title: Datagrid value does not change
body: <p>I have a TextBox in CellEditingTemplate in datagird.
  When I change its value but it is not reflected to new value.  </p>
  
  <pre><code>&lt;TextBox Text="{Binding Path=Firstname}" Grid.Column="1" Width="80"  &gt;&lt;/TextBox&gt;
  </code></pre>
  
  <p>How can I do this?</p>