Unrecognized selector sent to instance when calling NSManagedObject subclass self-made method

//Media+CoreDataClass.h
@interfaceMedia:NSManagedObject
    -(void) import:(NSArray*) received;
@end

@property(nullable, nonatomic, copy) NSSstring*id;
@property(nonatomic)int16_tdiskNo;
@property(nullable, nonatomic, copy) NSSstring* title;

// Media+CoreDataClass.m
-(void) import:(NSArray*) received {

    self.id = [received valueForKey: @"id" ];
    self.diskNo = [(NSNumber*) [received valueForKey:@"diskNo"] intValue];
    self.title = [received valueForKey: @"title";
}

appDelegate_=(AppDelegate*)[[UIApplication sharedApplication]delegate];
context_=appDelegate_.persistentContainer.viewContext;
Media*media=[NSEntityDescription insertNewObjectForEntityForName:@"Media"
                                             inManagedObjectContext:context_];
media.id=[json valueForKey:@"id"];
media.diskNo=[(NSNumber*)[json valueForKey:@"diskNo"]intValue];
media.title = [json valueForKey: @"title";
appDelegate_saveContext;

appDelegate_=(AppDelegate*)[[UIApplication sharedApplication]delegate];
context_=appDelegate_.persistentContainer.viewContext;
Media*media=[NSEntityDescription insertNewObjectForEntityForName:@"Media"
                                             inManagedObjectContext:context_];
media import:json;
appDelegate_saveContext;