ERCB: ActiveX Development with Visual Basic 5

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Title	ActiveX Development with Visual Basic 5: The Professional Guide to Programming Internet/Intranet Applications
Author	Evangelos Petroutsosis
Publisher	Ventana Press http://www.vmedia.com
Copyright	1997
ISBN	1-566-0-4648-3
Pages	548
Price	$49.99

ActiveX Development with Visual Basic 5

ActiveX Development with Visual Basic 5 is targeted at programmers with some proficiency in Microsoft Visual Basic who have a need to customize ActiveX controls, or write completely new ones, and who want to learn something about programming for the World Wide Web. Readers should also have a copy of VB5, since most of the programming examples make heavy use of that toolset. As the subtitle indicates, ActiveX Development with Visual Basic 5 is primarily concerned with Internet/intranet applications. The first third of the book provides a good introduction to HTML and VBScript, with enough examples and explanation to enable you to develop just about any client-side web page application, including among the standard capabilities:

Image maps to turn on-screen images into hyperlinks.
Inputting data with standard controls (the seven intrinsic to HTML plus several more from VBScript).
Use of layout and script editors from Visual Basic.
Use of VBScript for validating input data.
Creating and extracting cookies.

There is also some discussion of the subtleties such as simulating an irregularly shaped graphics object on the screen, in spite of the HTML restriction that IMG objects be rectangular, and using a For...Next loop to create a color cycle, which can provide the effect of a picture fading into view, rather than simply popping onto the screen. The last third of this book provides an introduction to communications on the Internet, particularly the Web and more specifically how these chores are handled by the Microsoft web servers: Personal Web Server for Windows 95 and the much more capable Internet Information Server (IIS) for Windows NT. Standard server topics include:

IP addresses.
The Internet Service Manager (ISM, available only with IIS).
Setting up an ODBC (Open Database Connectivity) database.
Servicing client requests for information from databases (using Internet Database Connector (IDC) files to process SQL queries and HTX files with HTML extensions to format the response).
ActiveX components and their use for parsing client data input strings.
Active Server Pages which reside on the server but specify a flexible partitioning of any of the above data manipulation tasks between client and server.

The middle third of the book is where you'll be told about the subject most prominently featured in the title: development with, and of, ActiveX controls. Within this limited space, Petroutsosis still manages to cover the territory by heavily emphasizing "how", with the aid of the extensive Visual Basic toolset, and largely neglecting "why." Some of the examples primarily concern control functionality:

A web browser control.
An HTML editor and renderer.
A Winsock control for communication between computers (which, in turn, is applied to the more specific functions of a "chat" and two- person game playing).
The TabStrip control which facilitates the dividing of your web project into a sequence of tabbed pages, each containing the same controls (controls created with Visual C++ or Delphi can have different controls on different pages) and presenting, or accepting, related data in each.
The Marquee control (which provides eye- catching animation of your banner, but which has been found not very useful in recent user surveys: not surprising to those of us who remember that marquees have been abandoned by movie theatres years ago).

Most of the control examples, however, primarily concern the ActiveX features:

Providing the capability for a developer to manipulate properties in a design environment (which is really provided by the ActiveX wrapper for an ordinary control, VBX in Visual Basic or VCL in Delphi).
Automatic downloading and use by a client without any specific installation required.

The property manipulation features include:

Addition of custom properties in the design environment.
Setting property values in code by the author, in property sheets by the designer, or in dialog/input boxes by the end user at run time.
Use of the PropertyBag object to save property values between design time and run time.
Specification of an enumerated set of possible values for a custom parameter and their automatic incorporation into the property sheet.

ActiveX automatic downloading and client usability examples include: (1) downloading properties and content (particularly graphics) with the control's AsyncRead method, (2) code developed by the Application Setup Wizard to register the control and obtain a CLASSID (both for the new custom control and any common subsidiary controls used, which will enable the client system to avoid installing multiple instances of such common controls), (3) the cabinet file (.CAB) to compress and package all data to be downloaded (not only the controls but also instr uctions to the client system on what to do with them), (4) digital signature/authentication. The CD-ROM contains complete code for all the examples, which can serve as templates for a variety of useful tasks.

Deficiencies:

No comprehensive controls reference, or much guidance on how to use the MSVB online help (which is essential because Microsoft, like many vendors, no longer gives printed manuals).
Thirty-six pages devoted to ActiveX documents without ever providing a practical example of their usefulness.
At least six mistakes in the text and/or incorrect figures.
Although object terminology is used throughout, there is no coherent discussion of the object model, just properties and methods, and there is no mention of COM at all.
Poor discussion of .CAB files which does not even mention DDF and INF files.
No discussion of design time licensing.

The last three of these are perhaps the price paid for the environment which has all properties laid out at once in sheets in a special window. It's too bad that the property sheets may be of diminishing use now that tabbed property pages are becomming the vogue.

-- Peter Gottlieb (Peter_Gottlieb@notes.ymp.gov)

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