Get value from System.__Object in C#

Question

I have a vendor specific COM interface. Intellisense shows properties while writing; thus I write something like

App.Element.Car.seats

which is somehow known to Visual Studio. In the autocomplete window, these elements are shown as properties of App, which is the COM interface to the external application. Does Visual Studio somehow read the methods and properites that are available in the dll / library?

However, call returns System.__Object, but it should be a number of some type. I do not have any documentation to the COM interface; thus I have to work just with the dll. Is there any way to get the correct type and retrieve the actual value that is contained somehow in seats?

In VB, this notation does work, but I must use C#.

Did you look at the Object Browser view in Visual Studio? In the top menu "View", then "Object Browser". I'm also working with COM libraries and use that look up the details, like types of parameters and return values. See here: learn.microsoft.com/en-us/visualstudio/ide/… — gdir
– gdir, Commented Oct 13, 2023 at 12:43

Daredevil · Accepted Answer · 2023-10-13 12:42:45Z

1

Visual Studio uses metadata to provide IntelliSense for COM objects, and that's how it's able to suggest properties and methods as you type. When a COM component is registered, type information is made available which development environments like Visual Studio can utilize.

However, when using COM interop from C#, especially with late binding, things can get a bit tricky. If you are accessing a COM object that does not have strongly-typed interop assemblies available (or if you are using late binding for some other reason), the result will often be a generic System.__ComObject, which does not provide much type information in C#.

I will recommend you use Type Libraries: If the COM component comes with a type library (.tlb file), you can import this into your C# project using the tlbimp.exe tool which comes with Visual Studio. This will generate a .NET interop assembly which provides strongly-typed classes for interacting with the COM component.

Or

Use dynamic: Starting from C# 4.0, you can use the dynamic keyword which effectively provides late binding in C#. This allows you to work with COM objects in a more VB-like manner:

dynamic app = GetComObject(); // Or however you get your COM object
var seats = app.Element.Car.seats;

answered Oct 13, 2023 at 12:42

Daredevil

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2 Comments

Simon Mourier Over a year ago

Sounds like AI generated answer. Not false, but quite irrelevant

Daredevil Over a year ago

Would like to understand how is it irrelevant? Questions were : Does Visual Studio somehow read the methods and properites that are available in the dll / library? And Is there any way to get the correct type and retrieve the actual value that is contained somehow in seats? Both the questions are answered and an additional hint provided.

Thomas Koelle · Accepted Answer · 2023-10-13 13:01:46Z

1

System.__Object and object is the same. If you have a library that returns objects then you can either assign them directly of if you don't want a runtime error typecast them yourself.

Excel interop is a good example. Here code could look like this:

int i = Convert.ToInt32(sheet.Range[$"A1"].Value),

If intelisense says objects just assume you have to do something yourself to cast it to whatever either hard or soft.

dynamic will always work. But for me it always gives more trouble than good.

answered Oct 13, 2023 at 13:01

Thomas Koelle

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