public class CustomPopup : Popup{public static DependencyProperty TopmostProperty = Window.TopmostProperty.AddOwner(typeof(CustomPopup), new FrameworkPropertyMetadata(false, OnTopmostChanged));public bool Topmost{get { return (bool)GetValue(TopmostProperty); }set { SetValue(TopmostProperty, value); }}private static void OnTopmostChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e){(obj as CustomPopup).UpdateWindow();}protected override void OnOpened(EventArgs e){UpdateWindow();}private void UpdateWindow(){var hwnd = ((HwndSource)PresentationSource.FromVisual(this.Child)).Handle;RECT rect;if (GetWindowRect(hwnd, out rect)){SetWindowPos(hwnd, Topmost ? -1 : -2, rect.Left, rect.Top, (int)this.Width, (int)this.Height, 0);}}#region P/Invoke imports & definitions[StructLayout(LayoutKind.Sequential)]public struct RECT{public int Left;public int Top;public int Right;public int Bottom;}[DllImport("user32.dll")][return: MarshalAs(UnmanagedType.Bool)]private static extern bool GetWindowRect(IntPtr hWnd, out RECT lpRect);[DllImport("user32", EntryPoint = "SetWindowPos")]private static extern int SetWindowPos(IntPtr hWnd, int hwndInsertAfter, int x, int y, int cx, int cy, int wFlags);#endregion}

[DllImport("user32.dll")]public static extern IntPtr WindowFromPoint(POINT Point);[DllImport("user32.dll")][return: MarshalAs(UnmanagedType.Bool)]public static extern bool GetCursorPos(out POINT lpPoint);[DllImportAttribute("user32.dll")]public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, IntPtr lParam);[DllImportAttribute("user32.dll")]public static extern bool ReleaseCapture();[StructLayout(LayoutKind.Sequential)]public struct POINT { public int X; public int Y;}        public const int WM_NCLBUTTONDOWN = 0xA1; public const int HT_CAPTION = 0x2;private void PopupMouseDown(object sender, MouseButtonEventArgs e){POINT curPos;IntPtr hWndPopup;GetCursorPos(out curPos);hWndPopup = WindowFromPoint(curPos);ReleaseCapture();SendMessage(hWndPopup, WM_NCLBUTTONDOWN, new IntPtr(HT_CAPTION), IntPtr.Zero);}

public MainWindow()
{ LocationChanged += new EventHandler(MainWindow_LocationChanged);}

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void MainWindow_LocationChanged(object sender, EventArgs e)
{
//方法1
var mi = typeof(Popup).GetMethod("UpdatePosition", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);
mi.Invoke(popBottom, null);//方法2
//popBottom.ClearValue(Popup.IsOpenProperty);//popBottom.IsOpen = true;
}

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