Question

Am using pages in my application and let me explain simply for your understanding.

I have pages A,B and C.
From page A -> page B,
page A -> page C are possible.

I need to do a action only when the page A is resumed from page B and not from page C.

How can i make it possible, can i be able to send some flag data back to page A from page B’s OnBackPressed. And if so where can i listen to get that flag data in page A.

Answer 1

You can use a QueryString. When navigating from B to A, add your QueryString to the URL:

NavigationService.Navigate(new Uri("/PageA.xaml?PreviousPage=b", UriKind.Relative));

Then, in A's OnNavigatedTomethod, you can check what the value of the PreviousPage QueryString and react accordingly if its value is b.

protected override void OnNavigatedTo(NavigationEventArgs e)  
{
     base.OnNavigatedTo(e);

     string prevPage="";

     NavigationContext.QueryString.TryGetValue("PreviousPage", out prevPage);

     if(prevPage == "b")
     {
         //code to call if A is resuming from B
     }    
}

Update based on comment (will leave the code above for others)

There are a couple of options regarding the BackKey. Firstly, you can use the code above and then delete that particular page from the history. You can do this by using the RemoveBackEntry method within the code above:

if(NavigationService.CanGoBack)
   NavigationService.RemoveBackEntry();

You can see more about the Back Stack here.

Alternatively, you could keep track of a global variable, in App.xaml.cs for example, that is updated whenever a user leaves a page. Then, in A, you can check that variable and see what the previous page was (and reset the variable if need be so that it’s not read again accidentally).