View controllers are glue-like components that hold an app together. They are responsible for moderating between the model and the view layer. As the moderator, they are highly-specialized according to the needs of the module they belong to. As a result, the controller layer is often the part that is not reusable in other parts of the app or in other apps.

As the controller is responsible for many different tasks, it often tends to become big. It is a good practice to construct the controller layer of one specific feature out of different controller classes. For instance, beginners often put their networking code into the same class that is responsible for filling the UI with information. This results in a so-called "god" class, a class that knows and controls everything.

Such classes are hard to write, read, and maintain and should, therefore, be avoided. To make the View Controller showing the list of items clean, we will separate the data source...