/// 
/// Popup帮助类，解决Popup设置StayOpen="True"时，移动窗体或者改变窗体大小时，Popup不随窗体移动的问题/// 
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)            {                //让Popup随着窗体的移动而移动                w.LocationChanged += delegate                {                    var mi = typeof(Popup).GetMethod("UpdatePosition", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);                    mi.Invoke(pop, null);                };                //让Popup随着窗体的Size改变而移动位置                w.SizeChanged += delegate                {                    var mi = typeof(Popup).GetMethod("UpdatePosition", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);                    mi.Invoke(pop, null);                };            }        }    }}