Question

This is what I’m trying to do:

• I’m writing a UserControl that I want to be consumed by other developers.

• I want end users to be able to use my control using Dependency Properties.

  <lib:ControlView ControlsText={Binding Path=UsersOwnViewModelText} />
  

• I’m using the MVVM pattern.

• I’m binding my ViewModels to their View’s using <DataTemplates>

  <DataTemplate DataType="{x:Type local:ControlViewModel}">  
      <local:ControlView />  
  </DataTemplate>
  

So I have two questions:

1. Am I right in thinking that if a UserControl is being consumed in XAML then the UserControl must set the ViewModel as its DataContext when the control’s Loaded event fires instead of using the <DataTemplate> method?

2. How do I allow users to data bind to my control’s dependency properties while still being data bound to my ViewModel?

Answer 1

First off, I don’t think MVVM is a good choice if you are developing a UserControl that will be consumed by others. A lookless control is what you really should be developing. Jeremiah Morrill has a blog post about this subject.

With that said, you can set the datacontext with XAML if you have a default public constructor.

Inside ControlView.xaml put:

<UserControl.DataContext>
    <local:ControlViewModel />
</UserControl.DataContext>