.net components in com, DOT NET Programming

How can we use .NET components in COM

.NET components can't be used in straight forward way with the COM. You will require to create CCW in order to communicate COM components  with .NET assemblies. Following are some of the different approaches to implement it :-

1)Explicitly declare interfaces

Public Interface ICustomer

Property CustomerName() As String

Property CustomerCode() As String

Sub AddCustomer()

 End Interface

Public Class Customer

 Implements ICustomer

Private PstrCustomerName As String

Private PstrCustomerCode As String

Public Sub AddCustomer() Implements ICustomer.AddCustomer Try

 ' addin of database code can go here

Catch ex As Exception

Throw ex

 End Try

End Sub

Public Property CustomerCode() As String Implements



 Return PstrCustomerCode

 End Get

Set(ByVal value As String)

PstrCustomerCode = value

End Set

End Property

Public Property CustomerName() As String Implements ICustomer.CustomerName


Return PstrCustomerName

 End Get

Set(ByVal value As String) PstrCustomerName = value

End Set

End Property

 Public Sub New()

End Sub

End Class

The above customer class is going to be used by COM components so all the properties and methods are declared in interface and implemented in the customer class.Customer Name.Customer Code &  AddCustomer are Ist declared in ICustomer & then implemented in the Customer Class. Please Note that the class must have a default constructor.

2)The second way to generate  CCW is by using InteropServices attributes. In this interfaces are created automatically.

 Following are the different type of class attributes :

None:-No class interface is generated for  class. This is the default setting when you do not specify anything.

AutoDispatch :- Interface that supports IDispatch is created for class. However, no type information is generated.

AutoDual :- A dual interface is created for the class. Type information is generated and made available in the type library.

Below are the source code we have used the third attribute.

Imports System.Runtime.InteropServices

  _ Public Class ClsCompliant

End Class

Other than class attributes defined up there are some other attributes with which you can govern other part of  the assembly. For Example "GuidAttribute" allows you to specify the GUID, "ComVisibleAttribute" can be used to hide .NET types from COM etc.

a)When  .NET assembly is created using either interface or by using interopservices method we need to create a COM type library using Type library export tool.

Tlbexp (AssemblyName)

b)The final thing is registering the CCW in registry by using regasm tool.

regasm AssemblyName [Options]

c)Finally refer the TLB in your COM IDE Below is figure showing VB6 IDE referencing the DLL

500_.NET components in COM.png

Posted Date: 9/21/2012 7:23:35 AM | Location : United States

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