How to show a hidden window?

Question

I am developing an add in for excel. At some point, I can receive async events. I need to be able to show the Excel window if hidden on these events.

I am able to store the Hwnd property, which I believe must be an immutable int/reference to identify my Excel window.

Can someone elaborate on this Hwnd ? and explain how I can show a hidden window from C# using it ?

Thanks in advance folks ;)

UPDATE : shortly, that was the piece of code that sorted my problems :

    /// <summary>Enumeration of the different ways of showing a window using
    /// ShowWindow</summary>
    private enum WindowShowStyle : uint
    {
        /// <summary>Hides the window and activates another window.</summary>
        /// <remarks>See SW_HIDE</remarks>
        Hide = 0,
        /// <summary>Activates and displays a window. If the window is minimized
        /// or maximized, the system restores it to its original size and
        /// position. An application should specify this flag when displaying
        /// the window for the first time.</summary>
        /// <remarks>See SW_SHOWNORMAL</remarks>
        ShowNormal = 1,
        /// <summary>Activates the window and displays it as a minimized window.</summary>
        /// <remarks>See SW_SHOWMINIMIZED</remarks>
        ShowMinimized = 2,
        /// <summary>Activates the window and displays it as a maximized window.</summary>
        /// <remarks>See SW_SHOWMAXIMIZED</remarks>
        ShowMaximized = 3,
        /// <summary>Maximizes the specified window.</summary>
        /// <remarks>See SW_MAXIMIZE</remarks>
        Maximize = 3,
        /// <summary>Displays a window in its most recent size and position.
        /// This value is similar to "ShowNormal", except the window is not
        /// actived.</summary>
        /// <remarks>See SW_SHOWNOACTIVATE</remarks>
        ShowNormalNoActivate = 4,
        /// <summary>Activates the window and displays it in its current size
        /// and position.</summary>
        /// <remarks>See SW_SHOW</remarks>
        Show = 5,
        /// <summary>Minimizes the specified window and activates the next
        /// top-level window in the Z order.</summary>
        /// <remarks>See SW_MINIMIZE</remarks>
        Minimize = 6,
        /// <summary>Displays the window as a minimized window. This value is
        /// similar to "ShowMinimized", except the window is not activated.</summary>
        /// <remarks>See SW_SHOWMINNOACTIVE</remarks>
        ShowMinNoActivate = 7,
        /// <summary>Displays the window in its current size and position. This
        /// value is similar to "Show", except the window is not activated.</summary>
        /// <remarks>See SW_SHOWNA</remarks>
        ShowNoActivate = 8,
        /// <summary>Activates and displays the window. If the window is
        /// minimized or maximized, the system restores it to its original size
        /// and position. An application should specify this flag when restoring
        /// a minimized window.</summary>
        /// <remarks>See SW_RESTORE</remarks>
        Restore = 9,
        /// <summary>Sets the show state based on the SW_ value specified in the
        /// STARTUPINFO structure passed to the CreateProcess function by the
        /// program that started the application.</summary>
        /// <remarks>See SW_SHOWDEFAULT</remarks>
        ShowDefault = 10,
        /// <summary>Windows 2000/XP: Minimizes a window, even if the thread
        /// that owns the window is hung. This flag should only be used when
        /// minimizing windows from a different thread.</summary>
        /// <remarks>See SW_FORCEMINIMIZE</remarks>
        ForceMinimized = 11
    }

    [DllImport("user32.dll")]
    static extern bool ShowWindow(IntPtr hWnd, WindowShowStyle nCmdShow);

    static void ContentClick(object obj, EventArgs ea)
    {
        Microsoft.Office.Interop.Excel.Application oExcelApp = (Microsoft.Office.Interop.Excel.Application)System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application");
        oExcelApp.Visible = true;
        ShowWindow( (System.IntPtr) Globals.ThisWorkbook.Application.Hwnd, WindowShowStyle.ShowMaximized);
    }

Answer 1

hWnd means Window Handle. It's an identifying handle for the window instance.

As for showing it, you could use the user32.ShowWindow API. Here's the P/Invoke signature, courtesy of pinvoke.net:

[DllImport("user32.dll")]
static extern bool ShowWindow(IntPtr hWnd, ShowWindowCommands nCmdShow);

And here's the ShowWindowCommands enum:

enum ShowWindowCommands
{
    /// <summary>
    /// Hides the window and activates another window.
    /// </summary>
    Hide = 0,
    /// <summary>
    /// Activates and displays a window. If the window is minimized or
    /// maximized, the system restores it to its original size and position.
    /// An application should specify this flag when displaying the window
    /// for the first time.
    /// </summary>
    Normal = 1,
    /// <summary>
    /// Activates the window and displays it as a minimized window.
    /// </summary>
    ShowMinimized = 2,
    /// <summary>
    /// Maximizes the specified window.
    /// </summary>
    Maximize = 3, // is this the right value?
    /// <summary>
    /// Activates the window and displays it as a maximized window.
    /// </summary>      
    ShowMaximized = 3,
    /// <summary>
    /// Displays a window in its most recent size and position. This value
    /// is similar to <see cref="Win32.ShowWindowCommand.Normal"/>, except
    /// the window is not activated.
    /// </summary>
    ShowNoActivate = 4,
    /// <summary>
    /// Activates the window and displays it in its current size and position.
    /// </summary>
    Show = 5,
    /// <summary>
    /// Minimizes the specified window and activates the next top-level
    /// window in the Z order.
    /// </summary>
    Minimize = 6,
    /// <summary>
    /// Displays the window as a minimized window. This value is similar to
    /// <see cref="Win32.ShowWindowCommand.ShowMinimized"/>, except the
    /// window is not activated.
    /// </summary>
    ShowMinNoActive = 7,
    /// <summary>
    /// Displays the window in its current size and position. This value is
    /// similar to <see cref="Win32.ShowWindowCommand.Show"/>, except the
    /// window is not activated.
    /// </summary>
    ShowNA = 8,
    /// <summary>
    /// Activates and displays the window. If the window is minimized or
    /// maximized, the system restores it to its original size and position.
    /// An application should specify this flag when restoring a minimized window.
    /// </summary>
    Restore = 9,
    /// <summary>
    /// Sets the show state based on the SW_* value specified in the
    /// STARTUPINFO structure passed to the CreateProcess function by the
    /// program that started the application.
    /// </summary>
    ShowDefault = 10,
    /// <summary>
    ///  <b>Windows 2000/XP:</b> Minimizes a window, even if the thread
    /// that owns the window is not responding. This flag should only be
    /// used when minimizing windows from a different thread.
    /// </summary>
    ForceMinimize = 11
}

Answer 2

HWnd is a windows handle, in C# it is really an IntPtr type. Try creating a wrapper class based on IWin32Window and use that when calling Show() e.g.

public class WndWrapper : IWin32Window
{
    IntPtr m_Handle;
    public WndWrapper(long pHandle)
    {
        m_Handle = (IntPtr)pHandle;
    }

    #region IWin32Window Members

    public IntPtr Handle
    {
        get { return m_Handle; }
    }

    #endregion
}

Then call it like this:

WndWrapper oWnd = new WndWrapper(pHandle);
MyForm oDlg = new MyForm();
oDlg.Show(oWnd);

Just be careful, as HWND elements are unmanaged you will be responsible for ensuring that they are disposed of when required.