解決WPF下popup不隨着window一塊兒移動的問題

/// <summary>
/// Popup幫助類，解決Popup設置StayOpen="True"時，移動窗體或者改變窗體大小時，Popup不隨窗體移動的問題
/// </summary>
public class PopopHelper
{
    public static DependencyObject GetPopupPlacementTarget(DependencyObject obj)
    {
        return (DependencyObject)obj.GetValue(PopupPlacementTargetProperty);
    }

    public static void SetPopupPlacementTarget(DependencyObject obj, DependencyObject value)
    {
        obj.SetValue(PopupPlacementTargetProperty, value);
    }

    public static readonly DependencyProperty PopupPlacementTargetProperty =
        DependencyProperty.RegisterAttached("PopupPlacementTarget", typeof(DependencyObject), typeof(PopopHelper), new PropertyMetadata(null, OnPopupPlacementTargetChanged));

    private static void OnPopupPlacementTargetChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue != null)
        {
            DependencyObject popupPopupPlacementTarget = e.NewValue as DependencyObject;
            Popup pop = d as Popup;

            Window w = Window.GetWindow(popupPopupPlacementTarget);
            if (null != w)
            {
                //讓Popup隨着窗體的移動而移動
                w.LocationChanged += delegate
                {
                    var mi = typeof(Popup).GetMethod("UpdatePosition", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
                    mi.Invoke(pop, null);
                };
                //讓Popup隨着窗體的Size改變而移動位置
                w.SizeChanged += delegate
                {
                    var mi = typeof(Popup).GetMethod("UpdatePosition", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
                    mi.Invoke(pop, null);
                };
            }
        }
    }
}

使用方法：

<Popup x:Name="popusBottom2" IsOpen="True" local:PopopHelper.PopupPlacementTarget="{Binding ElementName=PCheckBox2}" AllowsTransparency="True" PopupAnimation="Fade" HorizontalOffset="5" VerticalOffset="-420">
　　<Image x:Name="panel_preview" Height="100" Width="100"></Image>
</Popup>