How to get type of COM object

.net reflection com interop com-interop

19,623

Solution 1

Add reference to Microsoft.VisualBasic.dll and then:

Microsoft.VisualBasic.Information.TypeName(someCOMObject)

MSDN reference here.

Solution 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);
    }
}

Solution 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.

19,623

Author by

Admin

Updated on June 03, 2022

Comments

Admin about 2 years
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?
Admin over 14 years

Hm..is there really no other way? Because I can't test for every possible COM object in existing, I just want the type. The reason is that I am using the type of an object as a key in a dictionary...
Admin over 14 years

I just tried this and it works! It does not return the full name though, just the class name, but that's ok for my purposes. I looked at this method in reflector which internally calls 'LegacyTypeNameOfCOMObject' but I can't figure out what it actually does.
Admin over 14 years

I wish there was something that could give me the full name of that com object to avoid clashes.
AxA over 14 years

Thanks. Any idea if this is possible in C#?
Darin Dimitrov over 14 years

Microsoft.VisualBasic.dll is a .NET assembly which can be referenced and used in every application.
AxA over 14 years

Watch out if you have COM component written in C++/ATL. You might get a different result than you expect.
Żubrówka almost 12 years

Exactly what I was looking for. Thanks!
catfood almost 12 years

Darin Dimitrov's solution is great.
nawfal over 10 years

someCOMObject as type? Not sure if that would work.
Mike over 9 years

Source code for TypeName
Robert Synoradzki over 7 years

Because it doesn't.
ErrCode over 6 years

This seems to work too - just need to ensure there is a reference to System.Runtime.InteropServices.ComTypes for ITypeInfo (Visual Studio IDE auto-suggested Microsoft.VisualStudio.OLE.Interop.ITypeInfo, but this is not the one you want!)
pwhty about 6 years

@nawfal: why not? It's trying to cast "someCOMObject" to the type "type". If it fails (and only then), the result is null. If it doesn't, then it found the correct type. (I know, it took me a few days to come up with that answer :-P)
nawfal about 6 years

@pwhty type is not a type/class in your code, it is an instance of a type. as keyword works on a type
Zev Spitz over 3 years

Is there any way to use this to get the library of the COM object? I have an object from the Word object model for which TypeName returns Shape, but I cannot cast it to Word.Shape source in VBA.
brinkdinges over 2 years

As @rpattabi mentions, this doesn't always work. In my case, it just returns "_ComObject".