Question

I have set up a Core Data model that includes an entity, Item with a 1->M relationship with the abstract entity Place, so that an item has many places. There are several entities with the parent set to Place.

I want to set up several UI elements depending on the descendent place types. I have a loop that looks something like this:

for (Place *place in item.places) {

}

… but I’m not sure how to detect what type the place is, and how to cast it to the proper type so that I can access its properties.

Thanks for any help!

Answer 1

Not entirely sure what you are asking, but sounds like you have a collection of objects which are of subclasses of Place, and you need to detect the concrete type at runtime.

Here’s how you do the branching and casting:

for (id object in item.places) {
    if ([object isKindOfClass:[SomeConcretePlace class]]) {
        ((SomeConcretePlace *)object).someProperty = something;

    } else if ([object isKindOfClass:[AnotherConcretePlace class]]) {
        somethingElse = ((AnotherConcretePlace *)object).someProperty;
    }
}

Be sure to look at docs for isKindOfClass: and isMemberOfClass: in NSObject reference to understand the difference, you can use either depending on the circumstances.

(You can substitute “id object” with “Place *object”, I was just using id in my code. — edit: or maybe you can’t if it’s abstract, see mzarra’s comment. “id” works fine.)