+entityForName: nil 不是搜索实体名称“Account”的合法 NSManagedObjectContext 参数

我尝试了很多选择，但找不到解决这个问题的方法。我创建了一个核心数据文件并将实体命名为帐户，创建了一个名为用户名的字符串属性。然后将实体的类编辑为NSManagedObject，不确定这是否正确。现在，以下代码位于我的 LoginViewController 中：

- (void)viewDidLoad
{
    [super viewDidLoad];

    ITAppDelegate *appDelegate = (ITAppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = appDelegate.managedObjectContext;

    Account *newAccount = [NSEntityDescription insertNewObjectForEntityForName:@"Account" inManagedObjectContext:context];
    [newAccount setValue:@"Jorge" forKey:@"username"];
    [newAccount setPassword:@"password"];

    NSLog(@"username:%@   password: %@", [newAccount username], [newAccount password]);

}

我跟着本教程 http://josebolanos.wordpress.com/2012/03/16/core-data-passwords-in-keychain/我的代码文件如下所示：

ITAppDelegate.h

#import <UIKit/UIKit.h>

@interface ITAppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) UIWindow *window;

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

@end

ITAppDelegate.m

#import "ITAppDelegate.h"
#import "LoginViewController.h"

@implementation ITAppDelegate

@synthesize managedObjectContext = _managedObjectContext;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize managedObjectModel = _managedObjectModel;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary    *)launchOptions
{
    // Override point for customization after application launch.
    return YES;
}

#pragma mark - Core Data stack

- (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;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}


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

    return _persistentStoreCoordinator;
}

@end

帐户库.h

#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>

@interface AccountBase : NSManagedObject

@property (nonatomic, retain) NSString *username;


@end

帐户库.m

#import "AccountBase.h"

@implementation AccountBase

@dynamic username;

@end

帐户.h

#import "AccountBase.h"
#import <CoreData/CoreData.h>

@interface Account : AccountBase

@property (nonatomic, assign) NSString *password;

@end

帐户.m

#import "Account.h"
#import "KeychainHelper.h"

@implementation Account

- (NSString*)password
{
    if (self.username)
        return [KeychainHelper getPasswordForKey:self.username];
    return nil;
}

- (void)setPassword:(NSString*)aPassword
{
    if (self.username)
        [KeychainHelper setPassword:aPassword forKey:self.username];
}

- (void)prepareForDeletion
{
    if (self.username)
        [KeychainHelper removePasswordForKey:self.username];
}
@end

钥匙串助手.h

#import <Foundation/Foundation.h>

@interface KeychainHelper : NSObject

+ (NSString*)getPasswordForKey:(NSString*)aKey;
+ (void)setPassword:(NSString*)aPassword forKey:(NSString*)aKey;
+ (void)removePasswordForKey:(NSString*)aKey;

@end

钥匙串助手.m

#import "KeychainHelper.h"
#import <Security/Security.h>

@interface KeychainHelper ()
+ (NSMutableDictionary*)dictionaryForKey:(NSString*)aKey;
@end

@implementation KeychainHelper


static const NSString *ironTrainers = @"com.domain.myapplication";

+ (NSMutableDictionary*)dictionaryForKey:(NSString*)aKey
{
    NSData *encodedKey = [aKey dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableDictionary *searchDictionary = [NSMutableDictionary dictionary];

    [searchDictionary setObject:(__bridge id)kSecClassGenericPassword forKey:(__bridge id)kSecClass];
    [searchDictionary setObject:encodedKey forKey:(__bridge id)kSecAttrGeneric];
    [searchDictionary setObject:encodedKey forKey:(__bridge id)kSecAttrAccount];
    [searchDictionary setObject:ironTrainers forKey:(__bridge id)kSecAttrService];

    return searchDictionary;
}  

+ (NSString*)getPasswordForKey:(NSString*)aKey
{
    NSString *password = nil;

    NSMutableDictionary *searchDictionary = [self dictionaryForKey:aKey];
    [searchDictionary setObject:(__bridge id)kSecMatchLimitOne forKey:(__bridge id)kSecMatchLimit];
    [searchDictionary setObject:(id)kCFBooleanTrue forKey:(__bridge id)kSecReturnData];

    CFTypeRef result = NULL;
    BOOL statusCode = SecItemCopyMatching((__bridge CFDictionaryRef)searchDictionary, &result);
    if (statusCode == errSecSuccess) {
        NSData *resultData = CFBridgingRelease(result);
        password = [[NSString alloc] initWithData:resultData encoding:NSUTF8StringEncoding];
    }
    return (__bridge NSString *)(result);
}

+ (void)removePasswordForKey:(NSString*)aKey
{
    NSMutableDictionary *keyDictionary = [self dictionaryForKey:aKey];
    SecItemDelete((__bridge CFDictionaryRef)keyDictionary);
 }

+ (void)setPassword:(NSString*)aPassword forKey:(NSString*)aKey
{
    [KeychainHelper removePasswordForKey:aKey];

    NSData *encodedPassword = [aPassword dataUsingEncoding:NSUTF8StringEncoding];

    NSMutableDictionary *keyDictionary = [self dictionaryForKey:aKey];
    [keyDictionary setObject:encodedPassword forKey:(__bridge id)kSecValueData];
    SecItemAdd((__bridge CFDictionaryRef)keyDictionary, nil);
}

@end

任何帮助表示赞赏。谢谢。

- (NSManagedObjectContext *)managedObjectContext
{
    if (managedObjectContext != nil) return managedObjectContext;

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {

        managedObjectContext = [[NSManagedObjectContext alloc] init];
        [managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return managedObjectContext;
}

• 您还没有提供延迟加载的实现persistentStoreCoordinator
• so coordinator一直会nil
• 所以你总会回来nil从这个方法
• 这意味着您将始终收到上述错误。

解释一下这个错误：

+entityForName: nil 不是搜索实体名称“Account”的合法 NSManagedObjectContext 参数

阅读它并不能立即明显看出，但这意味着nil不是为托管对象上下文传递的合法内容。第一次阅读时，看起来你正在做entityForName:nil但事实并非如此。

要解决此问题，您需要提供有效的持久性存储协调器。我有一篇小文章here http://commandshift.co.uk/blog/2013/09/07/the-core-data-stack/这解释了您需要多少代码来设置核心数据堆栈，这可能会对您有所帮助。