Dump Object for ComObject using dynamic?

Question

I'm trying (without luck) to implement an "Object Dumper" for objects I'm accessing in the Office Type Library.

It must be possibly, because VS's debug window has a "dynamic view" for the System.__ComObject objects that effectively does what I want.

Any ideas?

Answer 1

I have also created a method for getting an interface that can be used for accessing the object. Use:

using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;

You have to have an IDispatch interface in your code:

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

    [PreserveSig] 
    int GetTypeInfo( 
        [MarshalAs(UnmanagedType.U4)] int iTInfo, 
        [MarshalAs(UnmanagedType.U4)] int lcid, 
        out System.Runtime.InteropServices.ComTypes.ITypeInfo ppTInfo); 

    [PreserveSig] 
    int GetIDsOfNames( 
        ref Guid riid, 
        [MarshalAs(UnmanagedType.LPArray, ArraySubType = UnmanagedType.LPWStr)] 
        string[] rgszNames, 
        int cNames, 
        int lcid, 
        [MarshalAs(UnmanagedType.LPArray)] int[] rgDispId); 

    [PreserveSig] 
    int Invoke( 
        int dispIdMember, 
        ref Guid riid, 
        uint lcid, 
        ushort wFlags, 
        ref System.Runtime.InteropServices.ComTypes.DISPPARAMS pDispParams, 
        out object pVarResult, 
        ref System.Runtime.InteropServices.ComTypes.EXCEPINFO pExcepInfo, 
        IntPtr[] puArgErr); 
}

My method casts COM object to IDispatch, gains unmanaged type info, gets object type GUID from non-public Marshal method GetTypeInfoGuid and then searchs it in current AppDomain's assemblies.

internal static Func<ITypeInfo,Guid> GetTypeInfoGuid = (Func<ITypeInfo,Guid>)Delegate.CreateDelegate(typeof(Func<ITypeInfo,Guid>), typeof(Marshal).GetMethod("GetTypeInfoGuid", BindingFlags.NonPublic | BindingFlags.Static, null, new[]{typeof(ITypeInfo)}, null), true);
public static Type GetCOMObjectType(object comobject)
{
    if(!Marshal.IsComObject(comobject))
    {
        throw new ArgumentException("This is not COM object.", "comobject");
    }
    IDispatch dispatch = (IDispatch)comobject;
    ITypeInfo info;
    dispatch.GetTypeInfo(0,0, out info);
    Guid guid = GetTypeInfoGuid(info);
    foreach(Assembly a in AppDomain.CurrentDomain.GetAssemblies())
    {
        foreach(Type t in a.GetTypes())
        {
            if(t.IsInterface && t.IsImport && t.GUID == guid)
            {
                return t;
            }
        }
    }
    return Type.GetTypeFromCLSID(guid);
}

If the appropriate type isn't found, the method will return type of System.__ComObject. However, you can get GUID property value from it, so at least you will get the GUID. Usage:

object controls = axWindowsMediaPlayer1.cdromCollection;
Type t = GetCOMObjectType(controls);
Console.WriteLine(t);
Console.WriteLine(t.GUID);
/*Output:
  WMPLib.IWMPCdromCollection
  ee4c8fe2-34b2-11d3-a3bf-006097c9b344 */

Hope this helps. Good luck. ☺

Edit: Found an easier but slower method:

object controls = axWindowsMediaPlayer1.cdromCollection;
IDispatch dispatch = (IDispatch)controls;
ITypeInfo info;
dispatch.GetTypeInfo(0,0, out info);
Type t = Marshal.GetTypeForITypeInfo(Marshal.GetIUnknownForObject(info));
Console.WriteLine(t);