Passing array from .NET DLL to VB 6 application

Lets say we have a class library developed in .NET which returns an array of objects. When we use this .NET DLL in any VB 6 application an error throws saying “Type mismatch -error”. Even if the .NET DLL is registered for COM interop the error will throw while accessing array objects.

To resolve this issue we need to create a COM class in .NET. You can add a COM class to .NET project using Add->New Item->COM Class.

Here is an example showing usage of COM class.

[VB.NET CODE STARTS]

<ComClass(COMCLass1.ClassId, COMCLass1.InterfaceId, COMCLass1.EventsId)> _
Public Class COMCLass1
 
#Region "COM GUIDs"
    ' These  GUIDs provide the COM identity for this class
    ' and its COM interfaces. If you change them, existing
    ' clients will no longer be able to access the class.
    Public Const ClassId As String = "81960d64-b2fd-4344-9224-90376eb95d7a"
    Public Const InterfaceId As String = "621c203c-557a-49eb-814c-e67a8daa9376"
    Public Const EventsId As String = "2345b1c4-e95f-4d23-b007-dd276d349578"
#End Region
 
    ' A creatable COM class must have a Public Sub New()
    ' with no parameters, otherwise, the class will not be
    ' registered in the COM registry and cannot be created
    ' via CreateObject.
    Public Sub New()
        MyBase.New()
    End Sub
 
    Private _item As Integer
    Public Property Items() As Integer
        Get
            Return _item
        End Get
        Set(ByVal value As Integer)
            _item = value
        End Set
    End Property
 
End Class
 
<ComClass(COMCLass2.ClassId, COMCLass2.InterfaceId, COMCLass2.EventsId)> _
Public Class COMCLass2
 
#Region "COM GUIDs"
    ' These  GUIDs provide the COM identity for this class
    ' and its COM interfaces. If you change them, existing
    ' clients will no longer be able to access the class.
    Public Const ClassId As String = "bd0ae776-0df4-43ab-bb17-bd51d9cfa69f"
    Public Const InterfaceId As String = "9845f800-6bce-4a78-9f24-e263d7d47e74"
    Public Const EventsId As String = "7be9b049-1952-416a-9474-72cb5e17534d"
#End Region
 
    ' A creatable COM class must have a Public Sub New()
    ' with no parameters, otherwise, the class will not be
    ' registered in the COM registry and cannot be created
    ' via CreateObject.
    Public Sub New()
        MyBase.New()
    End Sub
 
    Private items() As COMCLass1
 
    
    Public Function GetItemArray() As COMCLass1
 
       ReDim items(1)
 
        items(0) = New ComClass1   
        items(1) = New ComClass1   
        items(0).Items = 1   
        items(1).Items = 2  
 
        Return items  
 
    End Function
 
End Class

[VB.NET CODE ENDS]

Add the reference of .NET DLL in VB 6.

[VB 6 CODE STARTS]

Dim comObj As COMCLass2
Set comObj = New COMCLass2
Dim comObj2() As COMCLass1
 
comObj2 = comObj.GetItemArray()
 
Dim i As Integer
 
For i = 0 To Unbound(comObj2)
   ' get each value
Next

[VB 6 CODE ENDS]

This way we can pass array objects from .NET to VB 6 application.