title: wpf combobox data binding xml
body: <p>I want to display all groupnames (contact_grname) into my combobox, but only one item is showing up !
  Why is that ?!</p>
  
  <p></p>
  
  <pre><code>&lt;XmlDataProvider x:Key="TeleData" XPath="/response/contacts/contact"&gt;
  
  &lt;/XmlDataProvider&gt;
  
  &lt;CollectionViewSource x:Key="TeleView"  Source="{StaticResource TeleData}" &gt;
      &lt;CollectionViewSource.SortDescriptions&gt;
          &lt;scm:SortDescription PropertyName="contact_name" Direction="Ascending" /&gt;
  
      &lt;/CollectionViewSource.SortDescriptions&gt;
  
      &lt;CollectionViewSource.GroupDescriptions&gt;
          &lt;dat:PropertyGroupDescription PropertyName="contact_grname" /&gt;
  
      &lt;/CollectionViewSource.GroupDescriptions&gt;
  &lt;/CollectionViewSource&gt;
  </code></pre>
  
  <p></p>
  
  <pre><code>&lt;ComboBox ItemsSource="{Binding Source={StaticResource TeleView}, XPath=contact_grname}" /&gt;
  </code></pre>
  
  <p>my xml file:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="ISO-8859-1"?&gt;
  &lt;response&gt;
      &lt;contacts&gt;
          &lt;contact&gt;
              &lt;contact_grname&gt;group1&lt;/contact_grname&gt;
              &lt;contact_name&gt;Bart&lt;/contact_name&gt;
          &lt;/contact&gt;
          &lt;contact&gt;
              &lt;contact_grname&gt;group1&lt;/contact_grname&gt;
              &lt;contact_name&gt;Eric&lt;/contact_name&gt;
          &lt;/contact&gt;
          &lt;contact&gt;
              &lt;contact_grname&gt;group2&lt;/contact_grname&gt;
              &lt;contact_name&gt;Mike&lt;/contact_name&gt;
          &lt;/contact&gt;
      &lt;/contacts&gt;
  &lt;/response&gt;
  </code></pre>
  
  <p>Just group1 is showing up (one time).
  When I use StaticResource TeleData instead of TeleView in combobox, then all groupnames are displayed (but there are doubles values because not grouped that way)</p>
  
  <p>Expected output in combobox:</p>
  
  <ul>
  <li>group1</li>
  <li>group2</li>
  </ul>
  
  <p>Now I have (with TeleView):</p>
  
  <ul>
  <li>group1</li>
  </ul>
  
  <p>and if I use Teledata:</p>
  
  <ul>
  <li>group1</li>
  <li>group1</li>
  <li>group2</li>
  </ul>