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我正在研究我的文憑項目，其中包括iOS客戶端與核心數據數據庫和Ruby on Rails服務器。我正在使用RestKit進行它們之間的通信。目前，我有一個大問題，讓整個系統的工作：當我嘗試映射到從服務器對象的響應，我得到以下異常：RestKit崩潰，因爲NSManagedObjectContext是零在RKResponseMapperOperation
2013-02-08 22:40:43.947 App[66735:5903] *** Assertion failure in -[RKManagedObjectResponseMapperOperation performMappingWithObject:error:], ~/Repositories/App/RestKit/Code/Network/RKResponseMapperOperation.m:358
2013-02-08 23:04:30.562 App[66735:5903] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Unable to perform mapping: No `managedObjectContext` assigned. (Mapping response.URL = http://localhost:3000/contacts?auth_token=s78UFMq8mCQrr12GZcyx)'
*** First throw call stack:
(0x1de9012 0x1c0ee7e 0x1de8e78 0x16a4f35 0x8f56e 0x8d520 0x1647d23 0x1647a34 0x16d4301 0x23a253f 0x23b4014 0x23a52e8 0x23a5450 0x90ac6e12 0x90aaecca)
libc++abi.dylib: terminate called throwing an exception
我試圖加載來自服務器的聯繫人列表（一個數組），應該將其保存爲核心數據中的「用戶」。
我在數據模型類中構建了我所有的核心數據代碼，就像我在本視頻中看到的：http://nsscreencast.com/episodes/11-core-data-basics。那就是：
頭文件
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
@interface AppDataModel : NSObject
+ (id)sharedDataModel;
@property (nonatomic, readonly) NSManagedObjectContext *mainContext;
@property (nonatomic, strong) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;
- (NSString *)modelName;
- (NSString *)pathToModel;
- (NSString *)storeFilename;
- (NSString *)pathToLocalStore;
@end
實現文件：
#import "AppDataModel.h"
@interface AppDataModel()
- (NSString *)documentsDirectory;
@end
@implementation AppDataModel
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
@synthesize mainContext = _mainContext;
+ (id)sharedDataModel {
static AppDataModel *__instance = nil;
if (__instance == nil) {
__instance = [[AppDataModel alloc] init];
}
return __instance;
}
- (NSString *)modelName {
return @"AppModels";
}
- (NSString *)pathToModel {
return [[NSBundle mainBundle] pathForResource:[self modelName]
ofType:@"momd"];
}
- (NSString *)storeFilename {
return [[self modelName] stringByAppendingPathExtension:@"sqlite"];
}
- (NSString *)pathToLocalStore {
return [[self documentsDirectory] stringByAppendingPathComponent:[self storeFilename]];
}
- (NSString *)documentsDirectory {
NSString *documentsDirectory = nil;
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
documentsDirectory = [paths objectAtIndex:0];
return documentsDirectory;
}
- (NSManagedObjectContext *)mainContext {
if (_mainContext == nil) {
_mainContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
_mainContext.persistentStoreCoordinator = [self persistentStoreCoordinator];
}
return _mainContext;
}
- (NSManagedObjectModel *)managedObjectModel {
if (_managedObjectModel == nil) {
NSURL *storeURL = [NSURL fileURLWithPath:[self pathToModel]];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:storeURL];
}
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
if (_persistentStoreCoordinator == nil) {
NSLog(@"SQLITE STORE PATH: %@", [self pathToLocalStore]);
NSURL *storeURL = [NSURL fileURLWithPath:[self pathToLocalStore]];
NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc]
initWithManagedObjectModel:[self managedObjectModel]];
NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption,
[NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];
NSError *e = nil;
if (![psc addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil
URL:storeURL
options:options
error:&e]) {
NSDictionary *userInfo = [NSDictionary dictionaryWithObject:e forKey:NSUnderlyingErrorKey];
NSString *reason = @"Could not create persistent store.";
NSException *exc = [NSException exceptionWithName:NSInternalInconsistencyException
reason:reason
userInfo:userInfo];
@throw exc;
}
_persistentStoreCoordinator = psc;
}
return _persistentStoreCoordinator;
}
@end
的User類是非常簡單的，自動生成和Xcode。
頭文件
#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>
@interface User : NSManagedObject
@property (nonatomic, retain) NSString * email;
@property (nonatomic, retain) NSString * firstName;
@property (nonatomic, retain) NSString * lastName;
@property (nonatomic, retain) NSNumber * userID;
@end
實現文件：
#import "User.h"
@implementation User
@dynamic email;
@dynamic firstName;
@dynamic lastName;
@dynamic userID;
@end
就像數據模型類，我有一個服務器管理器類我使用的通信：
頁眉file：
#import <Foundation/Foundation.h>
#import <RestKit/RestKit.h>
#import "AppServerProtocol.h"
#import "AppDataModel.h"
@interface AppServer : NSObject <AppServerDelegate>
+ (id)sharedInstance;
@property (strong, nonatomic) RKObjectManager *objectManager;
@property (strong, nonatomic) RKEntityMapping *userMapping;
@end
而且實現文件：
#import "AppServer.h"
#import "User.h"
#import "Device.h"
#import "Ping.h"
#import "AppAppDelegate.h"
@interface AppServer()
@property BOOL initialized;
@end
@implementation AppServer
+ (id)sharedInstance {
static AppServer *__instance = nil;
if (__instance == nil) {
__instance = [[AppServer alloc] init];
__instance.initialized = NO;
}
if (![__instance initialized]) {
[__instance initServer];
}
return __instance;
}
- (void)initServer {
// initialize RestKit
NSURL *baseURL = [NSURL URLWithString:@"http://localhost:3000"];
_objectManager = [RKObjectManager managerWithBaseURL:baseURL];
// enable activity indicator spinner
[AFNetworkActivityIndicatorManager sharedManager].enabled = YES;
// initialize managed object store
_objectManager.managedObjectStore = [[RKManagedObjectStore alloc] initWithManagedObjectModel:[[AppDataModel sharedDataModel] managedObjectModel]];
_userMapping = [RKEntityMapping mappingForEntityForName:@"User" inManagedObjectStore:_objectManager.managedObjectStore];
[_userMapping addAttributeMappingsFromDictionary:@{
@"email" : @"email",
@"firstName" : @"first_name",
@"lastName" : @"last_name"
}];
[_userMapping setIdentificationAttributes: @[@"userID"]];
RKResponseDescriptor *contactsResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:_userMapping pathPattern:@"/contacts" keyPath:nil statusCodes:nil];
[_objectManager addResponseDescriptor:contactsResponseDescriptor];
_initialized = YES;
}
// contacts
- (void)getContactsForCurrentUser {
NSString *authToken = [[NSUserDefaults standardUserDefaults] objectForKey:@"AppAuthenticationToken"];
[_objectManager getObjectsAtPath:@"/contacts" parameters:@{@"auth_token": authToken} success:^(RKObjectRequestOperation *operation, RKMappingResult *mappingResult) {
RKLogInfo(@"Load collection of contacts: %@", mappingResult.array);
} failure:^(RKObjectRequestOperation *operation, NSError *error) {
RKLogError(@"Operation failed with error: %@", error);
}];
}
@end
所以，當我打開聯繫人表視圖，它設置正確使用已取得的成果控制器（成功拉動實體走出DB），我有一個危險的刷新按鈕，它調用你剛纔上面閱讀方法：
- (void)downloadContacts {
[[AppServer sharedInstance] getContactsForCurrentUser];
}
這裏是響應格式：
[
{
"created_at":"2013-01-11T14:03:57Z",
"email":"[email protected]",
"first_name":"John",
"id":2,
"last_name":"Doe",
"updated_at":"2013-02-07T10:57:16Z"
},
{
"created_at":"2013-01-11T14:03:57Z",
"email":"[email protected]",
"first_name":"Jane",
"id":3,
"last_name":"Doe",
"updated_at":"2013-02-07T10:57:16Z"
}
]
和異常控制檯前狀態如下：
2013-02-08 22:40:36.892 App[66735:c07] I restkit:RKLog.m:34 RestKit logging initialized...
2013-02-08 22:40:36.994 App[66735:c07] SQLITE STORE PATH: ~/Library/Application Support/iPhone Simulator/6.0/Applications/D735548F-DF42-4E13-A7EF-53DF0C5D8F3B/Documents/AppModels.sqlite
2013-02-08 22:40:37.001 App[66735:c07] Context is ready!
2013-02-08 22:40:43.920 App[66735:c07] I restkit.network:RKHTTPRequestOperation.m:154 GET 'http://localhost:3000/contacts?auth_token=s78UFMq8mCQrr12GZcyx'
2013-02-08 22:40:43.945 App[66735:c07] I restkit.network:RKHTTPRequestOperation.m:181
的RestKit庫的線，被拋出整個異常之前失敗的：
NSAssert(self.managedObjectContext, @"Unable to perform mapping: No `managedObjectContext` assigned. (Mapping response.URL = %@)", self.response.URL);
我已經跟着回到AppServer中的initServer方法。米文件，在其中，該方法返回前，RKObjectManager類的的性質是這樣的：http://imgur.com/LM5ZU9m
正如我所調試，我已經跟蹤的問題是無法與服務器側或所述通信該應用程序 - 我可以看到JSON接收並反序列化到一個數組中，但是當它傳遞給下一個應該將其保存到Core Data的方法時，整個應用程序將由於受管對象上下文的NSAssert而進入kaboom。
任何幫助非常感謝！