Why does my Modal WPF dialog slip behind MS Word

Question

I have a MS Word Application Add-in written with VSTO. It contains a button used to create new Letter documents. When pressed a document is instantiated, a WPF dialog is displayed to capture information and then the information is inserted into the document.

On rare occasions, the WPF dialog slips behind MS Word. I then have to kill the Winword.exe process because the dialog is Modal. I use the following code for my WPF dialog. The OfficeDialog sub class is used to make the dialog look like a MS-Word dialog.

var view = new LetterDetailsView(ViewModel);
view.ShowDialog();

public class OfficeDialog : Window
{
    [DllImport("user32.dll")]
    static extern int GetWindowLong(IntPtr hwnd, int index);
    [DllImport("user32.dll")]
    static extern int SetWindowLong(IntPtr hwnd, int index, int newStyle);
    [DllImport("user32.dll")]
    static extern bool SetWindowPos(IntPtr hwnd, IntPtr hwndInsertAfter, int x, int y, int width, int height, uint flags);
    [DllImport("user32.dll")]
    static extern IntPtr SendMessage(IntPtr hwnd, uint msg, IntPtr wParam, IntPtr lParam);

    const int GWL_EXSTYLE = -20;
    const int WS_EX_DLGMODALFRAME = 0x0001;
    const int SWP_NOSIZE = 0x0001;
    const int SWP_NOMOVE = 0x0002;
    const int SWP_NOZORDER = 0x0004;
    const int SWP_FRAMECHANGED = 0x0020;
    const uint WM_SETICON = 0x0080;
    const int ICON_SMALL = 0;
    const int ICON_BIG = 1;

    public OfficeDialog()
    {
        this.ShowInTaskbar = false;
    }

    public new void ShowDialog()
    {
        try
        {
            var helper = new WindowInteropHelper(this);
            using (Process currentProcess = Process.GetCurrentProcess())
                helper.Owner = currentProcess.MainWindowHandle;
            base.ShowDialog();
        }
        catch (System.ComponentModel.Win32Exception ex)
        {
            Message.LogWarning(ex);
            var helper = new WindowInteropHelper(this);
            using (Process currentProcess = Process.GetCurrentProcess())
                helper.Owner = currentProcess.MainWindowHandle;
            base.ShowDialog();
        }
    }

    protected override void OnSourceInitialized(EventArgs e)
    {
        base.OnSourceInitialized(e);
        RemoveIcon(this);
        HideMinimizeAndMaximizeButtons(this);
    }

    public static void HideMinimizeAndMaximizeButtons(Window window)
    {
        const int GWL_STYLE = -16;

        IntPtr hwnd = new WindowInteropHelper(window).Handle;
        long value = GetWindowLong(hwnd, GWL_STYLE);

        SetWindowLong(hwnd, GWL_STYLE, (int)(value & -131073 & -65537));
    }

    public static void RemoveIcon(Window w)
    {
        // Get this window's handle 
        IntPtr hwnd = new WindowInteropHelper(w).Handle;

        // Change the extended window style to not show a window icon
        int extendedStyle = OfficeDialog.GetWindowLong(hwnd, GWL_EXSTYLE);
        OfficeDialog.SetWindowLong(hwnd, GWL_EXSTYLE, extendedStyle | WS_EX_DLGMODALFRAME);

        // reset the icon, both calls important
        OfficeDialog.SendMessage(hwnd, WM_SETICON, (IntPtr)ICON_SMALL, IntPtr.Zero);
        OfficeDialog.SendMessage(hwnd, WM_SETICON, (IntPtr)ICON_BIG, IntPtr.Zero);

        // Update the window's non-client area to reflect the changes
        OfficeDialog.SetWindowPos(hwnd, IntPtr.Zero, 0, 0, 0, 0, SWP_NOMOVE | SWP_NOSIZE | SWP_NOZORDER | SWP_FRAMECHANGED);
    }

    static void SetCentering(Window win, IntPtr ownerHandle)
    {
        bool isWindow = IsWindow(ownerHandle);
        if (!isWindow) //Don't try and centre the window if the ownerHandle is invalid.  To resolve issue with invalid window handle error
        {
            //Message.LogInfo(string.Format("ownerHandle IsWindow: {0}", isWindow));
            return;
        }
        //Show in center of owner if win form.
        if (ownerHandle.ToInt32() != 0)
        {
            var helper = new WindowInteropHelper(win);
            helper.Owner = ownerHandle;
            win.WindowStartupLocation = WindowStartupLocation.CenterOwner;
        }
        else
            win.WindowStartupLocation = WindowStartupLocation.CenterOwner;
    }

    [DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool IsWindow(IntPtr hWnd);

}

Answer 1

A modal dialog not being on top is the result of an incorrectly set owner. You already set the owner to the MainWindowHandle of the current process; however, in particular with multiple Word documents open, this might not be what you want.

I'd suggest to rely on the following property (introduced with Word 2013):

document.ActiveWindow.HWnd;

Apart from that there should not be the need to kill the Word process. It should be sufficient to minimize all windows (e.g. by pressing Windows Key + M)