Question

我正在尝试设置通用模型，以便从后端检索数据并在我的iPhone应用程序中处理数据。我试图通过为所有类创建一个基类来实现这一目标，其中所有逻辑都定义为检索，保存和链接数据。最后一部分是我正在努力的部分。

在每个类中，我定义了对象名称（在Core Data中），如果某个对象与其他对象有关系，还有两个数组的对象名称数组（一个用于hasOne，一个用于hasMany）。

但是我似乎无法将检索到的对象转换为存储为字符串的某个类。这是我目前的代码：

/**
 Update the relationsships of an object which has relationsships from the type 'HasOne'.

 @param object
    Object from which the relations has to be updated.
 */
- (void)updateRelationshipsHasOne:(id)object {

    for(NSString *relation in self.hasOne) {        
        Class class = NSClassFromString(self.table);
        id anInstance = [class alloc];
        anInstance = object;        

        NSString *key = [[NSString alloc] initWithFormat:@"%@_id",[relation lowercaseString]];

        id delegata = [[UIApplication sharedApplication] delegate];
        NSManagedObjectContext *context = [delegata managedObjectContext];

        NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
        NSEntityDescription *entity = [NSEntityDescription
                                   entityForName:relation inManagedObjectContext:context];
        [fetchRequest setEntity:entity];

        NSPredicate *predicate = [NSPredicate predicateWithFormat: @"db_id == %i",[[object valueForKey:key] intValue]];
        [fetchRequest setPredicate:predicate];

        NSError *error;
        NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
        if(fetchedObjects && [fetchedObjects count] > 0) {
            id otherInstance = [fetchedObjects objectAtIndex:0];

            SEL s = NSSelectorFromString([[NSString alloc] initWithFormat:@"set%@",relation]);
            [anInstance performSelector:s withObject:otherInstance];
        }

    }

}

如果我将'anInstance'和'otherInstance'同时转换为所需的类，一切顺利。但是，整个目的是使方法通用，所以我需要一些方法来将两个变量都转换为存储为字符串的类。

非常感谢您提供任何帮助！

编辑：我收到的错误信息是：

2016-03-21 20:34:19.024 DeDamen[12303:834645] -[Heat setEvent]: unrecognized selector sent to instance 0x7fe2829d8cd0
2016-03-21 20:34:19.026 DeDamen[12303:834645] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[Heat setEvent]: unrecognized selector sent to instance 0x7fe2829d8cd0'
*** First throw call stack:
(
    0   CoreFoundation                      0x0000000109e68e65 __exceptionPreprocess + 165
    1   libobjc.A.dylib                     0x00000001094c0deb objc_exception_throw + 48
    2   CoreFoundation                      0x0000000109e7148d -[NSObject(NSObject) doesNotRecognizeSelector:] + 205
    3   CoreFoundation                      0x0000000109dbe90a ___forwarding___ + 970
    4   CoreFoundation                      0x0000000109dbe4b8 _CF_forwarding_prep_0 + 120
    5   *******                             0x0000000105d255ab -[CommonBase updateRelationshipsHasOne:] + 1627
    6   *******                             0x0000000105d24e60 -[CommonBase updateRelationships:] + 256
    7   *******                             0x0000000105d248a9 -[CommonBase save:handler:] + 1065
****
)
libc++abi.dylib: terminating with uncaught exception of type NSException

在这里，模型“Heat”指的是对象'anInstance'，而模型'Event'指的是对象'otherInstance'。关系是：一个热火有一个事件，一个事件有很多热量

创建通用Objective C关系模型

0 个答案: