How can I databind a view to an already existing viewmodel in WPF?

Question

I'm working on a WPF application. This application features a main window (main view) that is 'databind-ed' to a main view model. This main view is what instantiates the main view model.

Within this main window, sub views (i.e. usercontrols) are programmatically created. The main window features a dropdown lists that allows users to select different views. Each usercontrol view has a corresponding view model.

When a user selects a dropdown option, this triggers a new view model to be created. I then use data templating to template the view model to an instance of the associated view as shown below:

      <DataTemplate DataType = "{x:Type ViewModels:MyViewModel}">
           <Views:MyView />
      </DataTemplate>

My question: How do I go about data binding 'MyView' to 'MyViewModel'? I'm assuming I need to add an appropriate datacontext to MyView.xaml, however, I don't know how to do this given the fact that 'MyView' is not creating an instance of 'MyViewModel'. I essentially want to databind my view to a previously existing view model. Any ideas?

EDIT: It turns out that my view automatically databinds to my view model's data template. However, I'm unsure why this just magically works. What's going on here?

It's not magic. It's how WPF is _designed_ and _documented_. When WPF maps the template to your view model object, it necessarily has your view model object reference, and it simply sets the `DataContext` of the top-level element of your template to that view model. It is actually quite simple, a lot simpler than the work WPF has to go to in order to actually _find_ the template you're using in the first place (why don't you think _that_ part is magic?). — Peter Duniho, Aug 16 '17 at 01:56

score 0 · Answer 1 · answered Aug 16 '17 at 01:38

you have to bind your viewmodel with contentcontrol. Like this.

<ContentControl DataContext="{Binding ViewModels}" Content="{Binding Path=CurrentlySelectedComboBoxViewModel}">
  <ContentControl.Resources>
     <DataTemplate DataType="{x:Type vm:TypeAViewModel}">
        <StackPanel>
           <local:TypeAUserControl />
           </StackPanel>
     </DataTemplate>

     <DataTemplate DataType="{x:Type vm:TypeBViewModel}">
        <StackPanel>
           <local:TypeBUserControl />
        </StackPanel>
     </DataTemplate>
  </ContentControl.Resources>
</ContentControl>

How can I databind a view to an already existing viewmodel in WPF?

1 Answers1