我想使用核心数据来持久化一些实体，例如事件。

因此我使用类 DSManagedObject 和 Event

DSManagedObject 类扩展了 NSManagedObject 并具有所有实体都可以使用的通用方法。 Event 类扩展 DSManagedObject。

下面的代码是DSManagedObject.h和.m。 .m 中的相关代码就是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 类中，我想调用 initWithEntity 但随后发生错误 [Event managedObjectModel] unrecognized selector sent to instance。 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，所以表现出理解；) 感谢帮助

PS:如果你想知道我为什么要重写init-method...复杂的原因^^

最佳答案

来自 Core Data文档:

In a typical Cocoa class, you usually override the designated initializer (often the init method). In a subclass of NSManagedObject, there are three different ways you can customize initialization —by overriding initWithEntity:insertIntoManagedObjectContext:, awakeFromInsert, or awakeFromFetch. You should not override init. You are discouraged from overriding initWithEntity:insertIntoManagedObjectContext: as state changes made in this method may not be properly integrated with undo and redo. The two other methods, awakeFromInsert and awakeFromFetch, allow you to differentiate between two different situations:

所以解决方案是覆盖 initWithEntity:insertIntoManagedObjectContext: 或利用 awakeFromInsert 或 awakeFromFecth。如果你想，ovveride 前者因为被称为之后 您调用 initWithEntity:insertIntoManagedObjectContext: 或 insertNewObjectForEntityForName:inManagedObjectContext:。

你有没有想要实现的特定目标？

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。您不能简单地通过发送 init 来初始化托管对象。 参见 NSManagedObject类以获取更多信息。

关于ios - 核心数据 - initWithEntity 导致无法识别的选择器发送到实例，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/11393363/