Question

I have three objects, Alien, Balloon, and Joystick all of which have a Location property, which I would like to observe from one controller.

when the controller observes a change in the Location variable of any of the objects, it updates the corresponding views’ center properties to the model’s location..

My problem is when I utilize the following function:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context

The parameter Object, which is of type id, is used to search for the correct index in my MutableArray of object models, and then with the corresponding index in my MutableArray of views, I change the center of the view..

However.. because the parameter is of type id, and not (Balloon *), (Joystick *), or (Alien *), xcode complains that Location is not a member of object in the following code:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    int index;

    if ([keyPath isEqualToString:@"Location"])
    {
        index = [balloons indexOfObjectIdenticalTo:object];

        [[balloonVs objectAtIndex:index] setCenter:CGPointMake(object.Location.x, object.Location.y)];
    }
}

I understand why it’s not working.. but don’t know how I could fix it.

Answer 1

You need to cast it to the right type. For instance, instead of :

object.location

…use:

((Balloon *)object).location