title: How to use update source trigger on Wpf Combobox which is editable?
body: <p>I have a combo box (in my wpf-mvvm app). I have set <code>IsEditable = true</code>. But the "property changed  event" is getting fired when I start typing. </p>
  
  <p>How can I set <code>UpdateSourceTrigger = Propertychanged</code> here ?</p>
  
  <p>Also..I need to call a validation function if user has entered new value ( i mean other than those available in list ..using edit functionality).</p>
  
  <p>Any help will be appreciated.</p>
  
  <pre><code>    &lt;ComboBox ItemsSource="{Binding Path = PlanTypeBasedContractNumberList }" Width="90" IsEditable="True"  
  SelectedValue="{Binding GeneralCharacteristicsDataContext.ContractNumber.Value}"&gt;
                              &lt;/ComboBox&gt;
  </code></pre>