[C++] dotnet 读 WPF 源代码 Popup 的 StaysOpen 为 false 将会吃掉其他窗口的首次激活

<Grid>
    <Button x:Name="OpenPopupButton" HorizontalAlignment="Center" VerticalAlignment="Center"
        Content="Open Popup" Click="OpenPopupButton_OnClick"></Button>
    <Popup x:Name="Popup" StaysOpen="False" PlacementTarget="{x:Reference OpenPopupButton}">
      <Grid Background="Gray" Width="100" Height="100">
        <TextBlock HorizontalAlignment="Center" VerticalAlignment="Center">The popup</TextBlock>
      </Grid>
    </Popup>
  </Grid>

private void OpenPopupButton_OnClick(object sender, RoutedEventArgs e)
    {
      Popup.IsOpen = true;
    }

public MainWindow()
    {
      InitializeComponent();
      Loaded += MainWindow_Loaded;
    }
    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
      var window1 = new Window1();
      window1.Show();
    }

public partial class MainWindow : Window
  {
    public MainWindow()
    {
      InitializeComponent();
      Loaded += MainWindow_Loaded;
      MouseDown += MainWindow_MouseDown;
      MouseUp += MainWindow_MouseUp;
      Activated += MainWindow_Activated;
      Deactivated += MainWindow_Deactivated;
      LostFocus += MainWindow_LostFocus;
    }
    private void MainWindow_Loaded(object sender, RoutedEventArgs e)
    {
      var window1 = new Window1();
      window1.Show();
    }
    private void MainWindow_MouseUp(object sender, MouseButtonEventArgs e)
    {
      Debug.WriteLine($"MainWindow_MouseUp");
    }
    private void MainWindow_MouseDown(object sender, MouseButtonEventArgs e)
    {
      Debug.WriteLine($"MainWindow_MouseDown");
    }
    private void MainWindow_Activated(object sender, EventArgs e)
    {
      Debug.WriteLine($"MainWindow_Activated");
    }
    private void MainWindow_Deactivated(object sender, EventArgs e)
    {
      Debug.WriteLine($"MainWindow_Deactivated");
    }
    private void MainWindow_LostFocus(object sender, RoutedEventArgs e)
    {
      Debug.WriteLine($"MainWindow_LostFocus");
    }
  }

• 运行代码，默认焦点是在 Window1 上
  
• 点击 MainWindow 的空白
  

MainWindow_Activated
MainWindow_Deactivated
MainWindow_Activated
MainWindow_MouseDown
MainWindow_MouseUp

• 运行代码，默认焦点是在 Window1 上
  
• 点击 Window1 的 Open Popup 按钮
  
• 点击 MainWindow 的空白
  

MainWindow_Activated
MainWindow_Deactivated
MainWindow_MouseDown
MainWindow_MouseUp

static Popup()
    {
      EventManager.RegisterClassHandler(typeof(Popup), Mouse.LostMouseCaptureEvent, new MouseEventHandler(OnLostMouseCapture));
      // 忽略其他代码
    }
    private static void OnLostMouseCapture(object sender, MouseEventArgs e)
    {
      Popup popup = sender as Popup;
      if (!popup.StaysOpen)
      {
        PopupRoot root = popup._popupRoot.Value;
        // Reestablish capture if an element within us lost capture
        // (hence we receive the LostCapture routed event) and capture
        // is not being acquired anywhere else.
        //
        // Note we do not reestablish capture if we are losing capture
        // ourselves.
        bool reestablishCapture = e.OriginalSource != root && Mouse.Captured == null && MS.Win32.SafeNativeMethods.GetCapture() == IntPtr.Zero;
        if(reestablishCapture)
        {
          popup.EstablishPopupCapture();
          e.Handled = true;
        }
        else
        {
          // 忽略其他代码
        }
      }
    }

private void EstablishPopupCapture(bool isRestoringCapture=false)
    {
      if (!_cacheValid[(int)CacheBits.CaptureEngaged] && (_popupRoot.Value != null) &&
        (!StaysOpen))
      {
        IInputElement capturedElement = Mouse.Captured;
        PopupRoot parentPopupRoot = capturedElement as PopupRoot;
        if (parentPopupRoot != null)
        {
          if (isRestoringCapture)
          {
            // if the other PopupRoot is restoring capture back to this
            // popup, ignore mouse button events until both buttons have been
            // released.  Otherwise a mouse click outside a chain of
            // "nested" popups would dismiss two of them - one on MouseDown
            // and another on MouseUp.
            if (Mouse.LeftButton != MouseButtonState.Released ||
              Mouse.RightButton != MouseButtonState.Released)
            {
              _cacheValid[(int)CacheBits.IsIgnoringMouseEvents] = true;
            }
          }
          else
          {
            // this is a "nested" popup, invoked while another popup is open.
            // We need to restore capture to the previous popup root when
            // we're done
            ParentPopupRootField.SetValue(this, parentPopupRoot);
          }
          // in either case, taking capture away from the other PopupRoot is OK.
          capturedElement = null;
        }
        if (capturedElement == null)
        {
          // When the mouse is not already captured, we will consider the following:
          // In all cases but Modeless, we want the popup and subtree to receive
          // mouse events and prevent other elements from receiving those messages.
          Mouse.Capture(_popupRoot.Value, CaptureMode.SubTree);
          _cacheValid[(int)CacheBits.CaptureEngaged] = true;
        }
      }
    }