调用线程必须是 STA

Question

我正在尝试模拟弹丸并尝试在定时事件中只创建一次标签，因为它在参数中有一个对象，我需要在定时事件中。但是当我运行它时，我得到了这个线程错误。请帮忙！

我的代码是：

    void onTimedEvent(Object source, ElapsedEventArgs e)
    {
        particle newProjectile;
        newProjectile = new particle();

        bool LabelExist = false;
        if (LabelExist == false)
        {
            CreateLabels(newProjectile);
        }
    }

        aTimer = new System.Timers.Timer(200);
        aTimer.Elapsed += onTimedEvent;
        aTimer.Enabled = true;

    void CreateLabels(particle newProjectile)
    {
        DockPanel panelcontrol_displacement, panelcontrol_CurrentVel, panelcontrol_VerticalVel, panelcontrol_HorizontalVel, panelcontrol_Time;
        Label lbl_TimeUnits, lbl_TimeOutput, lbl_Time, lbl_DisplacementOutput, lbl_DisplacementUnits, lbl_Displacement, lbl_CurrentVel, lbl_CurrentVelOutput, lbl_HorizontalVelocityOutputs, lbl_HorizontalVelocityUnits, lbl_VerticalVelocity, lbl_HorizontalVelocity, lbl_CurrentVelUnits, lbl_VerticalVelocityOutput, lbl_VerticalVelocityUnits;
        lbl_Time = new Label();
        lbl_Time.Content = "Time";
        lbl_Time.Height = 30;
        lbl_Time.Width = 110;
        lbl_TimeOutput = new Label();
        lbl_TimeOutput.Content = "20";
        lbl_TimeOutput.Height = 30;
        lbl_TimeOutput.Width = 100;
        lbl_TimeOutput.HorizontalContentAlignment = HorizontalAlignment.Right;
        lbl_TimeUnits = new Label();
        lbl_TimeUnits.Content = "s";
        lbl_CurrentVel = new Label();
        lbl_CurrentVel.Content = "Current Velocity";
        lbl_CurrentVel.Height = 30;
        lbl_CurrentVel.Width = 110;
        lbl_CurrentVelOutput = new Label();
        lbl_CurrentVelOutput.Content = "20";
        lbl_CurrentVelOutput.Height = 30;
        lbl_CurrentVelOutput.Width = 100;
        lbl_CurrentVelOutput.HorizontalContentAlignment = HorizontalAlignment.Right;
        lbl_CurrentVelUnits = new Label();
        lbl_CurrentVelUnits.Content = "m/s";
        lbl_VerticalVelocity = new Label();
        lbl_VerticalVelocity.Content = "Verticle Velocity";
        lbl_VerticalVelocity.Height = 30;
        lbl_VerticalVelocity.Width = 110;
        lbl_VerticalVelocityOutput = new Label();
        lbl_VerticalVelocityOutput.Content = "20";
        lbl_VerticalVelocityOutput.Height = 30;
        lbl_VerticalVelocityOutput.Width = 100;
        lbl_VerticalVelocityOutput.HorizontalContentAlignment = HorizontalAlignment.Right;
        lbl_VerticalVelocityUnits = new Label();
        lbl_VerticalVelocityUnits.Content = "m/s";
        lbl_HorizontalVelocity = new Label();
        lbl_HorizontalVelocity.Content = "Horizontal Velocity";
        lbl_HorizontalVelocity.Height = 30;
        lbl_HorizontalVelocity.Width = 110;
        lbl_HorizontalVelocityOutputs = new Label();
        lbl_HorizontalVelocityOutputs.Content = "20";
        lbl_HorizontalVelocityOutputs.Height = 30;
        lbl_HorizontalVelocityOutputs.Width = 100;
        lbl_HorizontalVelocityOutputs.HorizontalContentAlignment = HorizontalAlignment.Right;
        lbl_HorizontalVelocityUnits = new Label();
        lbl_HorizontalVelocityUnits.Content = "m/s";
        lbl_Displacement = new Label();
        lbl_Displacement.Content = "Displacement";
        lbl_Displacement.Height = 30;
        lbl_Displacement.Width = 110;
        lbl_DisplacementOutput = new Label();
        lbl_DisplacementOutput.Content = "20";
        lbl_DisplacementOutput.Height = 30;
        lbl_DisplacementOutput.Width = 100;
        lbl_DisplacementOutput.HorizontalContentAlignment = HorizontalAlignment.Right;
        lbl_DisplacementUnits = new Label();
        lbl_DisplacementUnits.Content = "m/s";
        panelcontrol_HorizontalVel = new DockPanel();
        panelcontrol_CurrentVel = new DockPanel();
        panelcontrol_VerticalVel = new DockPanel();
        panelcontrol_displacement = new DockPanel();
        panelcontrol_Time = new DockPanel();
        panelcontrol_CurrentVel.Children.Add(lbl_CurrentVel);
        panelcontrol_CurrentVel.Children.Add(lbl_CurrentVelOutput);
        panelcontrol_CurrentVel.Children.Add(lbl_CurrentVelUnits);
        panelcontrol_VerticalVel.Children.Add(lbl_VerticalVelocity);
        panelcontrol_VerticalVel.Children.Add(lbl_VerticalVelocityOutput);
        panelcontrol_VerticalVel.Children.Add(lbl_VerticalVelocityUnits);
        panelcontrol_HorizontalVel.Children.Add(lbl_HorizontalVelocity);
        panelcontrol_HorizontalVel.Children.Add(lbl_HorizontalVelocityOutputs);
        panelcontrol_HorizontalVel.Children.Add(lbl_HorizontalVelocityUnits);
        panelcontrol_displacement.Children.Add(lbl_Displacement);
        panelcontrol_displacement.Children.Add(lbl_DisplacementOutput);
        panelcontrol_displacement.Children.Add(lbl_DisplacementUnits);
        panelcontrol_Time.Children.Add(lbl_Time);
        panelcontrol_Time.Children.Add(lbl_TimeOutput);
        panelcontrol_Time.Children.Add(lbl_TimeUnits);
        StkPnl_Inputs.Children.Add(panelcontrol_Time);
        StkPnl_Inputs.Children.Add(panelcontrol_CurrentVel);
        StkPnl_Inputs.Children.Add(panelcontrol_VerticalVel);
        StkPnl_Inputs.Children.Add(panelcontrol_HorizontalVel);
        StkPnl_Inputs.Children.Add(panelcontrol_displacement);
        //databinding
        Binding(newProjectile, lbl_CurrentVelOutput, "CurrentVelocity");
    }

Answer 1

您收到此错误是因为不允许从后台线程访问 UI（System.Timers.Timer.Elapsed 处理程序正在后台线程上运行）。这是因为在 WPF 中处理 UI 的所有线程都应该在 Single Threaded Apartment(STA) 中运行以进行同步。而且，后台工作人员不在 STA 中运行。

使用DispatcherTimer，而不是System.Timers.Timer。

MSDN 页面的备注部分概述了这两个计时器之间的区别。

如果在 WPF 应用程序中使用 System.Timers.Timer，则值得注意的是，System.Timers.Timer 运行在与用户界面 (UI) 线程不同的线程上。为了访问用户界面 (UI) 线程上的对象，需要使用 Invoke 或 BeginInvoke 将操作发布到用户界面 (UI) 线程的 Dispatcher。

使用 DispatcherTimer 而不是 System.Timers.Timer 的原因是 DispatcherTimer 与 Dispatcher 在同一线程上运行，并且可以在 DispatcherTimer 上设置 DispatcherPriority。