While we were busy thinking through the interaction design elements of new IMSA mobile apps, we knew we were going to have to build six apps (iOS, Android, Universal Apps for phone and tablet). The app architecture we chose to follow for this is Model-View-ViewModel (or MVVM). Our mission was to maximize the amount of code sharing across all implementations of the app. The more code sharing we could do, the less code we would have to develop for each platform. Less code means less time to develop and less to test, making the aggressive schedule more achievable.
The Model layer contains the business logic and data that will drive the IMSA app. Data would be served through a scalable cloud infrastructure being constructed for the mobile apps. Regardless of mobile OS, the business logic and data will remain the same. How we access the data in the cloud and retrieve would also remain the same. These layers are devoid of any user interface elements are a logical candidate for re-use across all the mobile operating systems. Perfect – one layer to write one. But we want more.
We were suspicious that the View layer would be so unique across mobile operating systems that the ViewModel layer would not be re-usable. The ViewModel layer is responsible for binding the Model layer (the business logic) to a View (the user interface). Remember we are talking about code sharing across iOS, Android, and Universal Apps – this have to be do so different that writing a consistent and shareable ViewModel layer would not be possible – right? Wrong! After some initial prototyping we were pleasantly surprised. The path we have chosen is going to allow us to use the same code in the ViewModel layer across all operating systems.
From our early calculations, thanks to Visual Studio and Xamarin, we are predicting to see about 75% code re-use (of the non-generated code) across all the implementations! Excellent news for the developers and project manager. We’ll dive into code examples in an upcoming blog, but next we’ll discuss our approach with Azure. Also, this video has additional information for code re-use with Xamarin.