CODEWITHSUNDEEP
c#windows-phone-8back-button
Inox
Inox

Reputation: 2275

Trying to override NavigationMode.Back

I'm trying to develop a simple app for Windows Phone 8, and there are many requirements for the use of the Back Button. As I don't want the Back Button to simply GoBack in back stack, I'd like to pop up a message box to warn the user that this action will bring him back to main menu.

Problem is, this page has to be reloaded some times, and the following code stop working properly after 1 reload. The messagebox opens multiple times. And the more times I reload, the more MessageBox appears.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Navigation;
using Microsoft.Phone.Controls;
using Microsoft.Phone.Shell;
using BackButtonTests.Resources;

namespace BackButtonTests
{
public partial class MainPage : PhoneApplicationPage
{        
    public MainPage()
    {
        InitializeComponent();            
    }

    protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        base.OnNavigatedTo(e);
        NavigationService.Navigating += NavigationService_Navigating;
    }

    void NavigationService_Navigating(object sender, NavigatingCancelEventArgs e)
    {

        if (e.NavigationMode == NavigationMode.Back)
        {
            e.Cancel = true;
            MessageBox.Show("Quit");
        }
    }

    private void Restart_Click(object sender, RoutedEventArgs e)
    {
        NavigationService.Navigate(new Uri("/MainPage.xaml?reload=" + DateTime.Now.ToString(), UriKind.RelativeOrAbsolute));
        //Use this fake reload query with unique value as a way to "deceive" the system, as windowsphone does not support NavigationService.Reload, and using simply the Uri of the same page will not properly load everything
    }

    private void Quit_Click(object sender, RoutedEventArgs e)
    {
        MessageBox.Show("Quit");
    }
}
}

This is just a test code I wrote, that shows exactly the problem I'm experiencing in my actual project. Of course there are 2 buttons written in xaml.

And the code won't work until you first reload the page, as it's not NavigatedTo when it's the front page (not a problem in my actual project).

Any clues of what I'm doing wrong?

NOTE: I'm not interested in changing the event handler (to OnBackKeyPress, for instance). I'm interested in understanding what's going on with the handler I chose (NavigationService.Navigating, NavigationMode.Back). Thanks

Upvotes: 0

Views: 556

Answers (1)

David Gordon
David Gordon

Reputation: 554

Updated following additional information that clarifies the questing

Changing your navigating event handler to will mean the event isn't fired on every page in the stack

void NavigationService_Navigating(object sender, NavigatingCancelEventArgs e)
{
    NavigationService.Navigating -= NavigationService_Navigating;
    if (e.NavigationMode == NavigationMode.Back)
    {
        e.Cancel = true;
        MessageBox.Show("Quit");
    }
}

No longer neccessary

Override OnBackKeypress instead of navigating

 protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
 {
   var DoYouWantToQuit = MessageBox.Show("Are you sure you want to Quit", "Quit", MessageBoxButtons.OkCancel);
   if (DoYouWantToQuit != MessageBoxButton.Ok)
   {
      e.Cancel = true
   }
   base.OnBackKeyPress(e);
 }

Upvotes: 1

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