Increment the value of a core-data model field

Question

I'm increasing the amount of a model field using the following code:

- (IBAction) counterButton: (id) sender {
    [model.amount++ stringValue];
}

It was working fine until I upgraded Xcode. Since then I've been getting the following error:

"Arithmetic on pointer to Interface 'NSNumber'. which is not a constant size in non-fragile ABI"

When the code was working it incremented the value by 1 each time a UIButton was touched.

any help would be greatly appreciated. thanks

Answer 1

You cant perform ++ on a NSNumber which in an object not a primitive type. Also it is an unmutable type.

If you want increase the value of amount you can try this:

- (IBAction) counterButton: (id) sender {
    NSInteger amount =[model.amount integerValue];
    amount++;
    model.amount = [NSNumber numberWithInteger:amount];

}

Answer 2

Unless model.amount used to be an NSInteger I don't see how that would ever have worked. The ++ operator doesn't work on NSNumbers. Or at least, it doesn't increment the value that's stored in it -- instead it would increment the pointer to the object, which isn't what you want.

Instead you need to increment the value "long hand."