Using RegisterViewWithRegion with derived usercontrol - wpf

Question

I am writing an application with WPF using Prism and the Managed Extensibility Framework. The purpose is to allow developers to create there own 3rd party modules. To remove as much work as possible I have created some base classes in a Common module which already does most of the required work. (eg. drag n drop for views, adds MEF InheritedExportAttribute). One of these controls is called ModuleControl (derives from UserControl) shown below.
I have everything working great if my module has a view class directly derived from UserControl with one child ModuleControl in the XAML (see the examples below). This seems like a lot extra work for users. I'd like to make my view class derive from 'ModuleControl' just using code. If I do this as in the final example below, then RegisterViewWithRegion throws the following exception:
Activation error occured while trying to get instance of type ModuleView, key \"\"
System.Exception {Microsoft.Practices.ServiceLocation.ActivationException}
I realise this happens when the type can't be registered. So my questions are how can I achieve this? What am I doing wrong? Does RegisterViewWithRegion explicitly expect UserControl and nothing derived from it?
Here is an example of my first control located in Common.dll.
namespace Common.Controls
{
[InheritedExport]
public partial class ModuleControl: UserControl
{
private Point _anchor;
public ModuleControl()
{
InitializeComponent();
}
public ObservableCollection<IComponent> ModuleComponents
{
get
{
return (ObservableCollection<IComponent>)GetValue(ModuleComponentsProperty);
}
set
{
SetValue(ModuleComponentsProperty, value);
}
}
private void InitialiseCollection()
{
try
{
ModuleComponents = new ObservableCollection<IComponent>();
var components = ServiceLocator.Current.GetAllInstances(typeof(IComponent));
Assembly controlAssembly = UIHelper.FindAncestor<UserControl>(VisualTreeHelper.GetParent(this)).GetType().Assembly;
foreach (IComponent c in components)
{
if (c.ExportType.Assembly.Equals(controlAssembly))
{
ModuleComponents.Add(new Component(c.ViewType, c.Description));
}
}
}
catch (Exception e)
{
}
}
public string ModuleName
{
get
{
return (string)GetValue(ModuleNameProperty);
}
set
{
SetValue(ModuleNameProperty, value);
}
}
public static readonly DependencyProperty ModuleComponentsProperty =
DependencyProperty.Register("ModuleComponents", typeof(ObservableCollection<IComponent>), typeof(ModuleControl), new UIPropertyMetadata(null));
public static readonly DependencyProperty ModuleNameProperty =
DependencyProperty.Register("ModuleName", typeof(String), typeof(ModuleControl), new UIPropertyMetadata("No Module Name Defined"));
private void DragList_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
// Store the mouse position
_anchor = e.GetPosition(null);
}
private void DragList_PreviewMouseMove(object sender, MouseEventArgs e)
{
// Get the current mouse position
Point mousePos = e.GetPosition(null);
Vector diff = _anchor - mousePos;
if (e.LeftButton == MouseButtonState.Pressed &&
Math.Abs(diff.X) > SystemParameters.MinimumHorizontalDragDistance ||
Math.Abs(diff.Y) > SystemParameters.MinimumVerticalDragDistance)
{
// Get the dragged ListViewItem
ListView listView = sender as ListView;
ListViewItem listViewItem = UIHelper.FindAncestor<ListViewItem>((DependencyObject)e.OriginalSource);
// Initialize the drag & drop operation
if (listViewItem != null)
{
DataObject dragData = new DataObject("moduleFormat", listViewItem.Content);
DragDrop.DoDragDrop(listViewItem, dragData, DragDropEffects.Move);
}
}
}
private void moduleControl_LayoutUpdated(object sender, EventArgs e)
{
if (ModuleComponents == null)
InitialiseCollection();
}
}
Following from the example A Prism 4 Application Checklist I built the following module modifying this to use MEF instead of Unity where appropriate.:
This module is located in RandomNumbers.dll
namespace RandomNumbers
{
[ModuleExport(typeof(RandomNumberModule))]
public class RandomNumberModule: IModule
{
public void Initialize()
{
var regionManager = ServiceLocator.Current.GetInstance<IRegionManager>();
regionManager.RegisterViewWithRegion("MyRegion", typeof(ModuleView));
}
}
}
The ModuleView XAML that works looks like this:
<UserControl x:Name="userControl" x:Class="RandomNumbers.Views.ModuleView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:common="clr-namespace:Common.Base;assembly=Common"
xmlns:commonctrls="clr-namespace:Common.Controls;assembly=Common"
mc:Ignorable="d">
<commonctrls:ModuleControl x:Name="moduleControl" ModuleName="Random Number Module" />
</UserControl>
The codebehind for this is:
namespace RandomNumbers.Views
{
[Export]
public partial class ModuleView : UserControl
{
private Point startPoint;
public ModuleView()
{
InitializeComponent();
}
}
}
As already mentioned, all the above code works perfectly. However if I replace the XAML and code behind with this, then I get the exception as described. I have tried leaving out the ExportAttribute but nothing changes.
namespace RandomNumbers.Views
{
[Export(typeof(UserControl))]
public class ModuleView : ModuleControl
{
public ModuleView() : base() { }
}
}