ACTIVEX

by A. Reyhan Serim

I. INTRODUCTION TO ACTIVEX

ActiveX is set of technologies that enables software components to interact with one another in a networked environment, regardless of the language in which they were created. ActiveX is built on the Component Object Model (COM).

COM provides the infrastructure used when OLE (Object Linking and Embedding) objects communicate with each other. OLE is a mechanism that allows users to create and edit documents containing items or “objects” created by multiple applications.

COM is the technical cornerstone for the ActiveX technology; it defines how objects expose themselves for use within other objects and how objects can communicate between processes and across a network. COM also defines the object's life cycle. COM objects can be easily integrated for use in many languages, such as Java, Basic, and C++. COM objects are reusable binary components.

ActiveX controls, formerly known as OLE controls, let you develop sophisticated controls based on the COM that can be installed in dialog boxes or any ActiveX control container application, including pages on the Internet’s World Wide Web and Visual Basic applications. Unlike Visual Basic (VBX) controls, ActiveX controls can be built in either 32-bit or 16-bit versions. With some work, you can convert existing VBXs to ActiveX controls.

An ActiveX control is an COM-based object that can draw itself in its own window, respond to events (such as mouse clicks), and be managed through an interface that includes properties and methods similar to those in Automation objects. The only limitation on the kinds of ActiveX controls you can create is your imagination.

These controls can be developed for many uses, such as database access, data monitoring, or graphing. Besides their portability, ActiveX controls support features previously not available to custom controls, such as compatibility with existing OLE containers and the ability to integrate their menus with the OLE container menus. In addition, an ActiveX control fully supports Automation, which allows the control to expose writable properties and a set of methods that can be called by the control user.

Beginning with MFC 4.2, you can create windowless ActiveX controls and controls that only create a window when they become active. Windowless controls speed up the display of your application and make it possible to have transparent and nonrectangular controls. With MFC versions 4.2 and later, you can also load ActiveX control properties asynchronously.

II. ActiveX Is an Open Platform for Internet/Intranet Applications

As seen in Figure 1, ActiveX consists of a client-side platform, a server-side platform, development tools, authoring tools, and networking technologies. ActiveX will provide users, Webmasters, and developers with a rich platform for innovative applications on the Internet, while preserving their investments in applications, tools, knowledge, and code.

a. ActiveX on the Client

ActiveX on the client is the client-side platform that enables applications and content to be run and viewed on an end user's system. Applications and content can be either present on the client system itself or automatically downloaded from the server and viewed and run on the client. ActiveX on the client consists of:

· Microsoft Internet Explorer, which brings the benefits of ActiveX to end users and enables them to run Java applets and ActiveX controls written in Java, Visual C++, and other languages.

· Scripting engines for running scripts written in VB Script and JavaScript.

· ActiveX controls bundled with Internet Explorer for viewing and editing different kinds of content such as ActiveVRML™ (for 3D virtual reality modeling), ActiveMovie™ (for audio/video), and more.

With ActiveX on the client, users can run ActiveX controls written in different languages, such as Java, Visual C++, Visual Basic, and others. ActiveX on the client supports HTML 3.0 content, including support for frames, stylesheets, and tables.

b. ActiveX on the Server

ActiveX on the server is the server-side platform that provides clients with Internet services, applications, data, and content. Applications and content can be hosted on the same server that runs the Web Server or on other systems. Data can be hosted in any SQL database or any database that supports Open Database Connectivity (ODBC). With ActiveX on the server, developers can write Common Gateway Interface (CGI) applications, Internet Server application programming interface (ISAPI) Dynamic Link Libraries (DLLs) that run on the server side, and scripts. ActiveX on the Server consists of:

· Microsoft Internet Information Server, which supports CGI applications, ISAPI DLLs, connectivity to databases, and so forth.

· Server side scripting, code named Denali.

· Transactions, code named Viper.

· Message Queuing, code named Falcon.

III. Why Use ActiveX

ActiveX Controls and Scripting give developers the infrastructure needed to add language- and tool-independent extensions to Web pages. ActiveX provides developers, end users, and Webmasters a wide choice of existing technologies and applications that can be used for the Internet/intranets as well as new technologies such as Java. Developers get a wide selection of tools and languages to choose from in order to develop Internet/intranet applications. For example, developers can build Internet/intranet applications using Microsoft Visual C++, Microsoft's Java development tool Visual J++, Borland C++, Symantec C++, and the next version of Microsoft Visual Basic. Webmasters can choose from several authoring tools to develop powerful content including applications, while Web producers have a choice of over 1,000 shrink-wrapped components, available today, to add interactivity to their Web sites.

ActiveX is compatible with existing investments in software, hardware, and human resources. Using ActiveX Controls lets developers take advantage of existing OLE development tools and the investment they have already made in OLE. For example, developers can leverage their existing knowledge of Microsoft Visual C++ to develop applications for the Internet and intranets using the same tool. Visual Basic developers can leverage their existing Visual Basic knowledge to develop scripts for the Internet using Visual Basic Scripting Edition (VB Script), an open scripting language for the Internet. With Visual Basic, developers can use their existing knowledge and code to develop Internet and intranet applications. Java developers can write applications in Java that expose COM interfaces and that use COM interfaces, building upon existing investments in components and knowledge. ActiveX also provides support for a wide selection of networking protocols and standards such as TCP/IP, HTTP, NNTP and SMTP.

ActiveX combines the benefits of the World Wide Web and the personal computer to enable interactive distributed applications and richer communications between users. ActiveX has also greatly improved extending the HTTP and FTP protocols. The ActiveX encapsulate a new protocol that supports the concept of binding to a URL dynamically from within your application. An application binds to a URL moniker, which then communicates through the appropriate protocol to activate the OLE object.

Microsoft ActiveX supported standards

Area	Standards and Technologies in ActiveX (partial listing)
Networking	TCP/IP, IPX/SPX, PPP, SLIP, DNS, RIP, PPTP, DHCP, WINS, IPng, SSL
Web	HTTP, HTML, VRML
Communication	RTP, T.120, T.127, H.323, RSVP
Messaging	SMTP, X.400, MIME, POP3
Databases	ODBC (ISO 9942), SQL
Programming Languages	ANSI C (ISO 9899), ANSI C++, Java, Basic
Directory	X.500
Miscellaneous	FTP, Gopher, Telnet

IV. ActiveX Components

An ActiveX component is a unit of executable code, such as an .exe, .dll, or .ocx file, that follows the ActiveX specification for providing objects. ActiveX technology allows programmers to assemble these reusable software components into applications and services.

Component software development using ActiveX technology should not be confused with object-oriented programming (OOP). OOP is a way to build object-based software components; ActiveX is a technology that allows you to combine object-based components created using many different tools. To put it another way, OOP is concerned with creating objects, while ActiveX is concerned with making objects work together.

a. ActiveX DLL

Components provide reusable code in the form of objects. An application that uses a component’s code, by creating objects and calling their properties and methods, is referred to as a client.

Components can run either in-process or out-of-process with respect to the clients that use their objects. In-process server objects are implemented in a dynamic-link library (DLL) and are run in the process space of the controller. Since they are contained in a DLL, they cannot be run as stand-alone objects. An in-process component, or ActiveX DLL, runs in another application’s process. The client may be the application itself, or another in-process component that the application is using.

b. ActiveX Exe

Out-of-process server objects, or ActiveX Exe, are implemented in an executable file and are run in a separate process space. Access to in-process objects is much faster than to out-of-process server objects because automation does not need to make remote procedure calls across the process boundary.

c. ActiveX Control

An ActiveX control, like a built-in control, is an object that you place on a form to enable or enhance a user's interaction with an application. ActiveX controls have events and can be incorporated into other controls. These controls have an .ocx file name extension.

d. ActiveX Document

ActiveX documents are forms that can appear within Internet browser windows. Visual Basic ActiveX documents offer built-in viewport scrolling, Hyperlinks, and menu negotiation.

ActiveX documents are designed the same as Visual Basic forms. They can contain insertable objects, such as Microsoft Excel pivot tables. They can also show message boxes and secondary forms.

V. Deploying an ActiveX Document in Internet Explorer

You link to ActiveX documents from an HTML page with a combination of HMTL and VBScript. In the following example, an ActiveX document is reached from a hyperlink on an HTML page.

· Use HTML to provide a link to the HTML page referencing the ActiveX document.

Since the ActiveX document will replace the HTML page in Internet Explorer, it's necessary to place the component's OBJECT tag on a separate HTML page, then jump to that page — which will promptly disappear when the ActiveX document has been loaded.

The following HTML code creates a hyperlink from the first page to the second (the one that downloads the ActiveX document):

<a href="Accounts.htm">View or update accounts</a>

· Use HTML to provide a means for the browser to download, register, and navigate to the ActiveX document.The following HTML fragment instructs Internet Explorer to download the ActiveX component and register the ActiveX document in the Windows registry:

<OBJECT

classid="clsid:2F390484-1C7D-11D0-8908-00A0C90395F4"

codebase="Accounts.cab#version=1,0,0,0">

</OBJECT>

The OBJECT tag in this example includes:

· The ActiveX document's class ID so that it can be included or found in the Windows registry.

· A CODEBASE attribute to tell the browser where to find the component if it's not already on the client machine (and a version number to check against for updating).

· On the same page, place VBScript that instructs Internet Explorer to navigate immediately to the ActiveX document through its .vbd file (this file was created when the ActiveX document was compiled, and contains a pointer to the component providing the ActiveX document's objects).

Sub Window_OnLoad

Document.Open

Document.Write "<FRAMESET>"

Document.Write "<FRAME SRC=""Accounts.vbd"">"

Document.Write "</FRAMESET>"

Document.Close

End Sub

</SCRIPT>

This code fragment contains only the name of the .vbd file is given, rather than a fully-qualified path. Using this relative path to the file, Internet Explorer will look for it in the same directory as the .htm file containing the VBScript.

ActiveX controls enliven and add power to your HTML pages. In addition to controls you create, you can use three controls provided with the Professional and Enterprise editions of Visual Basic to extend standard applications with Internet technology.

VI. ActiveX Controls On an HTML Page

Using HTML and VBScript, you can include ActiveX controls on an HTML page, set their properties, call their methods, and handle their events. Given this, an HTML page containing controls is somewhat like a Visual Basic designer.

In general, ActiveX controls help to make HTML pages more vibrant with interactive or animated user interface features.

You reference and script ActiveX control behavior with a combination of HMTL and VBScript. In the following example, two label-style controls are embedded to provide clickable table of contents entries.

· Use HTML to provide a means for the browser to download, register, and reference the ActiveX controls.

<OBJECT

classid="clsid:2F390484-1C7D-11D0-8908-00A0C90395F4"

codebase="http://www.mysite.com/controls/label.ocx#version=1,0,0,0"

id="Welcome"

width="150"

height="20"

align="center"

vspace="0"

</OBJECT>

<OBJECT

classid="clsid:2F390484-1C7D-11D0-8908-00A0C90395F4"

codebase="http://www.mysite.com/controls/label.ocx#version=1,0,0,0"

id="Catalog"

width="150"

height="20"

align="center"

vspace="0"

</OBJECT>

The OBJECT tags in this fragment include:

· The controls' class IDs so that they can be included or found in the Windows registry.

· An ID attribute to use when referencing the controls in VBScript (similar to the Name property in Visual Basic).

· A CODEBASE attribute to tell the browser where to find the component if it's not already on the client machine (and a version number to check against for updating).

· PARAM NAME tags to set the controls' property values.

· Use VBScript to call handle click events so that clicking each control will load a specific .htm file in a specific HTML frame:

Sub Welcome_Click

Parent.Parent.Frames(1).Location.Href="Welcome.htm"

Welcome.ForeColor = 000000

End Sub

Sub Catalog_Click

Parent.Parent.Frames(1).Location.Href="Catalog.htm"

Catalog.ForeColor = 000000

End Sub

</SCRIPT>