Question

I have an app that uses CoreData. I created NSManagedObjects for the two object types in CoreData. When I try to use the object and set a property on the object the compiler says “[User setUsername:]: unrecognized selector sent to instance”. It doesn’t matter what attribute I, [User setValue], try it always gives unrecognized?

User *joeBlow = [[User alloc] init];
[joeBlow setUsername:@"joeblow"];

OR
User *joeBlow = [[User alloc] init];
joeBlow.username = @”JoeBlow”;

both give “unrecognized selector sent to instance”

Below is my code for USER:

User.h

@interface User : NSManagedObject

  @property (nonatomic, retain) NSString * address1;
  @property (nonatomic, retain) NSString * username;
  @property (nonatomic, retain) NSString * zip;
  @property (nonatomic, retain) NSString * email;

@end

User.m

@implementation User

  @dynamic address1;
  @dynamic username;
  @dynamic zip;
  @dynamic email;

@end

Answer 1

You can’t create new instances of Core Data entities by the normal alloc–init pattern (unlike other classes). Instead, call a class method on NSEntityDescription:

User *joeBlow = [NSEntityDescription 
                 insertNewObjectForEntityForName:@"User"
                 inManagedObjectContext:self.managedObjectContext];
[joeBlow setUsername:@"joeblow"];

See Apple’s Core Data Programming Guide for more information.

Finally, note that [jb setUsername:@"jb"] and jb.username = @"jb" are the same – the latter is dot notation, a different way of expressing the former.