title: Editable ComboBoxEdit with binding to value not in list
body: <p>I am working with a <code>ComboBoxEdit</code> from <code>DevExpress</code>.</p>
  
  <p>I have come across <a href="https://stackoverflow.com/questions/3743269/editable-combobox-with-binding-to-value-not-in-list">this</a> post, where i need the same behavior for my <code>ComboBoxEdit</code>. I need the user to be able to type a value in the <code>ComboBoxEdit</code>, even though the value is not in the list of bound objects.</p>
  
  <p>This is what i have so far:</p>
  
  <pre><code>&lt;dxe:ComboBoxEdit Name="someName"
                Height="Auto" 
                Width="Auto"
                ImmediatePopup="True"
                AutoComplete="True"
                IncrementalFiltering="True"
                IsEnabled="True"
                Visibility="Visible"
                VerticalAlignment="Stretch" 
                HorizontalAlignment="Stretch"
                IsTextEditable="True"
                VerticalContentAlignment="Stretch" 
                HorizontalContentAlignment="Right"
                Mask="###,###,###,##0.00;###,###,###,##0.00-"
                MaskType="Numeric"
                DisplayFormatString="###,###,###,##0.00;###,###,###,##0.00-"
                MaskUseAsDisplayFormat="True"
                ItemsSource="{Binding Path=SomeItemsSource}"
                DisplayMember="{Binding Path=SomeDisplayMember}"
                ValueMember="{Binding Path=SomeValueMember}"
                EditValue="{Binding Path=SomeEditValue}"&gt;
  &lt;dxe:ComboBoxEdit.StyleSettings&gt;
      &lt;dxe:ComboBoxStyleSettings /&gt;
  &lt;/dxe:ComboBoxEdit.StyleSettings&gt;
  </code></pre>
  
  <p></p>
  
  <p>Everything works fine, but i cant type in a value that is not in the list.</p>
  
  <p><strong>How can i get the same behavior as in the mentioned post for my <code>ComboBoxEdit</code>?</strong></p>