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Web Database Developer's Guide with Visual Basic 5

World Wide Web Database Developer's Guide with Visual Basic 5



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ActiveX and ActiveX Controls

The incorporation of <OBJECT>s in HTML 3.2 signaled the beginning of a new era in Web applications development. That might sound like a strong statement, but think about it for a moment. The <OBJECT> tag enables developers to incorporate virtually any object into a Web page. As a result, the possible ways to expand the functionality and interactiveness of your Web pages is becoming limited more by a developer's imagination than by technological barriers.



As you will begin to see in this chapter and later chapters, one of the easiest yet most powerful ways to extend the functionality of your Web applications is by using ActiveX technologies in general and ActiveX controls in particular. ActiveX controls are complex objects that can be inserted into your Web pages and manipulated and controlled by using VBScript. By using HTML <OBJECT>s and ActiveX controls with VBScript, developers quickly can incorporate components that suit their needs and build the type of powerful client-side applications that until just recently were simply not technologically possible.

What Is ActiveX?

ActiveX isn't any single thing; it is a set of new technologies unveiled by Microsoft in early 1996. Simply stated, ActiveX is a language-neutral set of integration technologies that enable software components to work together in a networked environment. This means that, regardless of the language used for development, the components still interoperate and communicate properly. ActiveX defines the packaging of software components and how those components should communicate. As a result, ActiveX components can be

These qualities of ActiveX enable developers to easily create interactive applications and Websites using an open development framework.

The set of ActiveX technologies forms a framework for creating interactive Web content through the use of software components, scripts, and existing applications. Specifically, ActiveX technologies enable content providers and applications developers to easily create dynamic Web content and Web server extensions by using ActiveX controls, active scripting, and active document interfaces. You will learn more about these elements later in this chapter.

Why Use ActiveX?

Perhaps a better question would be, "Why wouldn't you use ActiveX?" This is a question for which we don't have a good answer. ActiveX simply enables developers to do too many good things to ignore. Consider these capabilities:

ActiveX Background and History

ActiveX is the result of a natural evolution and growth of existing Microsoft technologies. These technologies include the following controls:

VBXs and OCXs enable you to quickly and easily expand the function of a program simply by inserting these components into your program to add needed functionality. As a result, the power of your programs can be expanded quickly, easily, and reliably by taking advantage of the communications, control, and functionality provided by these controls.

Because OCX technology is such a powerful programming model, it was only a matter of time before it was applied to Web applications development using rapidly maturing scripting languages such as VBScript. Technologically, however, an impediment still existed to fully applying this model to Web applications development. The steady evolution of controls in the Windows environment resulted in technologies that were somewhat bloated and platform specific:

These problems were contrary to what was needed for controls that could be used on the Web:

Microsoft addressed these needs by taking the best portions of OCX technologies and adding to them.

The resultant set of technologies was named ActiveX. Along the way, it was broadened significantly to incorporate not only ActiveX (formerly OCX) controls, but other technologies, such as active scripting and active documents central to Microsoft's Internet strategy.

ActiveX technologies are centered on the concept of treating applications, as well as traditional Web pages, as active documents that can be hosted in an all-encompassing shell. The idea is that the next generation Web browser will be capable of hosting nearly all interactions with the computer. In effect, the wide chasm that currently exists between operating system and browser will become much smaller as they are merged (at least in the Windows environment).

The Component Object Model (COM)

The Component Object Model (COM) is a client/server, object-based model that is the basic technical foundation cornerstone for ActiveX components. The model is designed to enable software components and applications to interact, even across networks, in a standard and uniform way. The COM standard is really partly a specification and partly an implementation:

Some characteristics of COM follow:

RESOURCE: You can find additional information, as well as complete COM and DCOM specifications, on Microsoft's OLE Development Website at 
http://www.microsoft.com/oledev/





How COM Works


As stated previously, COM is a client/server-based model. When a client object
wants to use the services provided by a server COM object, it uses one of the core
services that are part of the COM library. The COM library is responsible for creating
the server COM object and then establishing an initial connection between the client
and server objects.


The connection is considered established when the server object returns a pointer
to the client. This pointer points to an interface in the server object. The COM
library now has completed its role in the process and leaves the objects to communicate
directly with one another.


COM objects use interfaces to communicate with one another. An interface is a
set of related functions that provide some sort of required services. Interfaces
are language-independent. Any language capable of creating structures of pointers,
as well as calling functions via pointers, can be used to implement COM interfaces.


COM objects can have multiple interfaces. After a client object obtains a pointer
to a server object's interface, the client can invoke any of the functions or services
provided by that interface. After an object finishes using services provided by the
server object, the client simply informs the server that it is all done and terminates
the connection between the two.

What Is a COM Interface?


COM interfaces are small sets of language-independent functions that are related
in some way--logically or semantically. These interfaces provide the mechanism by
which server objects make services available to client objects.


COM interfaces are given unique names by using globally unique identifiers (GUIDs).
These identifiers are 128-bit numbers that are used to avoid name clashes that easily
could occur by using human-readable names. GUIDs are guaranteed to be (nearly) unique
by the COM specification. This specification indicates that 10 million GUIDs per
second could be generated over the next 3,500 years (approximately) and that each
of these GUIDs would be unique. This is unlikely to be the case with any human-readable
form of naming.


COM server objects can supply more than one type of service; a separate interface
is provided for each service. When a client object obtains a pointer from the server,
it provides access only to the services provided by that specific interface. Clients
can obtain pointers to other server interfaces through the IUnknown interface.
IUnknown is a fundamental interface through which all other interfaces are
derived, and it must be supported by all COM objects.


The IUnknown interface has a function called QueryInterface.
Because all interfaces are derived from IUnknown, this function is present
in all interfaces. QueryInterface has knowledge of all interfaces in the
server object and therefore can provide a client with a pointer to any server interface
to which it requires access.

COM Server Object
Types


COM specifies three types of server objects:





Regardless of where a server object is running (locally or remote), client objects
always communicate with it in the same way. A client object accesses the services
provided by a server object via a pointer to an interface on the server. For servers
running in-process, the pointer can access the interface directly. For servers running
locally or remotely, however, the pointer accesses a COM-supplied proxy server running
in the same process space as the client. The proxy then generates a call to the local
or remote server object on behalf of the client. COM server objects use a stub object
supplied by COM. This stub receives calls from client objects and translates these
to calls on the appropriate interface.

COM Foundation Components


COM primarily is concerned with the business of creating objects and facilitating
standard communication between those objects. However, COM also provides a few other
fundamental system-level objects:





The ActiveX Object
Model


The ActiveX Object Model consists of the following two pieces, both of which are
in-process (DLL-based) COM types:





All interfaces defined in the ActiveX Object Model are dual interfaces. In dual
interfaces, the objects inherit and follow some simple rules. Therefore, they can
be used by late-bind OLE Automation controllers (through the use of IDispatch::GetIdsOfNames
and IDispatch::Invoke). They also can be used by early-bind controllers
(for example, using a vtable).

The MSHTML Viewer
Component


MSHTML is the HTML viewer part of the Microsoft Internet Explorer 3.0 (IE 3.0)
browser. It can be hosted in both OLE document object containers and OLE control
containers. It also can be used as a standalone OLE Automation component.


MSHTML implements the OLE Automation Object Model described by the HTML Scripting
Object Model. With this object model, you can develop rich, interactive, multimedia
HTML content. Client-side scripts (such as VBScript running in the browser), as well
as externally running programs (such as VB 4 and VB 5), can use the object model.

The IExplorer Browser
Object


The IExplorer Browser object is an in-process COM server. The IExplorer Browser
is the core of what users see when using Internet Explorer 3.0. The Browser object
also is a document object container. This container can host any document objects
(such as Word, Excel, and even HTML) with the added benefit that it fully supports
hyperlinks to any document type. Because it is a COM class object that implements
all the interfaces needed to be used as an OLE control, the IExplorer Browser is
itself an OLE control.


The IExplorer's IShellExplorer interface is the primary OLE Automation-compatible
interface exposed by the IExplorer Browser OLE control. The IInternetExplorer
interface is a superset of the IShellExplorer interface. It can be contained
within any OLE control container, such as Internet Explorer 3.0, which raises some
interesting possibilities. Imagine the added functionality you could give users by
enabling them to embed and control a browser from within your Web applications (a
browser-within-a-browser) as well as your VB applications.

ActiveX Controls


ActiveX controls are reusable software components developed by software vendors
as well as VB developers like yourself. You easily can add these controls to Web
pages by using the <OBJECT> tag. When used with VBScript, these controls
can dramatically increase the interactiveness, functionality, and usefulness of your
Website.


Straight COM objects combined with a few ActiveX interfaces can become Internet-enabled
without modifying the existing object. You can create ActiveX controls from a variety
of existing object types, such as the following:





ActiveX controls provide a means of instantly adding new and dynamic functions
to Web applications. These controls are the building blocks for client- or server-driven
dynamic content. Controls exist that enable you to integrate virtually any media
type (such as sound, video, animation, interactive input devices, and so on) into
your Web applications. Later sections of this chapter and subsequent chapters present
a variety of controls that you easily can obtain and implement rapidly. The use of
these controls will be demonstrated in several examples.

ActiveX Scripting
Services


ActiveX scripting defines a syntax- and language-independent architecture that
enables you to add scripting and OLE Automation capabilities to programs. ActiveX
scripting provides the necessary platform for developing script engines.


ActiveX scripting components can be grouped into two major categories:





ActiveX Documents


ActiveX documents are based on OLE document objects (DocObjects). The
DocObjects technology is a set of extensions to OLE documents; it is the
compound document technology provided by OLE. Documents that conform to the ActiveX
standard can be opened within ActiveX document containers. In other words, they can
be viewed within Internet Explorer 3.0. Documents that conform to the ActiveX standard
follow:





Note that Binder is a sophisticated viewer capable of hosting a variety of documents
so that you can create, edit, save, print, and view different kinds of information
collectively. Internet browsers (such as IE 3) that adopt Binder technology not only
facilitate the presentation of Internet-based information (such as HTML-based Web
pages), but they also enable the browser to present documents from Microsoft Office
and Microsoft Office-compatible applications. In the future, you will be able to
view, navigate, and distribute virtually any document type (whether it is local or
remote) by using browsers that adhere to ActiveX and DocObject container
standards.

The ActiveX Server
Framework


The ActiveX Server framework is based on the Microsoft Internet Information Server
(IIS), which is an integrated component of Windows NT Server. The framework enables
Web developers to take advantage of the powerful Microsoft BackOffice suite of products
(which includes Microsoft SQL Server and Microsoft Exchange Server). The ActiveX
Server framework consists of ActiveX Server scripting and ActiveX Server controls.
ActiveX Server scripting can be written with any scripting language, including VBScript,
Perl, C, or JavaScript. The CGI also is supported under the ActiveX Server framework.
Through CGI, you can extend the functionality of your Web applications by giving
clients access to services (such as databases) that they ordinarily would not be
able to access.

Using ActiveX Controls
in Your Applications


Remember that ActiveX controls enable you to rapidly improve the quality and functionality
of your Web applications simply by embedding prepackaged objects in your Web pages.
By adding VBScript programs to control these objects and handle various events, you
can develop interactive and highly functional client-side applications that simply
were not possible before. This section presents a few basics on using objects in
your applications. Examples in later chapters discuss using ActiveX controls in greater
detail.


Three primary sources exist for ActiveX controls. Microsoft provides many ActiveX
controls with IE and a development tool called the ActiveX Control Pad. Table 13.1
summarizes these controls. Third-party vendors produce a dazzling number of ActiveX
controls designed to perform specific tasks. Note that the control you need often
already exists and can be cheaper to purchase than to write, debug, and maintain
yourself. The third source for controls is you (and other benevolent developers who
make their controls freely available on the Internet). Why would you write an ActiveX
control? Sometimes you want to integrate some type of functionality into your program,
but you cannot locate a control on the market that adequately meets your needs. In
these cases, you have to do it yourself. Fortunately, VB 5 and VB 5 Control Creation
Edition provide everything you need (including control-creation wizards) to develop
your own controls.



	



RESOURCE: Although Microsoft has hinted that
	ActiveX will make its way into the UNIX world, ActiveX technologies currently are
	geared primarily toward the Microsoft environment. Internet Explorer 3.0 currently
	is the only Web browser that offers native support for ActiveX. NCompass Labs, however,
	has developed plug-ins for Netscape Navigator that provide the capability to use
	ActiveX controls, VBScript, and ActiveX documents with Navigator.







	
You can find more information on NCompass Labs and trial downloads at

	
http://www.ncompasslabs.com/

	










Controls Available
with IE 3.0 and the ActiveX Control Pad


An increasing number of ActiveX controls are available for developers to use in
their Web applications. Although a good number of these must be purchased from third-party
vendors, Microsoft provides free a fair number of controls. Table 13.1 outlines those
controls that ship with IE 3.0 and the ActiveX Control Pad. 



Table 13.1. Standard ActiveX Controls that Ship with Internet Explorer
and the ActiveX Control Pad. 


	

		Control
		Function
	








	

		Web Browser
		Provides a Web browser control (based on IE 3.0) that can display HTML pages, ActiveX
			controls, and ActiveX documents. It can be embedded within HTML documents to provide
			a browser within a browser.
	

	

		Timer
		Provides a timer control that can be programmed to execute actions/scripts at set
			time intervals.
	

	

		Marquee
		Provides a control built into Internet Explorer that scrolls any HTML file in a horizontal
			or vertical direction. The amount and delay of scrolling are configurable.
	








The following control ships with the complete installation of Internet Explorer.







	

		ActiveMovie
		Displays streaming and non-streaming media (video, sound, and synchronized images
			with sound).
	







The following controls ship with the complete installation of Internet Explorer
as well as the ActiveX Control Pad.





	

		HTML Layout
		Supports new HTML extensions published by the World Wide Web Consortium (W3C) that
			enable objects to be positioned exactly on a Web page. It displays 2D HTML regions
			inside IE 3.0 using new extensions to HTML.
	

	

		MS Forms 2.0 Label
		Creates basic text labels.
	

	

		MS Forms 2.0 Textbox
		Provides multiline text-entry and text-display windows.
	

	

		MS Forms 2.0 Combo Box
		Enables users to choose options from a drop-down list.
	

	

		MS Forms 2.0 List Box
		Enables users to choose options from a scrollable list.
	

	

		MS Forms 2.0 CheckBox
		Enables users to check an option.
	

	

		MS Forms 2.0 Option Button
		Enables users to choose between multiple options.
	

	

		MS Forms 2.0 Toggle Button
		Provides a two-state toggle button.
	

	

		MS Forms 2.0 Command Button
		Provides a basic pushbutton control.
	

	

		MS Forms 2.0 Tabstrip
		Enables users to select multiple pages via tabs. A nice real-estate-saving control.
	

	

		MS Forms 2.0 ScrollBar
		Provides basic horizontal and vertical scrollbars.
	

	

		MS Forms 2.0 Spin Button
		Provides a button that can be "pushed" up or down.
	

	

		MS ActiveX Image
		Progressively displays images in metafile, .JPG, .GIF, .BMP,
			or wavelet formats.
	

	

		MS ActiveX Hotspot
		Adds transparent hotspots to the HTML layout control.
	







Microsofts ActiveX Control Component
Gallery




In addition to the standard controls available with Internet Explorer and the
ActiveX Control Pad, Microsoft makes several other controls available on its ActiveX
Gallery Website. Table 13.2 lists the standard set of controls available. Note that
this listing represents a minimal subset of the rapidly growing number of controls
available from Microsoft and third-party vendors. This Website also provides links
to several third-party controls available for downloading and evaluation.





Table 13.2. Standard Microsoft ActiveX Controls Available from
the ActiveX Gallery Website


(http://www.microsoft.com/activex/gallery). 





	

		Control
		Function
	

	

		Animated Button
		Displays various frame sequences of an .AVI file, depending on the button
			state. It uses the Windows Animation common control. The .AVI file must
			be RLE compressed or 8-bit compressed.
	

	

		Chart
		Enables you to draw various types of charts with different styles. Great for providing
			graphical representations of data, such as that derived from database queries.
	

	

		Gradient
		Shades a given area with a range of colors (making the transition from a specified
			color to another specified color).
	

	

		Label
		Enables you to render and display text at any specified angle or along user-defined
			curves. The control supports Click, Change, MouseDown,
			MouseOver, and MouseUp events.
	

	

		Menu
		Enables developers to place menu buttons on the page that brings up a menu with the
			standard menu look and feel. Generates events that can be used in VBScripts.
	

	

		Popup Menu
		Displays a pop-up menu in response to the PopUp method being called. Generates
			an event after a menu item is clicked.
	

	

		Popup Window
		Displays a specified HTML document in a pop-up window. Can be used to provide tool
			tips or preview links.
	

	

		Preloader
		Downloads a file from a specified URL and puts it into the cache. Invisible at runtime
			and starts downloading when enabled. When the download finishes, the control fires
			a Complete event.
	

	

		Stock Ticker
		Displays continuously changing data by downloading the specified URL at regular intervals.
			The data can be in a text or .XRT format.
	

	

		View Tracker
		Generates events whenever the control enters or leaves the viewing area. Developers
			can use this control to automatically modify properties or functionality on the page
			based on sectional input.
	







	


	


RESOURCE:The Microsoft ActiveX Component Gallery
	at







	
http://www.microsoft.com/activex/gallery











	
has numerous links to Microsoft and third-party controls available for downloading
	and evaluation. Additionally, the site at

	
http://www.browserwatch.com











	
provides several links to controls developed by software vendors and other independent
	control developers. 










Registering a Control




When ActiveX controls (OCX files) are installed on your system, they are registered
with the operating system database known as the Registry. All ActiveX controls are
referenced in Web pages by their unique class identifier (CLSID). Registering
an OCX is a matter of placing this CLSID into the Registry. When you load
the OCX file into an ActiveX Chart object, for example, the following CLSID
is written into your system's Registry:


FC25B780-75BE-11CF-8B01-444553540000



This CLSID is called whenever a Web page needs to instantiate an instance
of this Chart control.



Adding Controls to HTML Documents




Let me preface this section by stating that I don't really advocate adding controls
to your HTML pages by hand. It is simply too easy to mistype something--especially
CLSID strings. Additionally, a variety of tools exist that support easy
insertion of controls into your documents; these tools include the Microsoft ActiveX
Control Pad, Microsoft FrontPage, and SoftQuad's HotMeTaL product. I highly recommend
that you at least download and learn how to use the ActiveX Control Pad (available
at the Microsoft site http://www.microsoft.com/workshop/ author/cpad/).
The ActiveX Control Pad not only enables you to easily insert controls, but it also
provides a text editor for editing HTML; an object editor for easily inserting controls
(and their hideously long CLSIDs); a page editor to create HTML layouts
(you'll see more information on these layouts in later chapters); and a script wizard
that provides easy access to a control's methods, properties, and events.


With those capabilities in mind, you still should understand how an ActiveX control
is represented in your HTML. ActiveX controls are placed in HTML by using the <OBJECT>
tag, which also includes the control's CLSID and other information (such
as height and width) as tag attributes. You can set various property values for the
control by including <param> tags within the <OBJECT>,
</OBJECT> tag pair. ActiveX controls also have sets of properties
and methods that can be set and reacted to by using VBScript. Listing 13.1 shows
how you can place an ActiveX Label control on your page. The VBScript code
shows how the Label's Click event is handled and used to display
a simple dialog box.


Listing 13.1. Placing an
ActiveX Label Control on Your Page.


<OBJECT ID="lblCat"
  CLASSID="CLSID:978C9E23-D4B0-11CE-BF2D-00AA003F40D0"
  STYLE="TOP:104pt;LEFT:6pt;WIDTH:71pt;HEIGHT:17pt;ZINDEX:6;">
        <PARAM NAME="ForeColor" VALUE="16711680">
        <PARAM NAME="BackColor" VALUE="16777215">
        <PARAM NAME="Caption" VALUE="Categories:">
        <PARAM NAME="Size" VALUE="2505;600">
        <PARAM NAME="FontName" VALUE="Arial">
        <PARAM NAME="FontEffects" VALUE="1073741825">
        <PARAM NAME="FontHeight" VALUE="240">
        <PARAM NAME="FontCharSet" VALUE="0">
        <PARAM NAME="FontPitchAndFamily" VALUE="2">
        <PARAM NAME="FontWeight" VALUE="700">
</OBJECT>

Sub lblCat_Click()
   MsgBox "You clicked my label!"
End Sub



As you can see from this example, it is worth your while to learn how to use the
ActiveX Control Pad or some other tool instead of typing all this for every control
you decide to use.



Installing and Displaying Controls




In the scheme of things, not too many of the existing ActiveX controls are included
with Internet Explorer or the ActiveX Control Pad. Instead, most controls are third-party
controls or controls that you've developed. The upshot of this is that the controls
don't initially exist on your users' machines, and in some way must exist for your
users to get the controls and register them in their system's Registry.


Fortunately, ActiveX controls are designed so that if they don't already exist
on the user's machine, they can be obtained from the source. This capability is supported
by adding the CODEBASE attribute to the <OBJECT> tag when
the control is added to your HTML. This attribute specifies the URL at which the
control is located. When Internet Explorer encounters CODEBASE in an HTML
page, for example, it checks the system Registry to see whether the control already
is registered. If it isn't, the URL is used to download and register this control
(subject to security settings on the user's system). After this one-time download,
the control is maintained locally in an object cache on the user's machine.


The following code snippet illustrates how the CODEBASE tag is used to
obtain a specific version of a control from Microsoft:


<OBJECT ID=iexr2 TYPE="application/x-oleobject"
CLSID="clsid:0CA4A620-8E3D-11CF-A3A9-00A0C9034920"
CODEBASE="http://activex.micorosoft.com/controls/iexplorer/
Âiestock.ocx#Version=4,70,0,1161">





Summary




This chapter gave you an overview of ActiveX and a glimpse at how this set of
technologies gives you the opportunity to rapidly and easily improve the quality,
interactiveness, and functionality of your Web applications. You now should understand
the important role that ActiveX technologies will play in the future of Web applications
development.


The chapter began with a brief overview of what ActiveX is and how it evolved
from earlier Microsoft technologies, such as OLE and custom controls. You then looked
at the Component Object Model (COM) and gained some insight into how ActiveX components
actually are built on this client/server object model. Next, you examined the ActiveX
Object Model. The main components of ActiveX technology were outlined: ActiveX controls,
ActiveX scripting, ActiveX documents, and the ActiveX Server framework.


The remainder of the chapter was dedicated to ActiveX controls. You were introduced
to a number of standard controls that are readily available from Microsoft. You also
learned how these controls are registered on your system, added to Web pages, and
distributed via the Web.