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Accessing COM+ component using C#

, 30 Oct 2001
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This article provides a step by step explanation on how to access COM+ applications using C#.


This article explains step by step of accessing COM+ application using C#. The code is compiled using beta2. Microsoft (R) Visual C# Compiler Version 7.00.9254 [CLR version v1.0.2914]. It can be used with Beta1 with some minor modification.

If we want need to access the existing COM+ application with any .net supported language, we don't need to modify the single line of existing COM+ application, despite of the fact their execution model is completely different. Here is the step-by-step easy example of doing the same. We can access it in two ways, Early Binding and Late binding (remembered the old VB concepts). We will first look at Early binding example...

Early Binding

Tools Required

TlbImp.exe: (Type Library Importer) Imports (converts, generates wrapper DLL) the type definition found in COM component into equivalent .net definitions (or metadata), understandable by Common Language Runtime (CLR). The metadata generated, by TlbImp can be viewed by Ildasm.exe. If you are using the Visual Studio development environment, you only need to add a reference to the COM type library and the conversion is done automatically.

Let's Start

To use existing COM+ application we need create Runtime Callable Wrapper (RCW) using TlbImp.Exe, with VS.Net it is created automatically, when we reference the existing COM Component. The difference is that, VS.Net create the RCW with the same name as the original DLL, which may be confusing, and with TlbImp.Exe, we can specify the different name using /out: parameter.

Let us assume that we have a COM Component with a method Add, which takes two parameter A and B and returns the Sum.

Note: We have to register COM DLL first before using it...
Public Function Add(A As Long, B As Long) As Long

    Add = A + B

End Function

Now we will run TlbImp.Exe in our existing DLL i.e. CompAdd.Dll

This generated a wrapper dll CompAddRcw.dll. we can view this DLL using IlDasm.Exe

The discussion in IlDasm.Exe is beyond the scope of this article. Now we will simply write code to use the Wrapper DLL, which in turn will be calling the actual DLL. Now let us look into the C# code for doing it.

As we can see that we are getting the same kind of tooltip as we used to get with VB when we do early binding. Compile the program with /r: switch TestClient.cs /r:CompAddRcw.dll. Execute it and we just called COM component with .net.

Late Binding

For Late binding we have to use System.Reflection namespace, which allows us to programmatically access the types contained in any assembly. We will see how we can do late bindings in four easy steps..
  • We have Get IDispatch Interface using Type.GetTypeFromProgID("Project1.Class1")
  • We have to create instance using the type ID Activator.CreateInstance(objAddType)
  • We have to make array of arguments (if required)
  • Invoke the Method using objAddType.InvokeMember function.


The method Type.GetTypeFromProgID is used to load the type information of the COM object. The call to Activator.CreateInstance returns an instance of the COM object. And Finally InvokeMember function is used to call the Method of COM object.


This article gives very basic idea of using the old COM Application, for the purpose of simplicity and to focus on the purpose of the article no error handling has been done. In my next article we will see how can we use .NET component with VB.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

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About the Author

Imtiaz Alam

United States United States
No Biography provided

Comments and Discussions

Generalvalue cannot be null. Pinmemberjimkqui25-Sep-08 20:54 
GeneralRe: value cannot be null. Pinmemberjjjkkk26-Sep-08 0:47 
GeneralCOM Exception Pinmemberandrojdaz27-May-08 21:35 
GeneralRe: COM Exception PinmemberKipetcoff6-Aug-08 7:38 
I have the same error.. try to register this dll. Regsvr32.exe
GeneralRe: COM Exception Pinmemberjimkqui25-Sep-08 20:54 
QuestionWhat about calling COM+ on another server? PinmemberDan Vallejo10-Oct-07 7:38 
AnswerRe: What about calling COM+ on another server? Pinmemberjjjkkk26-Sep-08 13:40 
GeneralRe: What about calling COM+ on another server? Pinmemberejojart20-Mar-09 6:07 
GeneralThank you PinmemberHez26-Apr-06 1:50 
GeneralNeed help! Pinmemberlily0lin11-Oct-05 7:51 
GeneralRe: Need help! Pinmemberjimkqui25-Sep-08 20:56 
GeneralSimple and Concise Pinmembermcintyak7-Oct-05 18:36 
QuestionWhy was this dumb article written ? PinmemberAnonymous19-Feb-02 22:02 
AnswerFor people to learn I guess :-) PinmemberAnnie.586F988F-563B-41f5-8B46-0EB4ADB8B8EE2-Jul-02 1:54 
AnswerRe: Why was this dumb article written ? PinmemberJamie Nordmeyer16-Dec-02 10:45 
GeneralThis is a dumb article PinsussAkshay Zadgaonkar11-Jun-03 0:12 
GeneralRe: This is a dumb article Pinmembernormanzb19-Sep-07 23:20 
AnswerRe: Why was this dumb article written ? Pinmemberxavitomorera16-Jun-04 15:11 

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