Microsoft’s .NET strategy does not leave Visual Basic 6.0
programmers completely in the dark. One of the benefits of .NET is the ease at
which you can create
Web services. Another benefit is its interoperability with Component Object
Model (COM), the basis for VB6 component creation and ActiveX.

VB6 programmers can find comfort in knowing that .NET
components can be registered as COM components, allowing VB6 programmers to
create a reference to the registered component and use that component within
their own projects. This can be a very powerful way to utilize .NET Web service
components within VB6 projects.

In this article, I will create a simple .NET Web service
component, as well as a client proxy for the service, and use that proxy within
VB6 without having to utilize the entire SOAP toolkit.

Creating Web services in .NET is simple, because the
foundation for HTTP transport through SOAP is built into the .NET Framework.
This is, for the most part, transparent to the .NET programmer. The .NET
programmer creates classes with public methods just like he/she would with any
other development environment. However, when he/she compiles the project, the
WSDL and supporting Web service functionality are created also. This is a major
benefit to creating applications in .NET.

Most likely, consumption of
.NET Web services is done through a consumer proxy. If you have the ASP.NET Web Matrix IDE on your PC, it
contains a tool for automatically creating these proxies. Otherwise, you can
create the proxy using command line tools available with the .NET Framework.
Once you’ve created these proxies, which include the source code, you can tweak
the code so that you can consume the proxy’s functionality as a registered COM
component in VB6.

Creating a solution

The first thing to do is create a .NET Web service
that provides simple functionality but is representative of a useful business
function that you would want to create as a Web service. Let’s create a service
for grabbing information from a database and supplying that data to the client.
This is what the great majority of all
business functions do. The proxy will consume the Web service and will be
registered as a COM component. Finally, a standard EXE will consume the proxy
COM and display the results in textboxes on a form.

The most common data you can find in most solutions is user
information. So in our .NET Web service, we’ll create a method that accepts an
integer value, the user ID as the parameter and returns a User type. The User
type contains members such as FirstName, LastName, etc.

First, create a .NET Web service application in the Visual
Studio .NET IDE, or you can create this solution in the ASP.NET Web Matrix IDE mentioned above. Add the code in
Listing A
to the newly created project.

From the preceding code, you can see where we create the
connection to the database (in this case, SQL Server), grab the user
information based on the user ID passed in to our method, and create and return
the User type.

Compile this code, and test the functionality by navigating
your browser to the URL where your Web service is located, such as
http://localhost/MyWebService/UserService.asmx. You should get a page that
lists the method of your service. Click on this method and you should get a
textbox to enter a user ID. Type in a valid user ID, click on
the Invoke button, and check the return information in the next page.
You should get XML back that looks something like
Listing B.

If you get this, then we’re on the right track. If not,
normal errors include security errors such as access to the database. In your web.config file, make sure the authentication type is set
to “Windows”, and add identity impersonation with the following code:

<authentication type="Windows" />
<identity impersonate="true" />

At this point, you may have to add IUSR_[computer
name] access to the database. You can add this user to the public role and
grant SELECT rights on your user information table to public. However, you
should turn off anonymous access to this page through Internet Services
Manager.

In the next article, I’ll create the Web service proxy using
both the command line tools and the Web Matrix IDE. I’ll tweak the code so that
it can be used as a COM component and rebuild the DLL. Then I’ll create a
standard VB6 EXE that will reference the proxy COM.

If you’re new to Web services in .NET, the ASP.NET Web site provides simple, yet effective,
information for creating Web services in .NET.

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