Implementing Dependent Components

We're picking up steam now. For this next section, we're not going to hold your hand quite as much when it comes to material we've already covered. Instead, we'll focus on the new stuff. Our new picker will display a list of US states in the left component and a list of ZIP codes in the right component that correspond to the state currently selected in the left.

We'll need a separate list of ZIP code values for each item in the left-hand component. We'll declare two arrays, one for each component, as we did last time. We'll also need an NSDictionary. In the dictionary, we're going to store an NSArray for each state (see Figure 7–20). Later, we'll implement a delegate method that will notify us when the picker's selection changes. If the value on the left changes, we will grab the correct array out of the dictionary and assign it to the array being used for the right-hand component. Don't worry if you didn't catch all that; we'll talk about it more as we get into the code.