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ComClassAttribute Class

The ComClassAttribute attribute instructs the compiler to add metadata that allows a class to be exposed as a COM object.

Namespace:  Microsoft.VisualBasic
Assembly:  Microsoft.VisualBasic (in Microsoft.VisualBasic.dll)

[AttributeUsageAttribute(AttributeTargets.Class, Inherited = false, AllowMultiple = false)]
public sealed class ComClassAttribute : Attribute

For more detailed information, see the Visual Basic topic ComClassAttribute Class.

Use ComClassAttribute to simplify the process of exposing COM components from Visual Basic. COM objects are very different from .NET Framework assemblies; without the ComClassAttribute, you need to follow a number of steps to generate a COM object from Visual Basic. For classes marked with ComClassAttribute, the compiler performs many of these steps automatically.


This attribute simplifies the creation of COM objects. To expose a class as a COM object, you must compile the project with the Register for COM Interop option selected in the Build section of the Configuration Properties dialog box.


Although you can also expose a class created with Visual Basic as a COM object for unmanaged code to use, it is not a true COM object. For details, see COM Interoperability in .NET Framework Applications.

To run this example, create a new Class Library application and add the following code to a class module.

    <ComClass(ComClass1.ClassId, ComClass1.InterfaceId, ComClass1.EventsId)> _
    Public Class ComClass1
        ' Use the Region directive to define a section named COM Guids. 
#Region "COM GUIDs" 
        ' These  GUIDs provide the COM identity for this class  
        ' and its COM interfaces. You can generate  
        ' these guids using guidgen.exe 
        Public Const ClassId As String = "7666AC25-855F-4534-BC55-27BF09D49D46" 
        Public Const InterfaceId As String = "54388137-8A76-491e-AA3A-853E23AC1217" 
        Public Const EventsId As String = "EA329A13-16A0-478d-B41F-47583A761FF2"
#End Region

        Public Sub New()
        End Sub 

        Function AddNumbers(ByVal X As Integer, ByVal Y As Integer)
            AddNumbers = X + Y
        End Function 
    End Class


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0