title: how to update WindowViewModel when there is a change in StatusBarViewModel
body: <p>I have two ViewModels WindowViewModel &amp; StatusBarViewModel. i want to updatethe property StatusBarVM in WindowViewModel when there is a change in StatusBarViewModel instance</p>
  
  <p>Following is the property in WindowViewModel</p>
  
  <pre><code>public StatusBarViewModel StatusBarVM
  </code></pre>