核心数据和UITabBar控制器 - 帮助？ [英] Core Data and UITabBar Controller - help?

问题描述

所以我有一个项目与UITabBarController和一些导航控制器，我试图实现Core Data。它只是不工作。

我有一些奇怪的设置：
UITabBarController - >导航控制器 - >表视图控制器

我已经复制了所有的核心数据代码，并添加了一个具有属性（'Event'和'name' - 与教程一样）的实体。我不断收到错误：
由于未捕获异常NSInternalInconsistencyException导致应用程序失败，原因：'+ entityForName：找不到实体名称Event的NSManagedObjectModel

错误只发生在我切换到表视图，我想填充Core Data内容。

我发现错误发生在表中的这一行View Controller：

NSEntityDescription * entity = [NSEntityDescription entityForName：@EventinManagedObjectContext：managedObjectContext]; p>

这似乎与此对应（在应用程序代表中）：

  NSManagedObjectContext * context = [self managedObjectContext]; 
 
 if（！context）{
 
 //处理错误。 
  

NSLog（@\\\
不能为自己创建*上下文）;

 } 
 
 rootViewController.managedObjectContext = context; 
  

任何帮助？

更新：我设法使其工作（非常令人兴奋的时刻，斯坦福赢得了一半 - 好日子）。我现在引用它从应用程序代表。 ）

解决方案

您的管理对象上下文可能未设置，实体事件显然不是对于nil上下文有效。

我在所有视图控制器中使用对我的应用程序委托的引用，以便他们可以访问一个托管对象上下文。听起来像其他人经常使用单例管理Core Data，并从中获取管理对象上下文。

UPDATE

在在Cocoa / Cocoa Touch应用程序中放置Core Data Stack的位置。

下面是一些用于在应用委托中保留Core Data堆栈的示例代码：

使用Apple的标准Core在YourAppDelegate中实现数据堆栈。 managedObjectContext实现为一个示例，但managedObjectModel和persistentStoreCoordinator也必须实现。

YourAppDelegate.h ：

  @interface YourAppDelegate：NSObject< UIApplicationDelegate> {
 // Core Data stuff 
 NSManagedObjectModel * managedObjectModel; 
 NSManagedObjectContext * managedObjectContext; 
 NSPersistentStoreCoordinator * persistentStoreCoordinator; 
 
 //其他应用程式ivars 
} 
  

YourAppDelegate.m ：

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

在每个视图控制器中，获取对应用代理的引用，根据需要获取managedObjectContext。例如，当设置fetchedResultsController;

RootViewController.h ：

  @interface RootViewController：UITableViewController< NSFetchedResultsControllerDelegate> {
 NSFetchedResultsController * fetchedResultsController; 
 
 YourAppDelegate * app; 
} 
  

RootViewController.m ：

  #importRootViewController.h
 #importYourAppDelegate.h
 
 @implementation RootViewController 
 
 @synthesize fetchedResultsController; 
 
  - （void）viewDidLoad {
 [super viewDidLoad]; 
 
 app =（YourAppDelegate *）[UIApplication sharedApplication] .delegate; 
} 
 
  - （NSFetchedResultsController *）fetchedResultsController {
 if（fetchedResultsController！= nil）{
 return fetchedResultsController; 
} 
 
 NSFetchRequest * fetchRequest = [[NSFetchRequest alloc] init]; 
 NSEntityDescription * entity = [NSEntityDescription entityForName：@EventinManagedObjectContext：app.managedObjectContext]; 
 [fetchRequest setEntity：entity]; 
 
 //设置批处理大小，谓词和&排序键等
 
 NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest managedObjectContext：app.managedObjectContext sectionNameKeyPath：nil cacheName：@Root]; 
 aFetchedResultsController.delegate = self; 
 self.fetchedResultsController = aFetchedResultsController; 
 
 [aFetchedResultsController release]; 
 [fetchRequest release]; 
 
 return fetchedResultsController; 
} 
  

So I have a Project with a UITabBarController and a few Navigation Controllers, and I am trying to implement Core Data. Its just not working.

I have a bit of a weird setup: UITabBarController -> Navigation Controller -> Table View Controller

I have copied all of the Core Data code and added an entity with an attribute ('Event' and 'name' - just like the tutorials). I keep getting the error: erminating app due to uncaught exception 'NSInternalInconsistencyException', reason: '+entityForName: could not locate an NSManagedObjectModel for entity name 'Event''

The error only occurs when I switch to the Table View I want populated by the Core Data content.

I found that the error occurs on this line in the Table View Controller:

NSEntityDescription *entity = [NSEntityDescription entityForName:@"Event" inManagedObjectContext:managedObjectContext];

This seems to correspond with this (in the App Delegate):

NSManagedObjectContext *context = [self managedObjectContext];

if (!context) {

    // Handle the error.

NSLog(@"\nCould not create *context for self");

}

rootViewController.managedObjectContext = context;

Any Help?

Update: I managed to get it working (very exciting moment, and Stanford is winning at the half - so far its a good day). I am now referencing it from the App Delegate. Ahhh, this feels soo good :)

解决方案

Your managed object context is probably not set and the entity "Event" is obviously not valid for a nil context.

I use a reference to my app delegate in all my view controllers so they can access the one managed object context. It sounds like others often use a singleton to manage Core Data and would get the managed object context from that.

UPDATE

There is a good discussion about where to keep the Core Data stack in Where to place the "Core Data Stack" in a Cocoa/Cocoa Touch application.

Here is some example code for keeping the Core Data stack in the app delegate:

Use Apple's standard Core Data stack implementation in YourAppDelegate. managedObjectContext is implemented as an example, but managedObjectModel and persistentStoreCoordinator must be implemented as well.

YourAppDelegate.h:

@interface YourAppDelegate : NSObject <UIApplicationDelegate> {
    // Core Data stuff
    NSManagedObjectModel *managedObjectModel;
    NSManagedObjectContext *managedObjectContext;       
    NSPersistentStoreCoordinator *persistentStoreCoordinator;

    // other app ivars
}

YourAppDelegate.m:

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

In every view controller, get a reference to the app delegate and use it to get the managedObjectContext as needed. For example, when setting up the fetchedResultsController;

RootViewController.h:

@interface RootViewController : UITableViewController <NSFetchedResultsControllerDelegate> {
    NSFetchedResultsController *fetchedResultsController;

    YourAppDelegate *app;
}

RootViewController.m:

#import "RootViewController.h"
#import "YourAppDelegate.h"

@implementation RootViewController

@synthesize fetchedResultsController;

- (void)viewDidLoad {
    [super viewDidLoad];

    app = (YourAppDelegate*)[UIApplication sharedApplication].delegate;
}

- (NSFetchedResultsController *)fetchedResultsController {
    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }

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

    // setup the batch size, predicate, & sort keys, etc

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

    [aFetchedResultsController release];
    [fetchRequest release];

    return fetchedResultsController;
}    

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