title: Interaction with ListBox in WPF Popup does not work
body: <p>I wanted to create a control that lets me select the unit for a value in a textbox. To archieve this i attached a button after the textbox and opened a popup on hover containing a ListBox with the available units.</p>
  
  <p>If i put a button in this popup all works fine, i get a hover effect and can click the button. But the ListBox does not work as expected. Doing nothing special i´am not able to click or focus the ListBox items. Setting the FocusManager.IsFocusScope to true for the popup lets me select an item with two clicks, first to focus the window, second to focus the ListBox i suppose. Moving the focus programmatically has not helped either.</p>
  
  <p>Sample Popup:</p>
  
  <pre><code>&lt;Popup x:Name="PART_UnitPopup" 
    PlacementTarget="{Binding}" 
    Placement="Bottom"&gt;
    &lt;StackPanel&gt;
      &lt;ListBox x:Name="PART_UnitPopupListBox" ItemsSource="{Binding,Path=Units}"/&gt;
      &lt;Button Content="Click me!" /&gt;
    &lt;/StackPanel&gt;
  &lt;/Popup&gt;
  </code></pre>
  
  <p></p>
  
  <p>Read some things and tried some solutions with moving focus on opened or focus events of popup, but not get this work to behave in normal style like the button does. Maybe there is also another method except of popop to accomplish this task, but it seams to be a good solution and i found a bunch of code that is said to be working and does not differ much.</p>