title: WPF get current frame
body: <p>I'm making a WPF application with in the mainpage a Frame and some buttons.
  If i press Button1 my frame navigates to Page1, </p>
  
  <blockquote>
    <p>Page1 vPage1 = new Page1();<br>
    Frame.Content = vPage1;</p>
  </blockquote>
  
  <p>If i press Button2 it should only navigate to Page2 if Page1 is open in the Frame.
  How can I check if Page1 is open?</p>
  
  <p>Thx</p>