PRISM UserControl and ServiceReference

I'm using开发者_运维知识库 MVVM in my project and here is my question. I have a View and corresponding view-model with service reference. This view contains UserControl, which have another UserControl and it also contains nested UserControl. Last UserControl have a method which creates a popup. And in this popup i need service reference from view model. Each user control has own DataContext.

Code explanation.

View xaml:

<UserControl DataContext="{Binding ViewModel}">
   <FunctionsList/>
</UserControl>

FunctionsList xaml:

<UserControl>
   <Function1/>
   <Function2/>
   <Function3/>
   <Function4/>
</UserControl>

Function3 xaml:

<UserControl/>

Function3 code behind contains CreatePopup method, which creates dialog with a UserControl Function3Popup as Content. And Function3Popup should have Service reference.

What is the best practice here? I have awful solution to pass reference using binding but it seems discouraging to me.

Well, after all I've implemented popup with own ViewModel and resolved it from parent control using command binding in the nested child control. I think it's the best solution here.