Share context data with all children of a control

Question

I need all children of a view to know a piece of contextual information (the person they need to show). I also need the approach to be compatible with MVVM. I tried to do this with RegionContext in my Prism application. Here's my approach and problems:

I have a TabControl that I use View Injection to populate with views so that I can populate RegionContext:

From Shell.xaml:

<TabControl DockPanel.Dock="Right" cal:RegionManager.RegionName="TabRegion">

And here's my injection

//Create an instance of ContactView.xaml
contactView = CreateContactView(contact);
_regionManager.Regions["TabRegion"].Add(contactView, contactKey, true);

//"contact" being a simple entity of type Contact
RegionManager.SetRegionContext(contactViewb, contact);

What I expected was to be able to use an attached property to get the value of the RegionContext from any control that is a child of that DependencyObject (ContactView.xaml) via the RegionManager.RegionContext attached property:

From ContactView.xaml

<TextBlock Text="{Binding 
     RelativeSource={RelativeSource Self}, 
     Path=(cal:RegionManager.RegionContext)}"/>

But this doesn't work... I have to find ContactView.xaml to get it to work:

<TextBlock Text="{Binding 
     RelativeSource={RelativeSource 
          Mode=FindAncestor, 
          AncestorType={x:Type views:ContactView}}, 
     Path=(cal:RegionManager.RegionContext)}"/>

This is fine, however I'm going to allow modules to load views into ContactView and I would prefer they didn't have to know anything about ContactView.

I guess my question really is, how are you expected to load a complicated view with lots of controls and regions and have them all share one piece of context data?

What is the right way to do this? Scoped container? Write a new attached property that runs up the control hierarchy to find the RegionContext (ugh)? I'm not using RegionContext correctly? I'm open to anything. Suggest away.

Answer 1

A better design avoids using RegionContext altogether. That is a sort of poor man's dependency injection in that it can host only one object. Using a scoped Unity container into which you inject the contact would lead to better testability of the ViewModel and will avoid the inevitable conflict when needing two items in RegionContext.