In the previous chapter, we went full steam ahead with the development of the Messenger Android application. By doing so, we examined both Kotlin and Android application development in depth. We explored the Model-View-Presenter (MVP) pattern and how to use it to build powerful and fully functional Android applications. In addition to this, we covered the basics of Reactive programming and learned how to use RxJava and RxAndroid in our applications. We also learned about some of the available means by which we can communicate with a remote server. We learned about OkHttp and Retrofit, and then went one step further by implementing a fully functional Retrofit service to facilitate communication with the messenger API that we made in Chapter 4, Designing and Implementing the Messenger Backend with Spring Boot 2.0. Putting all this knowledge pertaining to Android and Kotlin together, we created both a login and signup user interface for the Messenger app.

In this chapter, we will finish the development of the Messenger app. In the process of doing so, we will cover the following topics:

• Working with application settings
• Working with ChatKit
• Android application testing
• Performing background tasks

Let's continue the development of our Messenger app by implementing the Main UI.