As we have seen so far in this book, application development using the Xamarin.Forms framework is executed on multiple domains. While the Xamarin.Forms layer creates a shared development domain that will be used to target native platforms, the target platforms can still be utilized for platform-specific implementation.
If we were to separate a Xamarin.Forms application into four quadrants by development strategy and application domain category, it will look like this:
In this setup, quadrant I (that is, the shared business logic) would represent the core logic implementation of the application. This domain will contain the view models, domain data descriptions, and service client implementation. Most importantly, the abstractions for platform-specific APIs (that is, the interfaces that will be implemented on the native platform) should be created in this domain so that each other domain, as well as the view models within this domain, can make use of them...