Windows Phone 7- 返回键

//"返回键"只能用于返回上一页面。只是在有键盘、context菜单或弹出窗口时，这个返回操作是关闭键盘、取消context菜单或者弹出窗口。　//　如果页面中有弹出窗口，按"返回键"应取消弹出窗口，而不是退回到上一页面，Page类提供了可重载的OnBackKeyProcess方法，可供处理此逻辑： protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)        {            if (popup.IsOpen)            {                popup.IsOpen = false;                e.Cancel = true;            }                                base.OnBackKeyPress(e);        } 　//　有些情况下需要提醒用户是否要退出当前页面(返回上一页面),例如提醒用户保存当前页。此时可重载OnBackKeyProcess方法如下：protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)        {                        if (_isNewList)            {                if (!popupSavePromotion.IsOpen)//promotion not opened yet, show it                {                    e.Cancel = true;                    popupSavePromotion.IsOpen = true;                }                else if (popupSavePromotion.IsOpen)//promotion already showed, if back key hit again, then close promotion and allow back key process continue                {                    popupSavePromotion.IsOpen = false;                }            }                       base.OnBackKeyPress(e);        }