title: How can I access a page's content inside a frame?
body: <p>I have a frame inside mainwindow, inside it there's a page with panels and various contents.
  The mainwindow decides wich page to load, and then must interact with their contents (here is the problem).</p>
  
  <p>I've tried many solution and the best is this, but returns pageLogin as a null object</p>
  
  <pre><code>    _mainFrame.Source = new Uri(@"/Pages/Login.xaml", UriKind.Relative);
      Page pageLogin = this._mainFrame.Content as Page;
  </code></pre>
  
  <p>where _mainFrame is of course the name of the frame inside t mainwindow, and Login.xaml is the content with the Login_panel Stackpanel inside</p>