核心数据 - initWithEntity导致无法识别的选择器发送到实例

Question

我想使用核心数据来保存某些实体,比如事件.

因此我使用类DSManagedObject和Event

该类DSManagedObject扩展NSManagedObject并具有所有实体可以使用的一般方法.课程Event延伸DSManagedObject.

以下代码是DSManagedObject.h和.m.这里的相关代码.m只是getContext- 方法.

@interface DSManagedObject : NSManagedObject

+ (NSManagedObjectContext *)getContext;
- (NSArray*)getEntitiesForName:(NSString*)_entityName context:(NSManagedObjectContext*)_context;
- (Event*)getEntityForName:(NSString*)_entityName forEventId:(NSInteger)_eventId context:(NSManagedObjectContext*)_context;
- (bool)deleteEntityForName:(NSString*)_entityName forEventId:(NSInteger)_eventId context:(NSManagedObjectContext*)_context;

@end


@implementation DSManagedObject

+ (NSManagedObjectContext *)getContext {

    NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES],NSMigratePersistentStoresAutomaticallyOption,
                             [NSNumber numberWithBool:YES],
                             NSInferMappingModelAutomaticallyOption, nil];


    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;
    NSURL *storeUrl = [NSURL fileURLWithPath:[basePath stringByAppendingFormat:@"DesertStorm.sqlite"]];
    NSPersistentStoreCoordinator *persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[NSManagedObjectModel mergedModelFromBundles:nil]];
    NSError *error = nil;

    if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:options error:&error]) {
        NSLog(@"error loading persistent store..");
        [[NSFileManager defaultManager] removeItemAtPath:storeUrl.path error:nil];
        if (![persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeUrl options:options error:&error]) {
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }



    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
    [context setPersistentStoreCoordinator:persistentStoreCoordinator];

    return context;


}

现在在Event我要调用的类中initWithEntity,然后[Event managedObjectModel] unrecognized selector sent to instance发生错误.什么原因 ？:(

@interface Event : DSManagedObject

@property (assign)              NSInteger   eventId;

@end


@implementation Event

@dynamic eventId;

- (id)init {

    NSEntityDescription *entity = [NSEntityDescription insertNewObjectForEntityForName:@"Event" inManagedObjectContext:[DSManagedObject getContext]];
    self = [self initWithEntity:entity insertIntoManagedObjectContext:[DSManagedObject getContext]];  // error occurs
    self = [super init];
    if (self) {

    }
    return self;
}

...

@end

我是使用核心数据的新手,所以表示理解;)感谢您的帮助

PS:如果你想知道我为什么要覆盖init-method ...复杂的原因^^

Answer 1

来自Core Data doc:

在典型的Cocoa类中,通常会覆盖指定的初始化程序(通常是init方法).在NSManagedObject的子类中,有三种不同的方法可以自定义初始化 - 通过覆盖initWithEntity:insertIntoManagedObjectContext:,awakeFromInsert或awakeFromFetch.你不应该覆盖init.不鼓励您覆盖initWithEntity:insertIntoManagedObjectContext:由于此方法中所做的状态更改可能无法与undo和redo正确集成.另外两个方法awakeFromInsert和awakeFromFetch允许您区分两种不同的情况:

所以灵魂是覆盖initWithEntity:insertIntoManagedObjectContext:或利用awakeFromInsert或awakeFromFecth.如果你想,ovveride前者由于调用后调用initWithEntity:insertIntoManagedObjectContext:或insertNewObjectForEntityForName:inManagedObjectContext:.

你想实现一个特定的目标吗？

编辑

尝试覆盖initWithEntity:insertIntoManagedObjectContext:而不是init

- (id)initWithEntity:(NSEntityDescription*)entity insertIntoManagedObjectContext:(NSManagedObjectContext*)context    
{    
    self = [super initWithEntity:entity insertIntoManagedObjectContext:context];
    if (self != nil) {

        // Perform additional initialization.

    }

    return self;    
}

该方法是NSManagedObject的指定初始化程序.您不能仅通过发送init来初始化托管对象.有关NSManagedObject详细信息,请参阅课程