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");}}

MainWindow_Activated
MainWindow_DeactivatedMainWindow_Activated
MainWindow_MouseDown
MainWindow_MouseUp

MainWindow_Activated
MainWindow_DeactivatedMainWindow_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 doneParentPopupRootField.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;}}}