

But I don't see the code where self.managedObjectContext is setup. applicationDidFinishLaunching is called pretty early on. Are you sure you setup the managed object context?

但我没有看到设置 self.managedObjectContext 的代码。applicationDidFinishLaunching 很早就被调用了。您确定设置了托管对象上下文吗？

回答by Tim

Did you change the Core Data model at all? That error is common when the Core Data model for an app changes without also changing the underlying SQLite database, so the stored data and the model are out of sync.

你有没有改变核心数据模型？当应用程序的 Core Data 模型发生变化而不更改底层 SQLite 数据库时，该错误很常见，因此存储的数据和模型不同步。

Try completely removing your app from the Simulator or testing device, then reinstalling it and trying again.

尝试从模拟器或测试设备中完全删除您的应用，然后重新安装并重试。

回答by Luc Bloom

During my development, I could not find Entities that I added later on. What worked for me: (Basically a sanity-tip :-)

在我的开发过程中，我找不到后来添加的实体。什么对我有用：（基本上是一个理智的提示:-)

Uninstall the App EVERY TIME you change the Data Model!

每次更改数据模型时都卸载应用程序！

The Data Model is cached by Core Data between installs, to make sure the integrity stays in tact. Delete the App from the simulator / iPhone to be able to test your changes.

数据模型在安装之间由 Core Data 缓存，以确保完整性保持不变。从模拟器/iPhone 中删除应用程序，以便能够测试您的更改。

PS: does anyone know how to do that automatically?

PS：有谁知道如何自动做到这一点？