Question

I’m diving into iOS development and I have a few questions about manipulating a simple Core Data object that I created in Xcode. After using the object editor, here’s the class that Xcode generated for me…

@interface Alarm :  NSManagedObject  
{
}

@property (nonatomic, retain) NSNumber * Enabled;
@property (nonatomic, retain) NSString * Label;
@property (nonatomic, retain) NSNumber * Snooze;

@end

@implementation Alarm 

@dynamic Enabled;
@dynamic Label;
@dynamic Snooze;

@end

Here’s a code snipped where I try and create an Alarm object that I plan to add to my ManagedObjectContext…

- (void)saveAlarm:(id)sender {

    Alarm *alarm = [[Alarm alloc] init];

    alarm.Label = [NSString stringWithString:txtLabel.text];    
    alarm.Snooze = [NSNumber numberWithBool:switchSnooze.on];
    alarm.Enabled = [NSNumber numberWithBool:YES];

    [addAlarmDelegate insertNewAlarm:alarm];
    [alarm release]; 
}

My code crashes the first time I try and assign a value to one of the properties of alarm, on the line…

alarm.Label = [NSString stringWithString:txtLabel.text];

with the following crash message in the console…

reason: '-[Alarm setLabel:]: unrecognized selector sent to instance 0x5e33640

what am I missing here?

Thanks so much in advance for your help!

Answer 1

You should not allocate and init an NSManagedObject-based object directly. You should use

[NSEntityDescription insertNewObjectForEntityForName:@"Alarm" inManagedObjectContext:moc];

It might be the reason for it not to work. Because it is usually pretty straight forward to make it work.

The documentation says:

If you instantiate a managed object
directly, you must call the designated
initializer
(initWithEntity:insertIntoManagedObjectContext:).

And in initWithEntity:insertIntoManagedObjectContext:’s documentation:

Important: This method is the
designated initializer for
NSManagedObject. You must not
initialize a managed object simply by
sending it init.