title: Change applicationbar buttonicon at runtime
body: <p>I'm developing a WP7 app and the application needs to change the icon of a button on the application bar given the state of a request.
  I have tried:</p>
  
  <pre><code>if (App.Servers[index].ServerState == "Enabled")
  {
    DetailsAppBar.btnStart.IconUri = new Uri("/AppBar/appbar.stop.rest.png");
  }
  
  else
  {
    DetailsAppBar.btnStart.IconUri = new Uri("/AppBar/appbar.transport.play.rest.png");
  }
  </code></pre>
  
  <p>This doesn't give me an error in the code, but it can't compile.... 
  any hints to do this is appreciated :)</p>
  
  <p>thanks</p>