WPF是否可以拥有多个GUI线程？

Question

WPF能否拥有多个GUI线程？或者它总是只有一个GUI线程（即使我有多个窗口/对话框）？

我之所以问这个问题，是因为我有来自其他线程的事件，我想在GUI线程中处理它们（因为我需要根据这些事件修改主窗口的控件）。

顺便说一下：我知道我需要使用 Dispatcher 对象来实现此目的。那么，我可以重新表述我的问题并询问：在WPF中，所有GUI元素是否始终只有一个 Dispatcher 对象？

- Sebastian Krysmanski

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你有阅读过 WPF 线程模型文档吗？http://msdn.microsoft.com/en-us/library/ms741870.aspx - sourcenouveau

Answer 1

根据http://eprystupa.wordpress.com/2008/07/28/running-wpf-application-with-multiple-ui-threads/，我进行了一些验证。我想在这里分享结果。首先：

可以有多个GUI线程（因此可以有多个Dispatcher实例）。

然而：

仅仅创建一个新窗口（模态或非模态）并不会创建一个新的GUI线程。需要显式地创建线程（通过创建Thread的新实例）。

注意：模态对话框可能是通过使用Dispatcher.PushFrame()来实现的，该方法会阻塞调用者，同时允许事件被分发。

我创建了一个简单的WPF类（再次基于第一个答案中的链接），以验证所有这些内容。我在这里分享它，这样你就可以稍微玩一下。

MainWindow.xaml:

<Window x:Class="WindowThreadingTest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Width="250" Height="130">
  <StackPanel>
    <StackPanel Orientation="Horizontal">
      <TextBlock Text="Thread's ID is "/>
      <TextBlock x:Name="m_threadId"/>
    </StackPanel>
    <StackPanel Orientation="Horizontal">
      <TextBlock Text="Thread's threading apartment is "/>
      <TextBlock x:Name="m_threadTA"/>
    </StackPanel>
    <Button Click="OnCreateNewWindow" Content="Open New Window"/>
    <Button Click="OnAccessTest" Content="Access Test"/>
  </StackPanel>
</Window>

MainWindow.xaml.cs:

using System;
using System.Threading;
using System.Windows;
using System.Windows.Media;

namespace WindowThreadingTest {
  /// <summary>
  /// Interaction logic for MainWindow.xaml
  /// </summary>
  public partial class MainWindow : Window {
    private static uint s_windowNumber = 0;

    private readonly MainWindow m_prevWindow;

    public MainWindow() : this(null) { }

    public MainWindow(MainWindow prevWindow) {
      InitializeComponent();

      this.m_prevWindow = prevWindow;

      this.Title = String.Format("Window {0}", ++s_windowNumber);

      Thread thread = Thread.CurrentThread;
      this.m_threadId.Text = thread.ManagedThreadId.ToString();
      this.m_threadTA.Text = thread.GetApartmentState().ToString();
    }

    private void OnCreateNewWindow(object sender, RoutedEventArgs e) {
      CreateNewWindow(true, false, true);
    }

    private void CreateNewWindow(bool newThread, bool modal, bool showInTaskbar) {
      MainWindow mw = this;

      if (newThread) {
        Thread thread = new Thread(() => {
          MainWindow w = new MainWindow(this);
          w.ShowInTaskbar = showInTaskbar;

          if (modal) {
            // ShowDialog automatically starts the event queue for the new windows in the new thread. The window isn't
            // modal though.
            w.ShowDialog();
          } else {
            w.Show();
            w.Closed += (sender2, e2) => w.Dispatcher.InvokeShutdown();
            System.Windows.Threading.Dispatcher.Run();
          }
        });

        thread.SetApartmentState(ApartmentState.STA);
        thread.Start();

      } else {
        MainWindow w = new MainWindow(this);
        w.ShowInTaskbar = showInTaskbar;
        if (modal) {
          // Even modal dialogs run in the same thread.
          w.ShowDialog();
        } else {
          w.Show();
        }
      }
    }

    private void OnAccessTest(object sender, RoutedEventArgs e) {
      if (m_prevWindow == null) {
        return;
      }

      this.Background = Brushes.Lavender;
      try {
        m_prevWindow.Background = Brushes.LightBlue;
      } catch (InvalidOperationException excpt) {
        MessageBox.Show("Exception: " + excpt.Message, "Invalid Operation");
      }
      m_prevWindow.Dispatcher.Invoke((Action)(() => m_prevWindow.Background = Brushes.Green));

      this.Dispatcher.Invoke((Action)(() => {
        try {
          m_prevWindow.Background = Brushes.Red;
        } catch (InvalidOperationException excpt) {
          MessageBox.Show("Exception: " + excpt.Message, "Invalid Dispatcher Operation");
        }
      }));
    }
  }
}

- Sebastian Krysmanski

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如果你不能做到，那就是不能，加一。 - CloudyMarble