如何在Windows Phone 8.1中覆盖基本页面的HardwareButtons_BackPressed

Question

我的app中有两个页面.一个是blankPage,另一个是基本页面.在基本页面上,我想提供一条消息,如果用户按下"你确定要退出"按钮,如果是,那么返回其他地方仍然存在,使用此代码工作正常

 HardwareButtons.BackPressed += HardwareButtons_BackPressed;
private async void HardwareButtons_BackPressed(object sender, BackPressedEventArgs e)
        {
            e.Handled = true;
            MessageDialog dlg = new MessageDialog("Are you sure you want to quit you will loose all your work ?", "Warning");
            dlg.Commands.Add(new UICommand("Yes", new UICommandInvokedHandler(CommandHandler1)));
            dlg.Commands.Add(new UICommand("No", new UICommandInvokedHandler(CommandHandler1)));




            await dlg.ShowAsync();
    }



 private void CommandHandler1(IUICommand command)
        {
            var label = command.Label;
            switch (label)
            {
                case "Yes":
                    {
                        this.Frame.Navigate(typeof(MainPage));
                        break;
                    }
                case "No":
                    {
                        break;
                    }

            }

        }

但是当我按下BlankPage上的按钮时,此消息也会出现在那里,如果我添加更多内容,也会出现在所有其他基本页面中.我在做什么错？

Answer 1

您正在页面构造函数或页面加载事件中注册硬件返回按钮,并且一旦注册此事件,您就不会取消注册此事件.BackPress是应用级别.在您想要的页面上正确使用此事件注册OnNavigatedTo覆盖方法中的Back Press事件,并在OnNavigatedFrom ovrride方法中取消注册此事件.这是怎么回事.

    protected override void OnNavigatedTo(NavigationEventArgs e)
    {

        Windows.Phone.UI.Input.HardwareButtons.BackPressed += HardwareButtons_BackPressed;
    }

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