title: Two-way databinding: Updating textbox not updating bound property
body: <p>I am databinding a textbox of a <code>UserControl</code> to a property as follows.</p>
  
  <pre><code>&lt;TextBox Name="txtData" Text="{Binding MyData, Mode=TwoWay}"/&gt;
  </code></pre>
  
  <p>But when I click the Submit button on the page that hosts the usercontrol after entering some text in the <code>txtData</code> textbox of the usercontrol, <code>userControl.MyData</code> returns <code>null</code>. What can I do to have the <code>txtData.text</code> value be assigned to property other than through <code>TextChanged</code>event?</p>