private void UpdateDragPosition()
        {
            if (_dragService == null)
            {
                _dragService = new DragService(this);
                SetIsDragging(true);
            }

            var mousePosition = this.TransformToDeviceDPI(Win32Helper.GetMousePosition());

            _dragService.UpdateMouseLocation(mousePosition);
        }
        protected virtual IntPtr FilterMessage(
            IntPtr hwnd,
            int msg,
            IntPtr wParam,
            IntPtr lParam,
            ref bool handled
            )
        {
            handled = false;

            switch (msg)
            {
            case Win32Helper.WM_ACTIVATE:
                if (((int)wParam & 0xFFFF) == Win32Helper.WA_INACTIVE)
                {
                    if (lParam == this.GetParentWindowHandle())
                    {
                        Win32Helper.SetActiveWindow(_hwndSrc.Handle);
                        handled = true;
                    }
                }
                break;

            case Win32Helper.WM_EXITSIZEMOVE:
                UpdatePositionAndSizeOfPanes();

                if (_dragService != null)
                {
                    bool dropFlag;
                    var  mousePosition = this.TransformToDeviceDPI(Win32Helper.GetMousePosition());
                    _dragService.Drop(mousePosition, out dropFlag);
                    _dragService = null;
                    SetIsDragging(false);

                    if (dropFlag)
                    {
                        InternalClose();
                    }
                }

                break;

            case Win32Helper.WM_MOVING:
            {
                UpdateDragPosition();
            }
            break;

            case Win32Helper.WM_LBUTTONUP:     //set as handled right button click on title area (after showing context menu)
                if (_dragService != null && Mouse.LeftButton == MouseButtonState.Released)
                {
                    _dragService.Abort();
                    _dragService = null;
                    SetIsDragging(false);
                }
                break;

            case Win32Helper.WM_SYSCOMMAND:
                IntPtr wMaximize = new IntPtr(Win32Helper.SC_MAXIMIZE);
                IntPtr wRestore  = new IntPtr(Win32Helper.SC_RESTORE);
                if (wParam == wMaximize || wParam == wRestore)
                {
                    UpdateMaximizedState(wParam == wMaximize);
                }
                break;
            }



            return(IntPtr.Zero);
        }