OK, things are looking pretty good. We’ve got our first bit of visuals coming through, but so far this is just an inert view with no behavior. We just have some data in the view, and we construct the view hierarchy to display it.

Things start to get more interesting once we layer on behavior in an application. The first bit of behavior we will concentrate on is navigation. We need to be able to bring up sheets, drill down to screens, and show alerts. And you may think those 3 things sound quite different, but we will show that they can be modeled in the same way.

And as soon as we start navigating around to different screens, things start getting a lot more complicated. We need to start thinking about how to best model our domains, and we need to think about how parent and child domains can communicate with each other.