The job of the base classes and interfaces in our application framework are to encapsulate functionality that is commonly used by our View Models and Data Models. When the required functionality is more complex, or when it involves particular resources, or external connections, we implement it in separate service, or manager classes. For the remainder of this book, we will refer to these as manager classes. In larger applications, these are typically provided in a separate project.

Encapsulating them in a separate project enables us to reuse the functionality from these classes in our other applications. Which classes we use in this project will depend on the requirements of the application that we're building, but it will often include classes that provide the ability to send e-mails, to access the end user's hard drive, to export data in various formats, or to manage global application state for example.

We will investigate a number of these classes in this book, so that...