A year ago, when the majority of the current Android team started working at upday, the application was far from being the robust, stable app that we wanted it to be. We tried to understand why our code was in such bad shape and we found two main culprits: continuous changing of the UI and the lack of an architecture that supported the flexibility that we needed. The app was already at its fourth redesign in six months. The design pattern chosen seemed to be Model-View-Controller but was then already a “mutant”, far from how it should be. Let’s discover together what the Model-View-Controller pattern is; how it has been applied in Android over the years; how it should be applied so it can maximize testability; and some of its advantages and disadvantages. The Model-View-Controller Pattern In a world where the user interface logic tends to change more often than the business logic, the desktop and Web developers needed a way of separating user interface functionality. The MV