In this chapter, we went over the concept for a sample application that we will be building throughout this book called XamChat. We also implemented the core business objects for the application in the Model layer. Since we do not have a server to support this application yet, we implemented a fake web service. This gives us the flexibility to move forward with the app without building a server application. We also implemented the ViewModel layer. This layer will expose operations in a simple way to the View layer. Finally, we wrote tests covering the code we've written so far using NUnit. Writing tests against shared code in a cross-platform application can be very important, as it is the backbone of more than one application.

After reading this chapter, you should have completed the shared library for our cross-platform application in its entirety. You should have a very firm grasp on our application's architecture and its distinct Model and ViewModel layers. You should also have a good understanding on how to write fake versions of parts of your application that you may not be ready to implement quite yet. In the next chapter, we will implement the iOS version of XamChat.