Casting generic COM object to a specific .NET class

Question

I'm not a C# programmer so excuse me if it's a silly question, but I can't find any solutions.

I have an Object. It's a COM object and its ToString() returns "System.__comObject". When examining its inner contents with debugger I can see that this object has a property called Object and it's an instance of the actual class that I want. However, Object class has no property Object, and when I'm trying to cast the object itself to the desired type I get an exception. How should COM object be converted to a .NET object?

You can't, the best you can do is cast it to an interface that matches one of the COM interfaces that object implements — Mgetz
– Mgetz, Commented Oct 7, 2013 at 14:14
Your question seems to indicate you have access to the native code, if that's the case you can look at the objects native declaration. But if you can I would highly suggest using Tlbimp to create a .NET library to do the interop for you. — Mgetz
– Mgetz, Commented Oct 7, 2013 at 14:18
@Mgetz: no, it's Microsoft library and it's very poorly documented. I certainly don't have the declaration for this object. In fact, I can only guess it's type, which is exactly what I'm trying to do. — Violet Giraffe
– Violet Giraffe, Commented Oct 7, 2013 at 14:21
Which library? It may already have a Primary Interop Assembly. — Mgetz
– Mgetz, Commented Oct 7, 2013 at 14:21

Tim S. · Accepted Answer · 2013-10-07 14:18:33Z

3

If you know what type you'd like it to be, you could set up a method to convert it yourself, using dynamic to access the properties:

public static MyObject ConvertFromComObject(dynamic comObject)
{
    return comObject.Object;
}
// or, if that doesn't work:
public static MyObject ConvertFromComObject(dynamic comObject)
{
    return new MyObject { MyProperty = comObject.Object.MyProperty };
}
// or maybe
public static MyObject ConvertFromComObject(dynamic comObject)
{
    return new MyObject { MyProperty = comObject.MyProperty };
}

answered Oct 7, 2013 at 14:18

Tim S.

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2 Comments

Violet Giraffe Over a year ago

This works, thanks a lot! Can I make it work in-line, without a standalone method?

Tim S. Over a year ago

@VioletGiraffe Yes of course. Just cast to dynamic, e.g. MyObject myObj = ((dynamic)comObject).Object;, or declare your comObject as dynamic from the start: dynamic comObject = SomeCom.GetObject(); comObject.Object.DoSomething();.

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