What is the equivalent to “OnBackKeyPress”

问题:

In Windows Phone 8.0 I used this to handle the back button:

protected override void OnBackKeyPress(CancelEventArgs e)
{
    base.OnBackKeyPress(e);        
}

This Event does not exists on the "Page" control. How can I handle a click on the back button in WP 8.1?

回答1:

Take a look at Windows.Phone.UI.Input.HardwareButtons.

If you add a Basic Page to your project then VS will add a NavigationHelper class to your project which helps with Navigating thru your App, you can also see in the source code that it is subscribing to Windows.Phone.UI.Input.HardwareButtons.BackPressed.

---

In case you want to extend handling the Back Button (managing Eventhandler queue and so on) you may take a look at this answer - the method there will help to prevent backward navigation (if you don't need it) and add some more behaviours.

回答2:

You can use Windows.Phone.UI.Input.HardwareButtons like above comment. But this event always is throwed in every page. So you can use like below example and this only is throwed in active page.

protected override void OnNavigatedTo(NavigationEventArgs e)
{
    Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
}

void HardwareButtons_BackPressed(object sender, Windows.Phone.UI.Input.BackPressedEventArgs e)
{
    e.Handled = true;
    Windows.Phone.UI.Input.HardwareButtons.BackPressed -= HardwareButtons_BackPressed;
    // Navigate to a page
}

I solve my problem with this way.

回答3:

Im migrating my wp8 proyect to wp8.1 universal, so to not touch too much my code I do:

In my page base class, in the constructor, I added:

 public VBasePage()
    {
        Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
    } 

And then:

private void HardwareButtons_BackPressed(object sender, BackPressedEventArgs e)
    {
        var args = new CancelEventArgs();
        OnBackKeyPress(args);
        if (args.Cancel)
        {
            e.Handled = true;
        }
    }
protected virtual void OnBackKeyPress(CancelEventArgs e)
    {
    }

So I can use my current overrides for OnBackKeyPress method