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PrismHelper.PrepareWithoutBootstrapper();

PrismHelper.InitializeMainWindow();

The latest version of the guidance, Prism, includes a feature named "User Interface Composition". Basically it allows build a mosaic like application by loading multiple views that comes from different modules into an active regions exposed by a control, also know as the shell.

But all this is about view models. Therefore, the Catel team decide to introduce an extension that implements a good starting point in order create a composite user interface without actually referencing any view. At this point, you must have heared about of the UIVisualizerService, and the way it can resolve a view from an instance of a view model. So, we are please to introduce you the UICompositionService.

Making the region manager available

First of all, you must make available the region manager on the instance of ServiceLocator. A Prism based application uses MEF or Unity as primary IoC contanier. Therefore, you must synchronize this container with the Catel one, overriding the ConfigureContainer method of the application Bootstrapper class, using the following code:

protected override void ConfigureContainer()
{
    base.ConfigureContainer();

    if (ServiceLocator.Instance.IsExternalContainerSupported(this.Container))
    {
        ServiceLocator.Instance.RegisterExternalContainer(this.Container);
    }
}

but if you use ServiceLocator primary IoC contanier, and your Bootstrapper class inherits from BootstrapperBase the region manager is actually available and you don't have to write the synchronization container code.

Activating a view into a specific region

To activate a view into a specific region, use the following code:

var viewModel = new EmployeeViewModel();

var dependencyResolver = this.GetDependencyResolver();
var uiCompositionService = dependencyResolver.Resolve<IUICompositionService>();
uiCompositionService.Activate(viewModel, "MainRegion");

But if the context allows you to know the instance of the view model of the view owner of the region where you will inject a view, is strongly recommended use the Activate overload that allows you to specify the parent view-model. This call will enforce the view models parent-child relationship:

uiCompositionService.Activate(viewModel, this, "MainRegion");

Dealing with more than one and only one shell

Actually you are able to inject views (referencing it's view models) in any window. Just like the previous example but in combination with the experimental extension method Show:

var dependencyResolver = this.GetDependencyResolver();
var uiVisualizerService = dependencyResolver.Resolve<IUIVisualizerService>();

var uiCompositionService = dependencyResolver.Resolve<IUICompositionService>()
var windowViewModel = new WindowWithRegionViewModel();

uiVisualizerService.Show(windowViewModel, () => { uiCompositionService.Activate(new EmployeeViewModel(), windowViewModel, "WindowMainRegion") });

Deactivating a view

To deactivate a view, use the following code:

uiCompositionService.Deactivate(viewModel);

 If you keep your view model alive (see: Keeping view models alive), you can reactivate a deactivated the view using Activate method without specify the region name.

Deactivating a view automatically

If you close the view model using SaveAndCloseViewModel or CancelAndCloseViewModel or CloseViewModel methods, the view that belongs to this view model will be automatically deactivated from the region where it is activated.

In order to start using this feature, the only thing you have to do is install an isolated package named Catel.Extensions.Prism, available via NuGet.