So Happy Together? Using ActiveX Components with Active Server Pages

Nancy Winnick Cluts
Developer Technology Engineer
Microsoft Corporation

November 19, 1997

The following article was originally published in the Site Builder Network Magazine.

After writing several articles about Active Server Pages (ASP) technology, I've heard from lots of people who are clamoring for more information. One of the most-requested subjects is the use of ActiveX™ components from ASP. Where can you find information about available components? What tools help you build components? Where can you find samples for building components?

When deciding whether to use an ActiveX component in your server application, keep a few things in mind:

The ActiveX component needs to provide a COM interface (See What is COM?, left) to communicate with your server application, other components, and your script.
The component should have no graphical user interface. If the component ran on the client machine, a graphical user interface would be fine; there's someone using the component who can interact with the interface. If, however, you are running a component on the server, you don't want message boxes popping up with no one to dismiss them. Instead, you want components that include business logic, such as parsing information, calculating some result, or gathering information.
A server component might be used in conjunction with a database to provide queries to the database or to parse through data received from the database. Let's say you have a Web site that provides information such as satellite or television programming. You could use an ActiveX server component to get the programming information from a database according to the user's time zone, programming preferences, and desired viewing time (for instance, it could return all comedies running in the Pacific time zone on Saturday night).
A server component could do complex calculations, such as determining a theoretical monthly mortgage payment given the price of the house, prevailing mortgage rates from several different banks, and discount points.

Once you decide that you are going to use an ActiveX server component, then decide whether you want to buy or to build the component yourself, and to what extent you can reuse the same code for other pages on your site.

The component can be written in any language: Visual Basic®, C++, Java, even FORTRAN! Any tool for any language that provides support for creating COM objects can be used to create an ActiveX component.

Reusing Components

Here in the soggy U.S. Pacific Northwest, recycling is very popular. Reuse of ActiveX server components fits well into this recycling life-style. The Internet Information Server (IIS) site offers many Active Server components you can download and use on your Web server. These components include the following:

The ASP To HTML (ASP2HTM) component can be passed a URL, and the object connects to the location and retrieves its properties. Once the properties are retrieved, the object can use them.
The Content Rotator component allows you to rotate through HTML content on a Web page. The component displays a new HTML content string each time a user requests the page, based on a content schedule file. The HTML content can be any type of content that HTML can represent: text, images, or hyperlinks.
The Summary Information component displays the properties of a document (or directory of documents).
The HTML Table Formatter component automatically converts data from an ADO Recordset object into an HTML-formatted table.
The Page Counter component counts and displays the number of times a Web page has been opened.
The Permission Checker component tests the Web user's access rights to a file or a page.
The Registry Access component provides access to the registry keys on a local or remote machine.
The Text Formatter component can be used to format text files for use in HTML <TEXTAREA> elements in browsers that do not wrap text in <TEXTAREA> elements for you.
The Tracer component is a lightweight profiler for ASP.

Along with the components listed above, you can also access some developer samples . These samples not only demonstrate the use of ASP components, but are also implemented in five different environments: Microsoft Visual C++®, using the Microsoft Active Template Library (ATL); Microsoft Visual C++, using Microsoft Foundation Classes (MFC); Microsoft Visual J++™; Microsoft Visual Basic version 4.0; and Microsoft Visual Basic version 5.0. This means you don't have to send me e-mail asking for the Visual Basic version; it's already there. Finally, you can check out the ASP Components Catalog for more components.

Building ActiveX Server Components

Okay, let's say that these reusable components don't do exactly what you need, and you've not found a component you can buy that fits your needs. You may need to build your own. There are several environments you can use to build your ActiveX server components.

Visual Basic Control Edition (version 5) : Ideal for Visual Basic developers. This environment provides the tools to build controls more rapidly than in other languages (such as C++), and supports Apartment model threading (the multiple-thread support used in Microsoft Internet Explorer 4.0).
Visual J++ : Allows you to write ActiveX server components using Java. This environment also supports Apartment Model threading.
Visual C++ : Use with MFC or with ATL to create ActiveX server components. If you already know MFC, and if you are already proficient with COM, you might want to choose MFC. If, on the other hand, you are a C or C++ developer with little COM experience, ATL is a better choice. Like the other tools mentioned, Visual C++ provides support for Apartment model threading.

Who You Gonna Ask? SBN Workshop

Once you decide what to build and which tool to use, you are probably going to look for specific tips for creating good server components. Luckily, our own Site Builder Workshop already has articles that:

Show how to develop Active Server Components with ATL
Provide ASP Troubleshooting Tips and Techniques
Provide Viewable Scripting Bug (this is a great source to keep you from banging your head against the wall when you come across a bug)
Explain Agility in Server Components (this tells how to make your component support both free- and Apartment-threaded models)

ActiveX Data Objects

ActiveX Data Objects (ADO) provide a collection of data access objects within an object library that enable you to write client applications that interact with databases. Those of you familiar with Data Access Objects (DAO) and Remote Data Objects (RDO) should find the programming model for ADO familiar. ActiveX server components can use ADO to work with databases to provide content based on user preferences, geographical data, or any other criterion.

You can use ADO on any operating system that supports COM and OLE automation (i.e.: 32-bit Windows environments). ADO is also language neutral: you can use it from C++, Java, Visual Basic, or any other language that supports COM and OLE automation.

To get started using ADO, check out the ADO Web site , and take a look there at an excerpt from the book Teach Yourself Active Web Database Programming in 21 Days . Reading it will give you a very good idea of just what ADO is and why it is so cool.

If you are going to use ADO, get familiar with the most commonly used ADO interfaces:

Connection: Provides a connection to a data source. By using the Execute method, you can run any king of command.
Command: Provides a method for sending a command that a data source can process. A command can be a simple SQL statement or calls to stored procedures in a database.
Parameter: Provides the ability to pass a parameter of a command.
Recordset: Provides cursor functionality.
Field: Provides a column in a Recordset that can be then used to retrieve or modify values in a column.
Error: Provides the means to return an error from a data source.

If you are already a proficient database developer, ADO shouldn't be difficult for you to use. It is well worth the time to learn about it if you are going to create a component that needs to interact with a database.

Still with Me?

If you've gotten this far, I can safely assume that you are still interested in writing ActiveX server components and using them with your ASP files. I encourage you to spend some time on the Microsoft IIS Web site to learn about ASP and the IIS environment. You can also check out the technical materials page on the Microsoft OLE DB site for further reading about databases and OLE (thrilling stuff ... really!).

Even as a little tyke, developer-technology writer Nancy Winnick Cluts was always the first one to raise her hand.

Get a grasp on ASP

Active Server Pages (ASP) technology provides a compile-free environment for creating server applications using any combination of HTML, scripting, and components. I've written several articles discussing the use of ASP, including an overview, tips, and general scripting. Others have written articles covering Web session management, creating ASP components, and debugging.

-- NWC

What is COM?

Component Object Model (COM) technology allows you to build applications from binary components that communicate together.

When you design an application to take advantage of COM, you pull out chunks of your code that stand alone in their functionality (for example, a specific set of functions that calculate a mortgage could go into a COM component).

These code chunks are implemented within executable (.exe) files or Dynamic Link Library (.dll) files. COM objects implemented in .dll files are called in-process servers, which can expose functions to outside applications. This means that other applications, even applications written by other companies, can call these exposed functions.

COM and ActiveX

ActiveX controls are implemented as COM objects. That's how ActiveX controls interoperate across networks, whether intranets or the Internet, and that's what allows the scripting of ActiveX controls.

When COM works across networks, it is called Distributed COM (DCOM). COM provides the aggregation (the way in which one object can make use of another object) for ActiveX. COM also provides the mechanism for packaging the parameters to functions (known as marshaling), so that those parameters can be passed across processes (and machines).

For technical how-to questions, check in with the Web Men Talking, the Site Builder Network's answer pair.