Windows Phone 8.1 - How to handle Hardware back button GoBack with a Parameter back to the previous page

Question

I have a Windows Phone 8.1 application.

On a page when the user hits the hardware back button I want to Navigate back but also want to send a parameter to the previous page. But GoBack function doesn't take any parameter. How do I pass a parameter back so that the previous page?

This is how I have handled Hardware back button currently

In my View Constructor

HardwareButtons.BackPressed += HardwareButtons_BackPressed;

The event handler

void HardwareButtons_BackPressed(object sender, BackPressedEventArgs e)
{
    Frame rootFrame = Window.Current.Content as Frame;
    if (rootFrame != null && rootFrame.CanGoBack)
    {
        rootFrame.GoBack();
        e.Handled = true;
    }
}

I would be very glad if someone can point me in the right direction. Thanks in Advance.

Answer 1

I solved this problem using singleton pattern where i created a controller class seen by all the mobile pages and through it i passes messages through them. Hope this answer helps you

Answer 2

There are more than one way to handle this properly depending on the architecture of your app/project. Here are a couple of possible solutions:

1 - public (static) property object on App.xaml.cs. This way you can set the object from anywhere, and read it from anywhere.

public sealed partial class App : Application
{
    ............

    public static SomeType SomeObjectIPreferToShareAcrossApp { get; set; }

    ............
}

Then there's your backpressed handler:

void HardwareButtons_BackPressed(object sender, BackPressedEventArgs e)
{
    Frame rootFrame = Window.Current.Content as Frame;
    if (rootFrame != null && rootFrame.CanGoBack)
    {
        App.SomeObjectIPreferToShareAcrossApp = this.someObjectIHaveOnlyOnThisPage;
        rootFrame.GoBack();
        e.Handled = true;
    }
}

Then when you navigate to a page, check if that object is set, read it, and reset it.

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    if (e.NavigationMode == NavigationMode.Back)
    {
        if (App.SomeObjectIPreferToShareAcrossApp != null)
        {
            // yay, do something :)
            App.SomeObjectIPreferToShareAcrossApp = null;
        }
    }
}

I'm sure some people would object to this way of sharing because it may be error-prone and ugly.

2 - Some sort of event aggregator implementation, meaning that you publish/send a certain message or an object from a publisher to all of the subscribers.

3 - Shared ViewModel instances

There are other ways, but again - it depends on the architecture of your project/app.

Answer 3

Create a class with something like:

  using System;

namespace SimpleMVVM.Model
{  
    public class Customer
    {
        public int CustomerID
        {
            get; 
            set;   
        }

        public string FullName
        {
            get;
            set;
        }

        public string Phone
        {
            get; 
            set;
        }
    }
}

And then you can assign/get these through your pages, rather than sending variables between pages.

Answer 4

You must control to e.Handled like this:

        Frame rootFrame = Window.Current.Content as Frame;
        if (rootFrame != null && rootFrame.CanGoBack && !e.Handled)
        {
            rootFrame.GoBack();
            e.Handled = true;
        }

If you don't control to e.Handled, HardwareButtons.BackPressed event continue to back stack deep.