title: Nested Listbox how to set parent listbox selectedItem on child listbox mouse double click
body: <p>I have a Nested <code>ListBox</code>. On inner listbox mouse double click event, I need to open a new window based on some logic and for that I need the inner ListBox SelectedItem and its corresponding Outer <code>ListBox SelectedItem</code>. How can get this in an MVVM manner?</p>
  
  <pre><code>&lt;ListBox ItemsSource="{Binding OuterCollection}"&gt;
              &lt;ListBox.ItemTemplate&gt;
                  &lt;DataTemplate&gt;
                      &lt;StackPanel Orientation="Horizontal"&gt;
                          &lt;TextBlock Text="{Binding OuterProperty1}" /&gt;
                              &lt;ListBox Width="200" ItemsSource="{Binding InnerCollection}"&gt;
                                  &lt;ListBox.ItemTemplate&gt;
                                      &lt;DataTemplate&gt;
                                          &lt;TextBlock Text="{Binding InnerProperty1}" /&gt;
                                      &lt;/DataTemplate&gt;
                                  &lt;/ListBox.ItemTemplate&gt;
                              &lt;/ListBox&gt;
                      &lt;/StackPanel&gt;
                  &lt;/DataTemplate&gt;
              &lt;/ListBox.ItemTemplate&gt;
          &lt;/ListBox&gt;
  </code></pre>
  
  <p>Things to remember:</p>
  
  <p>1) There is no relation between the inner collection and outer collection item.</p>
  
  <p>2) I'm using MVVMLight Toolkit and as a temporary solution I just passes inner ListBox Mouse Double Click event argument to the View model and traverse through the tree to find the Outer ListBox item.
  I know this is against the MVVM rules, so how can I do it in a proper MVVM manner?</p>