First experiments using MEF, MVVM and Silverlight 4 Beta

Note – this is a multi part post:

MEF (Managed Extensibility Framework) is a new library available in Silverlight 4 Beta which permits to build applications that can be incrementally extended in a declarative way using three simple concepts (read this post by Glenn Block for more infos):

  • Export an object;
  • Import it;
  • Compose it.

Mixing MEF and commanding, Silverlight has now a great support for structuring projects using a ViewModel approach, so I decided to use these new characteristics to build a simple solution.

Given an existing project, I added a ViewModel class implementing INotifyPropertyChanged:

    public class MainPageViewModel : ViewModelBase
        public MainPageViewModel()
            aViewModelProperty = "This is the content of a ViewModel property";

            aSampleCommand = new AViewCommand();

        public string aViewModelProperty { get; set; }

        public ICommand aSampleCommand {get; set;}

The problem I’ve solved using MEF is the binding of the DataContext property of the UserControl to a ViewModel class instance, so I’ve exported it using the MEF [Export] attribute.

The [Import] attribute and the PartInitializer.SatisfyImports(this);  are then used in the code behind of the xaml view in order to import and compose the ViewModel instance with the DataContext:

        public MainPage()

            this.DataContext = mainPageViewModel;

        public object mainPageViewModel { get; set; }

And this is the result:


As usually the source code is available for download here.

Happy Silverlighting!