title: TextBox onchange event is frining twice with placeholder in WPF
body: <p>I have added a placeholder to the Textbox using below link,</p>
  
  <p><a href="http://www.techken.in/coding/c-wpf-create-textbox-placeholder-using-xaml-code/" rel="nofollow noreferrer">http://www.techken.in/coding/c-wpf-create-textbox-placeholder-using-xaml-code/</a></p>
  
  <p>Below is the textbox syntax i used,</p>
  
  <pre><code>&lt;TextBox   Style="{StaticResource placeHolder}"  Tag="Input text" Text="
  {Binding Path=Token,Mode=OneWayToSource, 
  UpdateSourceTrigger=PropertyChanged}"  cal:Message.Attach="[Event 
  TextChanged] = [Action OnChangeEvent()]"  /&gt;
  </code></pre>
  
  <p>When placeHolder is kept event is firing twice. If I remove UpdateSourceTrigger for Textbox which is inside of placeHolder xaml I could not get the changed property value. Anyone please let me know how I can make this to hit OnChangeEvent once only with placeholder.</p>