This makes your code easier to test and helps you follow the DRY principle : 'Don't Repeat Yourself.' By removing all the calls to create new instances of the dependencies we need, we are in effect reducing redundancy in our code. All the tedious ceremony of creating these objects is now the responsibility of the DI container. You are coding to a contract instead of to an implementation. The beauty of DI is that you are making your code less coupled to other classes. You can inject all of the dependent services in your ViewModel, and use them as if you had created them in your own class. When using a dependency injection (DI) container in your application, MVVM can also be very beneficial to you. For example, one view would be a read-only screen, and the other would be an edit screen. This means that we could have two views implemented and use the same ViewModel class. Another advantage to this model is the ability to reuse our ViewModels across Views. It is a lot easier to write mock tests when we don't have to re-create the user interface, and all we are concerned with are the business rules. Perhaps the biggest benefit for using this model is testing. Because of this declarative programming model and the rich data-binding that is inherent in XAML, we can easily put our code in a ViewModel class instead of the code-behind for the user control. This helps facilitate better separation of the user interface and the code that reacts to the user interface. Silverlight shares the same power of Windows Presentation Foundation ( WPF) and gives us a rich declarative user interface programming model.

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