title: Back Button Running Amok
body: <p>On each of my app pages I am setting the back button's functionality, since I want it to do different things each time. However, when I run this on one page:</p>
  
  <pre><code>SystemNavigationManager.GetForCurrentView().BackRequested += (s, a) =&gt;
  {
      Frame.Navigate(typeof(MainPage));
      a.Handled = true;
  };
  </code></pre>
  
  <p>It also runs the back button's function on another one of my pages <em>if</em> that page has been visited first. This throws an exception, since it tries to unload a nonexistent project. Is this not the correct way to set the back button's functionality per page?</p>