How to get type of COM object

Question

I am referencing a COM library in Visual Studio, so it has automatically created the corresponding Interop assembly for me. I would like to do a GetType() on these com objects, but they always return System.__ComObject. Querying them for an interface works though:

bool isOfType = someComeObject is ISomeComObject; //this works

But what I really want is this to return the actual type of the com object:

Type type = someComeObject.GetType(); //returns System.__ComObject :-(

Does anyone know how to do what I want to do?

Answer 1

Add reference to Microsoft.VisualBasic.dll and then:

Microsoft.VisualBasic.Information.TypeName(someCOMObject)

MSDN reference here.

Answer 2

The accepted answer by Darin requires a dependency to Microsoft.VisualBasic.dll. If you don't want to have that you can use this simple helper class:

public static class TypeInformation
{
    public static string GetTypeName(object comObject)
    {
        var dispatch = comObject as IDispatch;

        if (dispatch == null)
        {
            return null;
        }

        var pTypeInfo = dispatch.GetTypeInfo(0, 1033);

        string pBstrName;
        string pBstrDocString;
        int pdwHelpContext;
        string pBstrHelpFile;
        pTypeInfo.GetDocumentation(
            -1, 
            out pBstrName, 
            out pBstrDocString, 
            out pdwHelpContext, 
            out pBstrHelpFile);

        string str = pBstrName;
        if (str[0] == 95)
        {
            // remove leading '_'
            str = str.Substring(1);
        }

        return str;
    }

    [ComImport]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    [Guid("00020400-0000-0000-C000-000000000046")]
    private interface IDispatch
    {
        int GetTypeInfoCount();

        [return: MarshalAs(UnmanagedType.Interface)]
        ITypeInfo GetTypeInfo(
            [In, MarshalAs(UnmanagedType.U4)] int iTInfo,
            [In, MarshalAs(UnmanagedType.U4)] int lcid);

        void GetIDsOfNames(
            [In] ref Guid riid,
            [In, MarshalAs(UnmanagedType.LPArray)] string[] rgszNames,
            [In, MarshalAs(UnmanagedType.U4)] int cNames,
            [In, MarshalAs(UnmanagedType.U4)] int lcid,
            [Out, MarshalAs(UnmanagedType.LPArray)] int[] rgDispId);
    }
}

Answer 3

You've basically figured it out. GetType() on a COM object is going to give you System.__ComObject, and you have to try to cast it to something else to see what the object really is.

Answer 4

I stumbled upon this question a few days ago while I was looking for the full type name of a System.__ComObject object. I ended up getting the type name using Darin's solution and then looping through all classes in all assemblies to test the match:

    typeName = Microsoft.VisualBasic.Information.TypeName(someCOMObject);
    foreach (System.Reflection.Assembly assembly in AppDomain.CurrentDomain.GetAssemblies())
    { 
        foreach (Type type in assembly.GetTypes())
        {
            if ((someCOMObject as type)!=null)
                fullTypeName = type.FullName;
        }
    }

Not the fastest and most elegant solution, but it worked.