Question

I have a simple iPhone app which accesses some remote data on start-up then asks the user to select one of the options chosen, but this happens each time the app starts, and I want the app to remember that choice for next time around, how can I persist this object using Core Data?

Im very new to Core Data, and I figure its something to do with adding an object to the NSManagedObjectContext but im not sure if there is a way to store one object against a key or something so that I can check if its been chosen before quickly to avoid doing the remote call…

EDIT

Ok, seems like NSUserDefaults is the way to go here, but I have a small issue, my custom class is extends NSManagedObject which I hear is a bit tough to store an instance of in NSUserDefaults, so I wrote a little converter that takes each property of the class and puts it in NSUserDefaults seperatly under different keys.

like so:

-(void)saveDeviceForUser:(Device*) device
{
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    NSData *encodedActive = [NSKeyedArchiver archivedDataWithRootObject:device.active];
    [defaults setObject:encodedActive forKey:@"UsersDevice_Active"];

    //and so on for each property of the Device object
}

then I retrieve my object in a similar fashion:

-(Device*)loadDeviceForUser
{
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

    NSData *encodedActive = [defaults objectForKey: @"UsersDevice_Active"];
    NSNumber* unarchivedActive = (NSNumber*)[NSKeyedUnarchiver unarchiveObjectWithData: encodedActive];

    Device *d = [[Device alloc] init];
    d.active = unarchivedActive;

    return d;
}

But, when I get to the line above of d.active = unarchivedActive I get an error:

Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘-[Device setActive:]: unrecognized selector sent to instance 0xac0be10’

My class properties are setup using @dynamic and not @synthesize, so do I have to implement the setters and getters in order for this to work? Will that upset Core Data in any way?

I hope that makes sense

Cheers,
Mark

Answer 1

I would store the object using NSUserDefaults

When storing a custom object, you must archive it correctly