When working with a Visual Studio Tools for Office (VSTO) project, you may want to have your add-in behave differently when the Active Workbook is inside an embedding. More specifically, the user has inserted an Excel sheet into a Word Document, for example, and has just double-clicked on it and you find that you need to detect this scenario. The trick is to know when you are in an embedded scenario and as it turns out, this is not easy to do. If you are an OLE guru, you might check the Container property on the Workbook Object:

• Workbook.Container Property (Excel)
  http://msdn.microsoft.com/en-us/library/office/ff834401.aspx

However, this property always throws an Exception for Office Document types. It specifically calls out Internet Explorer, for a reason. This property does not work with OLE Embeddings in other Office documents. You can check the path length and as I have seen in many solutions hardcoding for “Workbook in…” but this fails for multi-language solutions.

What I found you have to do is access a series of OLE properties through C# to get the information you need. And as an added bonus, not only can you determine if Excel is embedded, but you can also get the Name of the class object it is embedded inside of and the Moniker / Filename of the file it is embedded in. I created the following Extension methods for Excel:

/// <summary>
/// EXTENSION METHOD CLASS FOR EXCEL
/// </summary>
public static class ExcelExtensionMethods
{
    [DllImport("ole32.dll")]
    static extern int CreateBindCtx(uint reserved, out IBindCtx ppbc);

    /// <summary>
    /// WORKBOOK EXTENSION METHOD
    /// Checks to see if the Workbook is embeeded inside of 
    /// another ActiveX Document type, sy=uch as Word or Excel.
    /// </summary>
    /// <param name="PobjWb"></param>
    /// <returns></returns>
    public static bool IsEmbedded(this Excel.Workbook PobjWb)
    {
        if (PobjWb.Path == null || PobjWb.Path.Length == 0)
        {
            try
            {
                // requires using Microsoft.VisualStudio.OLE.Interop;
                // and you have to manually add this to reference from here:
                // C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.VisualStudio.OLE.Interop.dll
                IOleObject LobjOleObject = ((object)PobjWb) as IOleObject;
                IOleClientSite LobjPpClientSite;
                // get the client site
                LobjOleObject.GetClientSite(out LobjPpClientSite);
                // if there is one - we are embedded
                if (LobjPpClientSite != null)
                {
                    return true;
                }
                else
                {
                    // not embedded
                    return false;
                }
            }
            catch (Exception ex)
            {
                // exception
                Debug.Print(ex.ToString());
                return false;
            }
            finally { }
        }
        else
        {
            // not embedded
            return false;
        }
    }

    /// <summary>
    /// WORKBOOK EXTENSION METHOD
    /// This method return the name of the class that we
    /// are embedded inside of.
    /// If we are not embedded it return null.
    /// If there is any exception it return null.
    /// If the container cannot be accessed it returns UNKNOWN.
    /// </summary>
    /// <param name="PobjWb"></param>
    /// <returns></returns>
    public static string EmbedClassName(this Excel.Workbook PobjWb)
    {
        try
        {
            IOleObject LobjOleObject = ((object)PobjWb) as IOleObject;
            IOleClientSite LobjPpClientSite;
            // get the client site
            LobjOleObject.GetClientSite(out LobjPpClientSite);
            if (LobjPpClientSite != null)
            {
                IOleContainer LobjPpContainer;
                LobjPpClientSite.GetContainer(out LobjPpContainer);
                if (LobjPpContainer != null)
                {
                    return LobjPpContainer.GetType().Name;
                }
                else
                {
                    // something wrong - container is not valid
                    return "UNKNOWN";
                }
            }
            else
            {
                // not embedded
                return null;
            }
        }
        catch (Exception ex)
        {
            Debug.Print(ex.ToString());
            return null; // failed
        }
    }

    /// <summary>
    /// WORKBOOK EXTENSION METHOD
    /// Get the full path to the file that the workbook is embedded 
    /// inside of. 
    /// If we are not embeeded then this will return null.
    /// If we are embedded but there are issues with the container
    /// or an exception occurs, it will return null.
    /// Otherwise we get the full path and filename.
    /// </summary>
    /// <param name="PobjWb"></param>
    /// <returns></returns>
    public static string EmbedMoniker(this Excel.Workbook PobjWb)
    {
        try
        {
            IOleObject LobjOleObject = ((object)PobjWb) as IOleObject;
            IOleClientSite LobjPpClientSite;
            // get the client site
            LobjOleObject.GetClientSite(out LobjPpClientSite);
            if (LobjPpClientSite != null)
            {
                IOleContainer LobjPpContainer;
                LobjPpClientSite.GetContainer(out LobjPpContainer);
                if (LobjPpContainer != null)
                {
                    // get the moniker
                    IMoniker LobjMoniker;
                    LobjPpClientSite.GetMoniker((uint)OLEGETMONIKER.OLEGETMONIKER_FORCEASSIGN,
                                                (uint)OLEWHICHMK.OLEWHICHMK_OBJFULL,
                                                out LobjMoniker);
                    if (LobjMoniker != null)
                    {
                        // now pull the moniker display name
                        // this will be in the form of PATH!Context
                        string LstrDisplayName;
                        IBindCtx LobjCtx = null;
                        CreateBindCtx(0, out LobjCtx); // required (imported function)
                        LobjMoniker.GetDisplayName(LobjCtx, null, out LstrDisplayName);
                        // remove context is exists
                        if (LstrDisplayName.Contains("!"))
                        {
                            string[] LobjMonikerArray = LstrDisplayName.Split('!');
                            // return the first part - which should be the path
                            return LobjMonikerArray[0];
                        }
                        else
                        {
                            // return full display name
                            return LstrDisplayName;
                        }
                    }
                    else
                    {
                        // no moniker value
                        return null;
                    }
                }
                else
                {
                    // something wrong - container is not valid
                    return null;
                }
            }
            else
            {
                // not embedded
                return null;
            }
        }
        catch (Exception ex)
        {
            Debug.Print(ex.ToString());
            return null; // failed
        }
    }
}

Pay close attention to the comments, because you will not find the OLE reference you need in the References window. You will have to browse to the path given and manually select it.

Now, to use it, I hook to the WorkbookActivate event, like this:

/// <summary>
/// STARTUP
/// </summary>
/// <param name="PobjSender"></param>
/// <param name="pObjEventArgs"></param>
private void ThisAddIn_Startup(object PobjSender, System.EventArgs pObjEventArgs)
{
    Application.WorkbookActivate += new Excel.AppEvents_WorkbookActivateEventHandler(Application_WorkbookActivate);
}

/// <summary>
/// Workbook Activate event fires when any workbook is activated.
/// </summary>
/// <param name="PobjWb"></param>
void Application_WorkbookActivate(Excel.Workbook PobjWb)
{
    // call the extension method created below
    if (PobjWb.IsEmbedded())
    {
        string LstrClass = PobjWb.EmbedClassName();
        string LstrPath = PobjWb.EmbedMoniker();
        MessageBox.Show("This workbook is embedded in a [" + LstrClass + "] " +
                        "with a path of: \n\n\t" + LstrPath);
    }
}

What you can see from the code above is that on WorkbookActivate, I check to see if the workbook is embedded and if it is, then I get the Class Name by calling my other Extension Method – EmbedClassName() – and then I get the path to the file it is embedded inside of (for example, the Word document path that contains the embedded Excel sheet) by calling yet another Extension Method – EmbedMoniker().