title: Page-based action for back button
body: <p>My question is how to define own action for given page i.e. first click on back button close popup and second navigates from page?</p>
  
  <p>Since WP8.1 NavigationHelper is quite useful yet it only gives one general action for clicking back key (exiting page).</p>
  
  <p>I can't overwrite NavigationHelper since it gives no setters for its commands and handler for back button click is private, so I can't unpin it on entering page. Making changes in NavigationHelper seems ugly since I'm developing universal app for W8.1 &amp; WP8.1 and I have multiple pages that require custom handler for back button.</p>
  
  <p>--edit--</p>
  
  <p>Commands allows overwriting, yet I'll use original command on each page. Solution is to create new command on each page?</p>