Special Edition Using Visual Basic Script kkvbsfi.htm




- Special Edition Using Visual Basic Script -


Appendix D - Porting Visual Basic Applications




When VBScript first appeared on the scene, it seemed unlikely that any
effort to port VB programs to VBS scripts was even remotely feasible. Even
apart from language limitations (such as no file I/O, no Typed structures,
no Class modules, no Collections, and so on), the overriding reality was
that VBS "applications" were HTML-bound. As has oft been noted,
HTML, basically an upper-left to lower-right text-flow formatter, is ill-suited
in situations that vector off from its original mission.

The recent appearance of HTML Layout Page functionality, combined with
the productivity-enhancing ActiveX Control Pad have changed this assessment
to the degree that it is no longer unthinkable to port some VB applications
to the Web.

If you are willing to do a fair amount of work dealing with the limitations
and differences that remain, you will be able to bring certain VB applications
to VBScript. At the very least, you should be able to duplicate most, if
not all, of your user interface elements. Even so, there are some show-stoppers
you need to be aware of from the start. If your program depends on any
of them, you'll need to seriously consider whether you want to proceed.

Considering a Few Caveats

HTML Layout Pages, for all their similarity to VB Forms, are severely
lacking in terms of properties, methods, events, and behavior. Essentially,
they are dumb containers of controls; if you need to do anything at the
form level (VB form, not HTML form), it won't happen, at least at this
stage of the game. This includes such things as using the Print method
to place text directly on a form, graphics methods (Line, Circle, and so
on) to draw on a form, hiding, showing, or unloading a form, and trapping
any events (such as mouse clicks or keystrokes).

You won't be able to do anything with Typed records. You may be able
to get around this limitation by using multi-dimensional arrays, or, groups
of arrays. You can't create Collections. Again, you may be able to use
arrays this was SOP prior to VB4, so it's definitely within the realm of
"doability."

Class modules don't exist in VBScript. Nor, for that matter, do standard
.BAS modules. You can deal with the latter omission by placing your procedures
in the same file as your controls, or the HTML file that holds points to
it. (At the time this book goes to press, HTML Layout Pages must reside
in .ALX files, and an <OBJECT...> reference to the .ALX file must
be placed in an HTML file. Microsoft has announced that when IE 3.0 is
released, it is expected to support the use of HTML Layout Pages within
an .HTM page.) As to Class modules, you may be able to duplicate their
functionality by using procedures. Clearly, if you have a heavy investment
in Class modules that you want to port over to Web applications, it may
be in your interest to wait a while. See "Sweeping the Horizon,"
in this appendix for what may be a glimmer of hope.

Other features that you're "protected" from include the Printer
Object, communications ports, and API (or other .DLL) calls.

File I/O is a real problem. You can write Class wrappers in VB4,
and compile them to in-process .DLLs (for information on this topic, check
out Que's "Special Edition Using VB4"), but, you should
realize that it's an exercise that's not for the faint of heart. In addition
to heavy VB coding, you'll need to embed <OBJECT> tags at the HTML
level, using ClassID references, and at this time, it's impossible to use
them with HTML Layout Pages, as the ActiveX Control Pad won't work with
anything that doesn't meet the new ActiveX qualifications.

If you get that far, you'll still be faced with a security issue. The
creators of the Internet Explorer have not simply relied on VBScript's
lack of native file I/O for protection from malicious programmers. Attempting
to use an object that does not contain a valid digital signature from a
certificate agency, will result in warning boxes being displayed each time
the page is loaded, unless security in the Internet Explorer is shut down.
Shutting down security is definitely not recommended unless you
are absolutely certain that the browsers in question will never
wander off the safety of a corporate Intranet.

Sweeping the Horizon

If you do require language and/or object functionality that is not available
in VBScript, you should remember that VBScript, VB, Internet Explorer,
Windows, and even the Internet, are all moving targets. The only time something
stands still is when it's dead in the water. It's not unreasonable to hope
that later versions of the platform will include functionality that is
missing now. Right now, VBScript is in its first generation. Windows is
poised to undergo a major transformation, as the desktop blends into the
Internet. No one outside the inner sanctums at Microsoft can say exactly
where things will end up, although we do know that in general, we'll
be getting better tools, more robust language implementations, and easier
means for accomplishing tasks.

Microsoft has been dropping teasers in the press regarding the next
major release of Visual Basic. Some of what they've publicly made known
has a direct bearing on the things you'll be doing with VBScript and HTML
Layout Pages.

For instance, you'll be able to write your own ActiveX controls, and
roll in whatever functionality you require. Because Visual Basic is a full-featured
language, this means that you should be able to supply much of the functionality
that is currently missing from VBScript.

In the majority of cases, if you have a VB application that you want
to port to VBS, you'll be looking at a complete rewrite. You should, however,
be able to preserve the "look and feel" of your applications,
assuming you can avoid use of graphics methods and form events. Many specific
procedures, and much of your existing event code routines, can be carried
over to VBScript, in some cases with little or no change. However, the
structural aspects of your code Modules, Classes, and data structures will
need to be redesigned, or rewritten.

If, after you assess the situation, you realize that the law of diminishing
returns has been invoked, you'll need to make the hard choice to either
scrap the project, or come up with a workable alternative. No amount of
advice or counsel can protect you from situations like this, and although
they test your mettle, they can also provide opportunity. Take the resources
at hand, reason out the situation, and present a solution. That's what
sets you apart from the pack.