Displaying modules in a Prism region when available

Question

I want to load modules when my app loads and have them put their views in a region (see also this MSDN article) in the Shell (the main view). I am currently loading a module on demand and it works just fine. (I load the module with a button that calls this.moduleManager.LoadModule("ModuleB"); where moduleManager is defined as [Import(AllowRecomposition = false)] private IModuleManager moduleManager;. This all comes from the ModularityWithMef.Desktop sample application.) Here's the relevant code:

Module

[ModuleExport(typeof(ModuleB), InitializationMode = InitializationMode.OnDemand)]
public class ModuleB : IModule
{
    [Import(AllowRecomposition = false)] private IRegionManager _regionManager;

    /// <summary>
    /// Initializes a new instance of the <see cref="ModuleB"/> class.
    /// </summary>
    public ModuleB()
    {
    }

    /// <summary>
    /// Notifies the module that it has be initialized.
    /// </summary>
    public void Initialize()
    {
        _regionManager.AddToRegion("ContentRegion", new ModuleBView());
    }
}

XAML region

<TabControl Regions:RegionManager.RegionName="ContentRegion" />

When I change to loading the module when available ([ModuleExport(typeof(ModuleB), InitializationMode = InitializationMode.WhenAvailable)]), I get a ModuleInitializeException when the bootstrapper is creating the Shell saying "This RegionManager does not contain a Region with the name 'ContentRegion'." This tells me that there is a timing issue with the creation of the region in the Shell and the initialization of the module.

So here's my question: How do I register the module's view with the Shell's region upon discovery and without having to use OnDemand initialization and manually load the module?

Pat Pat · Accepted Answer · 2011-01-06T21:57:17

Well this was an easy answer that was, for some reason, hard for me to find. The IRegionManager provides a RegisterViewWithRegion method that takes a function that returns the view. This allows the region manager to instantiate the view when it is ready (as opposed to using AddToRegion, which happens immediately). So the key is to use that method in the module's Initialize routine:

public void Initialize()
{
    _regionManager.RegisterViewWithRegion("ContentRegion", () => new ModuleBView());
}

While I was figuring this out, I also came up with a workaround. When the module is set to InitializationMode.OnDemand, the Shell can import the IModuleManager and use LoadModule in the ContentRendered event. This ensures that the region has been added to the region manager and that the module can add its view without a problem. If you need to iterate through the available modules, use this event handler:

public Shell()
{
    InitializeComponent();

    ContentRendered += (o, eventArgs) =>
        {
            foreach (var moduleInfo in _moduleCatalog.Modules)
            {
                _moduleManager.LoadModule(moduleInfo.ModuleName);
            }
        };
}

Displaying modules in a Prism region when available

2 Answers