Let's break down the major views that will make up the main screen of the application:

1: header view, 2: thread view, 3: message view, and 4: composer view; main view encompasses views 1 - 4

The login view is the simplest; a self-contained view, view controller, and a view model to bind with the values of the login form. It's not shown in the preceding mockup because it's the only one on the screen at the time, almost standalone.

There's a caveat to this. For the first time, we'll be using an over-arching controller to deal with the interactions between views. In the previous chapter, this was left to the "main" view controller, since the "main" view was the container for every part of our application. Here, the login view and the rest of the application are effectively independent from each other and so it makes sense to have a "third party" helping them to work together.

We'll call this top-level controller our "root" controller. It's not a view controller, but a completely...