WPF: Popup that is only topmost with respect to parent window. Taken from the comments at http://chriscavanagh.wordpress.com/2008/08/13/non-topmost-wpf-popup/ (Joe Gershgorin) which was in not easy to digest state. Specific for popup and Windows Forms hos

NonTopmostPopup.cs

using System;

using System.Runtime.InteropServices;

using System.Windows;

using System.Windows.Controls.Primitives;

using System.Windows.Forms;

using System.Windows.Forms.Integration;

using System.Windows.Input;

using System.Windows.Interop;

 

namespace Honeywell.Desktop.TimeControl

{

    public class PopupEx : Popup

    {

         public static readonly DependencyProperty IsTopmostProperty =

             DependencyProperty.Register("IsTopmost",

                                  typeof(bool),

                                  typeof(PopupEx),

                                  new FrameworkPropertyMetadata(false, OnIsTopmostChanged));

        

         public bool IsTopmost

         {

             get { return (bool)GetValue(IsTopmostProperty); }

             set { SetValue(IsTopmostProperty, value); }

         }

 

         private bool? _appliedTopMost;

         private bool _alreadyLoaded;

         private Form _parentForm;

 

         public PopupEx()

         {

             Loaded += PopupNonTopmostLoaded;

             Unloaded += PopupNonTopmostUnloaded;

         }

 

         private void PopupNonTopmostUnloaded(object sender, RoutedEventArgs e)

         {

             if (_parentForm == null)

             {

                 return;

             }

 

             _parentForm.Activated -= OnParentWindowActivated;

             _parentForm.Deactivate -= OnParentWindowDeactivated;

         }

 

         void PopupNonTopmostLoaded(object sender, RoutedEventArgs e)

         {

             if (_alreadyLoaded)

             {

                 return;

             }

 

             _alreadyLoaded = true;

 

             if (Child != null)

             {

                 Child.AddHandler(PreviewMouseLeftButtonDownEvent, new MouseButtonEventHandler(ChildPreviewMouseLeftButtonDown), true);

             }

 

             var wpfHandle = PresentationSource.FromVisual(this) as HwndSource;

             if (wpfHandle == null)

             {

                 return;

             }

 

             var elementHost = Control.FromChildHandle(wpfHandle.Handle) as ElementHost;

             if (elementHost == null)

             {

                 return;

             }

 

             _parentForm = elementHost.FindForm();

             if (_parentForm == null)

             {

                 return;

             }

 

             _parentForm.Activated += OnParentWindowActivated;

             _parentForm.Deactivate += OnParentWindowDeactivated;

         }

 

         private void OnParentWindowDeactivated(object sender, EventArgs e)

         {

             if (IsTopmost == false)

             {

                 SetTopmostState(IsTopmost);

             }

         }

 

         private void OnParentWindowActivated(object sender, EventArgs e)

         {

             SetTopmostState(true);

         }

 

         void ChildPreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)

         {

             SetTopmostState(true);

 

             if (!_parentForm.Focused && IsTopmost == false)

             {

                 _parentForm.Activate();

             }

         }

 

         private static void OnIsTopmostChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)

         {

             var popup = obj as PopupEx;

             if (popup != null)

             {

                 popup.SetTopmostState(popup.IsTopmost);

             }

         }

 

         protected override void OnOpened(EventArgs e)

         {

             _appliedTopMost = null;

             SetTopmostState(IsTopmost);

             base.OnOpened(e);

         }  

 

         private void SetTopmostState(bool isTop)

         {

             if (_appliedTopMost.HasValue && _appliedTopMost == isTop)

             {

                 // Don’t apply state if it’s the same as incoming state

                 return;

             }

 

             if (Child == null)

             {

                 return;

             }

 

             var hwndSource = (PresentationSource.FromVisual(Child)) as HwndSource;

             if (hwndSource == null)

             {

                 return;

             }

 

             var hwnd = hwndSource.Handle;

             RECT rect;

             if (!GetWindowRect(hwnd, out rect))

             {

                 return;

             }

 

             if (isTop)

             {

                 SetWindowPos(hwnd, HwndTopmost, rect.Left, rect.Top, (int)Width, (int)Height, TopmostFlags);

             }

             else

             {

                 // Z-Order would only get refreshed/reflected if clicking the

                 // the titlebar (as opposed to other parts of the external

                 // window) unless I first set the popup to HWND_BOTTOM

                 // then HWND_TOP before HWND_NOTOPMOST

                 SetWindowPos(hwnd, HwndBottom, rect.Left, rect.Top, (int)Width, (int)Height, TopmostFlags);

                 SetWindowPos(hwnd, HwndTop, rect.Left, rect.Top, (int)Width, (int)Height, TopmostFlags);

                 SetWindowPos(hwnd, HwndNotopmost, rect.Left, rect.Top, (int)Width, (int)Height, TopmostFlags );

             }

 

             _appliedTopMost = isTop;

         }

 

         #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.dll")]

         private static extern bool SetWindowPos(IntPtr hWnd, IntPtr hWndInsertAfter, int x, int y, int cx, int cy, uint uFlags);

 

         static readonly IntPtr HwndTopmost = new IntPtr(-1);

         static readonly IntPtr HwndNotopmost = new IntPtr(-2);

         static readonly IntPtr HwndTop = new IntPtr(0);

         static readonly IntPtr HwndBottom = new IntPtr(1);

 

 

         const UInt32 SwpNosize = 0x0001;

         const UInt32 SwpNomove = 0x0002;

         const UInt32 SwpNozorder = 0x0004;

         const UInt32 SwpNoredraw = 0x0008;

         const UInt32 SwpNoactivate = 0x0010;

         const UInt32 SwpFramechanged = 0x0020; /* The frame changed: send WM_NCCALCSIZE */

         const UInt32 SwpShowwindow = 0x0040;

         const UInt32 SwpHidewindow = 0x0080;

         const UInt32 SwpNocopybits = 0x0100;

         const UInt32 SwpNoownerzorder = 0x0200; /* Don’t do owner Z ordering */

         const UInt32 SwpNosendchanging = 0x0400; /* Don’t send WM_WINDOWPOSCHANGING */

 

         const UInt32 TopmostFlags = SwpNoactivate | SwpNoownerzorder | SwpNosize | SwpNomove | SwpNoredraw | SwpNosendchanging;

 

         #endregion

    }

}