Home   |   QuickStart Welcome   |   ASP.NET   |   Web Services   |   How Do I...?   
  |   I want my samples in...      

How Do I...? Common Tasks QuickStart Tutorial

How Do I...Pass Simple Data from .NET Code to VB6 code?

This example demonstrates how to use .NET objects from a Visual Basic 6.0 application. The same technique can be used to create the object from any COM application, including those built with Visual C++ 6.0, VBScript, or JScript.

In this example, a very simple class called Test implements the ITest interface. This interface has a single method that returns the current time and can be easily used from COM. It is possible to avoid an explicit definition of interface and use class interface, which contains all of the members of the class and all the members of its base classes. This technique is available by applying the DefaultInterface.AutoDual attribute but is strongly discouraged because it seriously limits your ability to version your classes.

namespace TestServer{
	public interface ITest{
		DateTime GetTime();

	public class Test : ITest{
		DateTime ITest.GetTime(){
			return DateTime.Now;

After compiling the managed code to create the TestServer assembly, the assembly must be installed in the global assembly cache (GAC) and registered for use from COM. Use gacutil.exe to install the TestServer assembly in the GAC and add the registry entries needed to make the types within the assembly creatable from COM.

gacutil /i TestServer.dll

In order to use the types defined within the TestServer assembly from Visual Basic 6.0, it helps to have a type library that describes the types contained in the assembly. Use tlbexp.exe to produce a type library from any managed assembly or check the option in the Build Project settings to "Register for COM Interop".

tlbexp TestServer.dll

The type library produced by tlbexp.exe can then be added to the project through the Project/Reference dialog in Visual Basic 6.0. Once the reference to the type library is added to the project, the types defined in the assembly can be referenced directly within the Visual Basic code.

Dim dotNETServer As TestServer.ITest
Set dotNETServer = New TestServer.Test

Debug.Print ".NET server returned: " + FormatDateTime(dotNETServer.GetTime, vbGeneralDate)

In order to run the application, the assembly is typically installed in the global assembly cache as described above. During development, it is easier to simply copy the assembly to the application directory. Assemblies can only be located if they reside in the application directory or in the global assembly cache.

Note: If you are trying to run the application from within the Visual Basic 6.0 development environment, the assembly must be in the same directory as vb6.exe because vb6.exe is the process hosting the assembly.

VB Test Client
View Source
[This sample can be found at C:\DevFusion.Data\legacy\quickstart.developerfusion.co.uk\QuickStart\howto\samples\Interop\TestServer_1\]

Microsoft .NET Framework SDK QuickStart Tutorials Version 2.0
Copyright � 2004 Microsoft Corporation. All rights reserved.