title: WPF Data Binding with StringFormat when UpdateSourceTrigger is PropertyChanged
body: <p>I want to have a textbox append a specific string once the user tabs out of the control, i.e. LostFocus, however I prefer the textbox to validate as the user types, so <code>UpdateSourceTrigger</code> is set to <code>PropertyChanged</code>. </p>
  
  <p>Is there a way to get this to work in WPF? </p>
  
  <p>Looked at this <a href="https://stackoverflow.com/questions/987120/updatesourcetriggerpropertychanged-and-converter">question</a> which is similar but wondering if there is a cleaner solution?</p>
  
  <p>My XAML is:</p>
  
  <pre><code>    &lt;TextBox Text="{Binding Path=MyBindingPath, 
                              StringFormat='\{0} -HELLO',
                              TargetNullValue={x:Static sys:String.Empty},
                              ValidatesOnDataErrors=True,   
                              NotifyOnValidationError=True,    
                              UpdateSourceTrigger=PropertyChanged}"/&gt;
  </code></pre>