WP8.1 页面跳转，overwrite后退键

In 8.1 we use the below code to navigate between pages:

this.Frame.Navigate(typeof(PivotPage));

In 8.1 we need to use the event to add hardware back event:

HardwareButtons.BackPressed += HardwareButtons_BackPressed;

(However, in WP8 Silverlight, there is a direct "OnBackKeyPress"function that can be used to override)