How to handle the back button on Windows Phone 7

Question

On the windows phone 7 emulator, when the hardware back button is pressed, the default behaviour is for it to close your current application. I want to override this default behaviour so that it navigates to the previous page in my application.

After some research, it seems it should be possible to do this by overriding the OnBackKeyPress method, like so:

protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
    // do some stuff ...

    // cancel the navigation
    e.Cancel = true;
}

However, clicking the back button still closes my application. Putting a breakpoint on the above method reveals that it is never called. I have another breakpoint on my application exit code, and this breakpoint is hit.

Is there something else I need to do to intercept the back button?

Answer 1

It would appear that it's not possible to override the OnBackKeyPress method to intercept the back key unless you use the Navigate method to move between pages in your application.

My previous method of navigation was to change the root visual, like:

App.Current.RootVisual = new MyPage(); 

This meant I could keep all my pages in memory so I didn't need to cache the data stored on them (some of the data is collected over the net).

Now it seems I need to actually use the Navigate method on the page frame, which creates a new instance of the page I'm navigating to.

(App.Current.RootVisual as PhoneApplicationFrame).Navigate(
                                    new Uri("/MyPage.xaml", UriKind.Relative)); 

Once I started navigating using this method, I could then override the back button handling in the way described in my question...