我正在尝试使用调度计时器中的消息对话框在时间完成时更改用户.但有时它会给出以下错误:访问被拒绝.(来自 HRESULT 的异常:0x80070005(E_ACCESSDENIED))".如何解决?

I am trying to use message dialog in dispatch timer to alter user when the time is complete. but at times it gives following error: "Access is denied. (Exception from HRESULT: 0x80070005 (E_ACCESSDENIED))". How to resolve this?

代码:

 public DetailPage()
        {
      timer = new DispatcherTimer();
            timer.Tick += dispatcherTimer_Tick; 
            timer.Interval = new TimeSpan(0, 0, 1);
            this.txtTimer.Text = GlobalVariables.totalTime.Minutes + ":" + GlobalVariables.totalTime.Seconds + "mins";
            timer.Start();
}



  async void dispatcherTimer_Tick(object sender, object e)
    {
        if (GlobalVariables.totalTime.Minutes > 0 || GlobalVariables.totalTime.Seconds > 0)
        {
            GlobalVariables.totalTime = GlobalVariables.totalTime.Subtract(new TimeSpan(0, 0, 1));
            this.txtTimer.Text = GlobalVariables.totalTime.Minutes + ":" + GlobalVariables.totalTime.Seconds + " mins";
        }
        else
        {
            timer.Tick -= dispatcherTimer_Tick;
            timer.Stop();

            MessageDialog signInDialog = new MessageDialog("Time UP.", "Session Expired");

            // Add commands and set their callbacks
            signInDialog.Commands.Add(new UICommand("OK", (command) =>
            {
                this.Frame.Navigate(typeof(HomePage), "AllGroups");
            }));

            // Set the command that will be invoked by default
            signInDialog.DefaultCommandIndex = 1;

            // Show the message dialog
            await signInDialog.ShowAsync();
        }
    }

我在以下位置收到错误:

I am getting the error at:

 // Show the message dialog
        await signInDialog.ShowAsync();

推荐答案

就像 Jeff 所说，计时器 Tick 事件处理程序代码运行在与 UI 线程不同的线程上.您必须返回此 UI 线程来操作 UI 中的任何内容:消息对话框、更改属性等.

Like Jeff says, the timer Tick event handler code is running on a different thread than the UI thread. You'll have to get back to this UI thread to manipulate anything in the UI: message dialog, changing properties, etc.

// some code for the timer in your page
timer = new DispatcherTimer {Interval = new TimeSpan(0, 0, 1)};
timer.Tick += TimerOnTick;
timer.Start();

// event handler for the timer tick
private void TimerOnTick(object sender, object o)
{
    timer.Stop();
    var md = new MessageDialog("Test");

    this.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => md.ShowAsync());
}

请注意，我确实在事件处理程序中停止了计时器.如果您没有在显示另一个消息对话框之前及时关闭消息对话框，您也会在第二个 ShowAsync 上获得拒绝访问(因为第一个仍然打开).

Note that I do stop the timer in the event handler. If you don't close a message dialog in time before another one is shown, you'll get an access denied on the 2nd ShowAsync too (because the first is still open).