Now that we can describe the various states that our UI is in, we can begin to apply the logic that is required to move between these states. We will use the Mediator pattern to accomplish this. The purpose of the Mediator pattern is to define how a set of objects interact with each other, and it does this by injecting an object in-between the ones that affect each other. This means that the objects in question do not actually communicate with each other, they work against an interface. This promotes loose coupling between objects.

There are essentially two parts to the Mediator pattern. The first part is to define an interface that the Mediator can call in order to apply the changes that it needs. The Mediator, in this case, is communicating with our UI classes. In our application, we will need the Mediator to be able to signal the UI to either show or hide...