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What Is an ActiveX Control?


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Evolution of ActiveX Controls


Chapter 15

What Is an ActiveX Control?

ActiveX controls have evolved from object linking and embedding technologies. They allow user access and interaction with shared documents over the Internet or an enterprise's intranet. ActiveX, in general, consists of a number of processes that allow many, varied technologies to operate over a distributed environment such as the Internet (see Figure 15.1).

With object linking and embedding a spreadsheet from an application such as Excel and a database from an application such as Access can be made a part of the content of a document in Word. Without object linking and embedding, those object would be kept separate and you would need to run all three applications to access the data.

Figure 15.1. ActiveX is a method for implementing various technologies over the Internet.

Before you can learn how to program with ActiveX controls, there is a some background information with which you should be familiar. In today's lesson, you will learn

  • How ActiveX controls came to be

  • How ActiveX controls are used

  • Where to find ActiveX controls

  • The system requirements for using ActiveX controls


Evolution of ActiveX Controls

ActiveX controls come from half a century of software development, beginning with the early research at companies such as Xerox/PARC and Bell Labs. ActiveX controls are a marriage of an innovative method of allowing applications to interact with each other (OLE) and Microsoft’s response to the demand for a simple way to implement that interaction.

OLE

OLE (Object Linking and Embedding) is what set the advanced programmer apart from the merely experienced. To understand just what it means (no, it's not what the crowd says at a bullfight!), let's dissect the phrase:

      Object—Every "thing" on a computer system is called an object. This includes everything such as the console, applications, libraries (like many of the .DLL files in your \Windows\System directory), and so on.

      Linking —Sometimes a link is created between two separate objects on a system that allows them to share each other's information and resources. For instance, if you have a mailing list and a form letter, you will create a link between the two so that the form letter can go out to everyone on the list. If the list is modified in some way, the changes will be reflected in the mailings.

      In Figure 15.2 you see a document from a doctor in a remote location ordering new Yeti Restraints from his medical supplies company. Because he wants to include a graph in his document, and because he is using the WordPad utility that has no graphing support, he can create a link to a previously created Excel chart. This is done through the menu option Insert | Object and then by selecting the Create from File option.

Figure 15.2. The WordPad dialog box for creating a link to external data or embedding a new object within a document.

      Embedding —When you create a document in one application, sometimes you will find that the application does not allow you to work with or edit a particular kind of document.

      Referring again to Figure 15.2, if Dr. Kirbymeister had not previously created an external graph, the doctor would choose the menu option Insert | Object—but this time, he would select the Create New option instead of Create from File. Then he could create and edit the chart from within WordPad much the same as if he were using the Excel program itself.


The History of OLE

OOP (Object Oriented Programming) was developed around the middle of the century. At that time, most of its use was limited to the military, research labs, universities, and large corporations.

OLE , as a generally accepted technology, was not introduced to the public until Apple Corporation developed and marketed the later versions of the Macintosh. The Mac used the first widely accepted GUI (Graphical User Interface), and its natural programming environment was object oriented.

It was a few more years before it found global acceptance, when Microsoft incorporated OLE and OOP into millions of NT Servers and Windows 95 Workstations. Now OLE is the state of the art in Programming—almost 50 years after it was first introduced.

Uses of OLE

OLE is the technology that allows applications on a computer to interact with each other. An example of OLE is when you view an Excel spreadsheet or a Word document in a PowerPoint presentation or an Office Binder. (See Figure 15.3.)

The Office binder is utility that comes with MS Office for Windows 95. It allows a user to place several, documents in one shell. This shell then provides a method for linking the various object so that they can all reference a common set of data. This is one of the first implementations of DCOM-type technologies into a Windows95 product, since the different documents can reside on remote servers.

Figure 15.3. OLE between Office95 applications.

Using OLE technology also simplifies programmers' coding tasks. By referencing the procedures in external applications, a programmer need not go through the development steps of re-creating something his users already have. Programmers make use of this application-to-application interface to create front ends for, and retrieve data from, other programs on the same computer.

You can see another instance of OLE by following these steps:

  1. Start a new Word document.

  2. From the pull-down menu, select Insert and then Object.

  3. You should see a list of many different objects you can insert into the otherwise all-text document.

  4. From the list, select Bitmap Image.

  5. You should see that your menus and button bars have switched from the standard MS Word features to tools from Microsoft Paint (or whatever OLE Bitmap Editor your system uses).

  6. By clicking outside of the image area, you can return to the standard Word setup.


OLE Components

The application whose features one wants to access would need to support a certain set of functions. The presence or absence of these features is what makes an application OLE-enabled or not. The host application is an OLE Server and the system accessing it is the OLE client. Although the OLE Server is usually a full-blown application, it could be as simple as DLL or two. As long as it supports the interconnectivity features of OLE, other OLE-Enabled applications can use it.

The widest uses of OLE are based on COM (Component Object Model). COM defines a basic structure and set of rules for developing object-oriented programs. When a Windows OOP programmer develops their application, it is the structure of the COM model upon which their program acts.


Note
I only gave a brief discussion of COM here. After you are more familiar with ActiveX and OLE programing you may wish to reference the entire specification for the Component Object Model, as well as information about its ongoing development, at Microsoft's OLE Developer's Site at the URL http://www.microsoft.com/oledev


When creating an ActiveX control there are two features that it must implement. These are the "IUnknown" interface, and that it be self registering. The controls are then instantiated and uninstantiated through the AddRef() and Release() methods in whatever programming language you use.

OLE also proved of great benefit to software manufacturers who wanted to increase the value of their product by allowing other applications to access the features of their software. A manufacturer would publish an API (Application Programmers Interface) for its product, and developers would reference that document to see how to make their programs interact with that product. Using this complex API, the programmers would develop their own front ends for others' software, tailoring it to the specific needs of their customers.


Sharing or Stealing?
The shared nature of OOP makes it very easy for a programmer to breach the barrier between using and taking credit for another programmer's work.
When an OLE programmer creates an interface to another programmer's software, the features add value to that application. If, however, the new application is nothing more than a front end to another application, credit should be given to the original programmer.


The only real drawback to this is that the API can be very difficult to understand for a programmer who is not familiar with the program. Although OLE coding is complex, it is still not as complex as it would be without the standardization of OLE features.

VBX—16-bit Custom Control

The VBX was the first "custom control." It incorporated the features of an API into a single item that could be added to a program. This item would enable the programmer to access the features of a given item without needing to know the more complex features of OLE. Each control enabled users to interact with a specific OLE component or set of components.

Visual programming systems (like Visual Basic and Access), which are OLE container applications, could now access complex features of an external object with just a few lines of code. Although the processes the VBX uses are not true OLE, in the strictest sense, this "mock OLE" is still quite powerful.

The development of custom controls brought an additional benefit to programmers, many of whom were working with programming languages that were not true OOP. Although the VBX was not a true OLE component, it broke ground in enabling programmers to access functionality within external software components.

OCX—16/32-bit Object Controls

OCX controls were developed in response to the need for simpler, yet more powerful, access to control and OLE functionality. Lower-level VBXs just did not do it. Although most of these controls are still not, by definition, true OLE controls, many of them incorporate the more complex (and frequently needed) OLE functions. The enhanced "mock OLE" of the first OCX’s filled most of this demand.

Custom controls like VBXs and OCXs provided an excellent way of incorporating complex features into a simple package. As with any technology that proves valuable, programmers began demanding more from these tools—demanding that developers incorporate actual OLE features into them. Indeed, OCXs met this demand so well that there is still some confusion and debate among programmers about whether OCXs are true OLE controls. They were not yet, however, true OLE controls.

ActiveX Controls


ActiveX controls were introduced to combine two distinct areas in the evolution of computer technologies: custom controls and a rethinking of the basic ideas behind OLE and OOP.

These new controls are the first DCOM (Distributed Component Object Model)-based OLE controls. As I've mentioned, prior OLE interfaces were based on COM. Therefore, ActiveX is the first true OLE control.

In DCOM, the programmer no longer programs for an individual computer, but rather for the environment, or network, within which computers operate. In the older COM model, a programmer need only follow a set of rules on how the computer and the user would interact. With DCOM, the programmer is provided with a set of rules by which computers, in general, interact with each other over the Internet or an intranet.

How ActiveX Controls Are Used

Two similar methods are used to interact with ActiveX controls—programmatic and through script. When using VBScript, the line between the two is blurred because it so closely follows the structure of the Visual Basic programming language.

Programmatic


One of the neatest things about ActiveX controls is the way they blur the line between Internet controls and regular programming controls such as command buttons and drop-down list boxes. ActiveX controls can be used within hypertext documents as well as within full-blown programs. The major difference between the two uses is that scripting uses a degree of restricted functionality for many controls when used in a network document. When these same controls are used in an OLE container application (such as Visual Basic or Visual C++), they can be programmed with all the power of the programming language used.

Using ActiveX with Visual Basic/VBA

Although the programming of ActiveX controls is possible today through Visual Basic 4.0, the integration of ActiveX into a programming language is mature only in versions of Visual BASIC after version 4. Visual Basic and VBA (Visual Basic for Applications) will be the first programming languages to incorporate ActiveX into their environments.

Programmers who make use of Visual Basic to program with ActiveX will find it simple to port their applications to the Web by replacing their VB code with VBScript. Most of the syntax and other conventions will remain the same, and most of the code will need very minor revisions to work the same as it did in the compiled version. In fact, VBScript is actually just a subset of VBA.

This code will send 100 alerts to the user in Visual Basic:

Sub cmdWarnUser
For x = 1 to 100
msgbox "Alert!"
Next X
End Sub

This code will do the same thing in VBScript:

Sub cmdWarnUser
For x = 1 to 100
alert "Alert!"
Nest x
End Sub

Using ActiveX in Other Languages

Visual Basic and VBA are the programming environments in which most of the ActiveX controls are designed to be used. They can be used, however, in any programming environment that supports DCOM-based OLE. These programming environments are called OLE Container applications. A few of these are Visual Basic, Access, Visual FoxPro, Turbo C++, and Visual C++.

ActiveX Scripting

ActiveX scripting adds a level of control to Internet documents and allows the programmer to automate and activate Web pages. It does this through the use of server-side and client-side scripts (which was covered earlier in this guide). The HTML page itself can have bits of script (client-side) such as VBScript and JScript, which provide a level of automation for use on the client machine. The server then can have its own scripts, such as ISAPI and CGI, which provide a level of automation for use on the server machine.

Server Scripts

Without client scripting, the only way to program a Web document is through a server script such as ActiveX ISAPI, HTTP CGI, or UNIX Perl. These scripts are very powerful, but they require a Web page manager to have access to a server's executable files.


Loading CGI Scripts on an ISP's Server
Unless you operate your own HTTP server locally, it can be very time-consuming to upload, test, and configure your own server scripts.
First you must select the language in which you are going to write your script. Most (if not all) ISPs (Internet service providers) use UNIX as their server operating system—and most users do not. Perl scripts usually work best on those systems. Some systems also support CGI scripting, but those scripts must be written in C++. Some HTTP servers support CGIs that are written in VB as well. MS Internet Information Servers support the new ActiveX Server Scripting, called ISAPI. The language you choose depends on the HTTP server software. Should your ISP change its system, you may need to rewrite and re-compile your server scripts.
After you have written your script(s), you must put them into your HTTP server's script directory (usually something like \CGI-BIN\). You will need special permission from your ISP to access this directory because its other users will be using the same directory. Consideration should be paid to those other users by not bothering the other scripts in the directory.
Most scripts will need to be uploaded to the server (and made public to the world) just to enable testing on them. Testing a server script on a local machine would result in some unexpected results.
All this makes the capability to script within HTML documents (that is, client-side scripting) easier on the Web page author and safer for the ISP and its users.


For many ISPs, this level of user access to their servers is unacceptable and they disallow it (or charge a premium for it). Server scripting gives the scriptwriter access to a large portion of the ISP's server configuration. The malicious or uninformed writer could cause problems—not only on the ISP's servers, but to its customers' machines as well.

HTML Script

The IETF (Internet Engineering Task Force) has established a standardized method for coding script within an HTML (hypertext markup language) document. This standard defines how all scripts are supposed to work within a Web Document.


URL
This site contains the full text of all the current Internet Standards (RFCs) in their final forms. You can also reference proposed specifications through this site:

IETF http://www.ietf.org



JavaScript

JavaScript is the first widely used language based on the HTML scripting standard. It was developed by Sun Microsystems to support Java applets. The similar naming of the scripts and the objects often causes confusion when talking about either in conversation—but they are two completely different beasts.


Note
Sun Microsystems provides information on the Java specification (which it developed) on its Web site at JavaSoft http://www.javasoft.com.


ActiveX honors the JavaScript standard and allows interaction between JavaScript, VBScript, Java Controls, and ActiveX Controls.

VBScript

VBScript , which you learned about earlier, is Microsoft's answer to JavaScript. It also allows a programmer to place his code and objects in an HTML document. Because VBScript is part of the ActiveX line of technologies, it supports programmatic control of both Java applets and ActiveX controls. Anyone with an MSIE (Microsoft Internet Explorer) Web browser can run VBScript.


Note
Microsoft's VBScript site contains information on the VBScript language. You can find it at http://www.microsoft.com/vbscript.



Security

Parents, guardians, employers, and others provide those in their charge with Internet access in order to increase their productivity and overall value. However, with this added power comes a need to be protected from inappropriate, dangerous, or downright malicious activity. ActiveX provides a framework over which a very effective security system can be laid.

Threats

Because scripting is such a powerful tool, it is of great value in distributing information according to a multitude of client system requests. This punches a wide hole in most enterprises' security.

Security can be breached by allowing foreign programs access to internal information systems. Dangerous or malicious activity by scripts can be brought on through programmatic events such as file I/O. The threat is not less for an individual system than it is for a larger network.

Protection

In order to protect yourself from malicious programs, there are a couple of security policies you will want to implement on your system. These should protect you against

  • Users who wish to gain unauthorized access to your system

  • Malicious code, in the form of viri.

  • Bad behavior on the part of downloaded ActiveX Components.


Standard

Because most security boils down to three basic levels (UserID, Password and/or physical location), the wise administrator will keep the most sensitive information unavailable to the Net. Each user and system administrator should determine the level of protection (and the resultant impact upon interoperability) within which their particular system should operate.

AntiVirus

Any system that has a disk drive or network connection or other way of accessing files (and being accessed for files) is exposed to threats from viral infection. An AntiVirus program should be running on any system with such interconnectivity. Microsoft AntiVirus, Norton AV, McAfee AntiVirus, and many other utilities provide a basic level of security that should catch most threats from viral infection.


Note
McAfee has dominated the anti-virus market throughout the last decade. Learn where to get the latest copies of their anti-virus software at http://www.mcafee.com.



ActiveX

In response to the threat that scripting exposes, a wide variety of methods have been developed with and without the ActiveX technologies to protect systems against threats such as malignant code and corrupt controls. Some of these methods include Internet ratings, code signing, trust verification, and user locator services .

Where to Find ActiveX Controls

ActiveX controls are available from many sources. Controls that software manufacturers, corporate marketers, and even hobbyists post on their Web pages can automagically find their way to systems all over the world. The nature of ActiveX controls makes it almost too simple for users to load them onto, and install them into, their machines.

World Wide Web


The easiest way to obtain new software of any kind, especially ActiveX controls, is by way of the World Wide Web (a.k.a. "WWW" or "The Web"). As ActiveX is being implemented all over the world, the Web is turning out to be the most effective distribution channel as well as a way to communicate. (Why order something through the mail, with all of its overhead, cost, and inefficiencies, when it can be downloaded as needed and with immediacy?)

Automatic Installation from Web Pages

When a user points his browser to a standard Web page (or HTML document), the page of text is displayed in the browser window. This is the quickest, cheapest, easiest way to acquire a new ActiveX control. When a user views a page containing ActiveX controls, and using an ActiveX-enabled browser, activities to load and use those controls are launched. Part of this process is to prompt the users for whether they want to load and install the controls (and, of course, expose themselves to the threat those controls may pose).


Note
If the control does not require a user license, you can immediately start programming with it. In fact, you can program with it immediately anyway. You just cannot distribute your application until you have a license to do so.


During the installation, the control is loaded onto the user's system. If the Web page creator referenced an .INF file, that file will tell the user's system what files to get, where to get them, and how to add them to the system registry as necessary.

At this point, a number of different security activities are performed to assure the integrity of the control.

Software Distributors

At the time of this writing, Microsoft has ActiveX in the beta test phase of its development. Still, many software developers have already released their ActiveX applications. It's probably safe to say that ActiveX (or DCOM), however it matures or who takes it the farthest, is a standard that will be developed upon heavily—even if Microsoft never releases it in a final form!

ActiveX Web Browsers

There are a wide variety of Web browsers on the market—each capable of viewing hypertext documents.

In the earliest days of the Web, text-only browsers such as Lynx were the standard. These browsers allow users to read the content of a Web page over a slow (less than 9600 baud) connection. Any graphic content (which can swell the size of a document significantly) is not retrieved unless the user specifically asks for it.

In the early 1990’s, the National Center for Supercomputing at the University of Illinois at Urbana-Champaign developed a graphical Web browser called Mosaic that proved very popular on the net. Soon afterward, Netscape jumped on the WWW bandwagon, developing and releasing its Navigator Web browser. By this time, use of the Web by previous nonusers was increasing by leaps and bounds, and a wide variety of (sometimes incompatible) Internet utilities was being released to the general market.

To maintain dominance in the computing industry, Microsoft followed suit in a big way with the development of ActiveX browsers that not only allow text and graphics, but a plethora of other types of content, such as music, video, and a special Internet flavor of SQL (Structured Query Language).

Internet Explorer

Beginning with version 5.0 of MSIE, Microsoft has chosen its free Web browser as the developmental and presentation platform for the introduction of ActiveX technologies. Needing no plug-ins or additional software, it is the most effective tool for applying the features of activated HTML pages.


The term "ActiveX" comes from Bill Gates’ directive to his staff to "Activate the Internet". Internet programmers will often refer to a standard web feature, such as text browsing and file transfer, as "activated", if it has the OLE or other advanced features of ActiveX.


Note
The Internet Explorer home page is found at http://www.microsoft.com/ie. Information on MSIE and its related technologies can be found here and is updated regularly.
The Netscape home page is found at http://www.netscape.com. Information on Netscape Navigator and its plug-ins and accessories can be found here, and is updated regularly:



Netscape Navigator

There is a wide variety of Web browsers used to access the World Wide Web, and Netscape Communicastor is currently the Web browser of choice for most users. In spite of this wide use, however, it does not internally support ActiveX.


Installing Netscape and MSIE on the Same Machine
As a developer, you will need to be able to see how others will view your pages. As long as competition is alive and well, users will access your pages with a variety of different browsers. Netscape and MSIE are the two most popular (for now).
On a Windows98 machine, you can enable the use of both browsers by following these instructions:

  1. Obtain the most recent copy of MSIE from its Web site. (The CD-ROM that came with this guide has a copy of the version that was current at the time of printing.)
  2. Obtain the most recent copy of Netscape Navigator from its Web site.
  3. Run the installation process for MSIE. When it is done, reboot your machine.
  4. Run MSIE by double-clicking on the Internet icon on your desktop. (You can take this opportunity to customize the settings from the View | Options menu.) Exit the program and continue to the next step.
  5. Run the installation process for Netscape Navigator. When it is done, reboot your machine.
  6. Run Netscape by double-clicking the Netscape Navigator icon on your desktop. (You can take this opportunity to customize the settings from the Options menu.)
  7. At this point, Netscape will ask you if you want to use it as your default browser. If you will be doing your development work in ActiveX, you should select No and check the box that says Do not ask this question again". Exit the program and continue to the next step.
  8. Run MSIE one more time by double-clicking on the desktop icon.
  9. At this point, Windows will ask you if you want to use MSIE as your default browser. If you will be doing your development work in ActiveX, you should select Yes and check the box that says Do not ask this question again. Leave MSIE running and continue to the next step.
  10. Select the View | Options menu item. Then select the File Types tab, select the Internet Document (HTML) item, and press the Edit button. This should bring up a window with a section titled Actions.
  11. Press the New button.
  12. For Action, enter View with Netscape
  13. For Application", enter netscape.exe


Now, when you right-click an Internet document, you will have the option of viewing it with Netscape or opening it with MSIE .



NCompass Labs

NCompass Labs makes a plug-in for Netscape that adds some ActiveX functionality to it. Because Netscape does not yet have ActiveX functionality, a plug-in such as this is necessary to browse ActiveX documents with that browser.


Note
Find the NCompass Labs home page at http://www.ncompasslabs.com. You can find the company's ActiveX plug-in as well as its other products here.



ActiveX Controls

Microsoft has released a number of ActiveX controls into the public domain. Any developer may use most of these tools, royalty free, to develop and distribute his applications. Some of these include the HTML Layout Control, the Active Marquee Control, and (possibly the most important of all) the ICP (Internet Control Pack).

The ICP is a set of ActiveX controls , incorporating the standard Internet protocols. These controls include

FTP Control File Transfer Protocol
NNTP Control Network News Transfer Protocol
POP3 Control Post Office Protocol
SMTP Control Simple Mail Transfer Protocol
HTTP Control Hypertext Transfer Protocol
HTML Control Hypertext Markup Language
WinSock Control Windows Sockets API

Microsoft licensed the controls in the ICP from NetManage, who has also has placed them in the public domain. You will learn more about the ICP later .

ActiveX System Requirements

The DCOM model behind ActiveX is designed to be usable across a variety of systems. Cross-platform compatibility has always been the holy grail of systems development. The variety of systems and the exponentially higher number of possible configurations and software packages installed on those systems makes this task all but impossible.

Operating Systems

ActiveX controls are usable on any system that supports DCOM. The first to incorporate this technology is Windows 95, with Windows NT version 4.0 following close behind. Microsoft is working with software vendors to enable ActiveX on UNIX and Macintosh in the near future.

Required Files

In the following lessons, you will be introduced to some specific ActiveX controls; any files required to run them will be noted. A few are basic to the use of ActiveX.

For a Windows 95 installation, the files that may need to be made available to the user are discussed in the sidebar titled "ActiveX File Dependencies." If you use any other controls, you may want to keep a similar chart as a reference for what other files those controls may require.

There is no one file or one group of files that you can use to make your system a complete ActiveX or DCOM system. Each feature has its own requirements. Windows NT 4.0 is based on DCOM, and others will certainly follow, but other operating systems must use an add-in (such as the Internet Explorer version 3.x for Windows 95) to use ActiveX features.


ActiveX File Dependencies
Microsoft Foundation Class–based custom controls (OCXs)require MFC40.dll, MSVCRT.dll, and OLEPro32.dll.
Trust Verification services require WinTrust.dll and digsig.dll.



ICP Controls
All of the controls in the Internet Control Pack require the NMSCKN.dll in addition to their .OCX control, and all but the WinSck.ocx requires NMORENU.dll and NMOCOD.dll.
The FTPct.ocx requires the additional NMFTPSN.dll. The HTML.ocx requires the additional NMW3VWN.dll.
Many ActiveX packages may also require the installation of DirectX to operate. DirectX was originally developed as Microsoft's Game SDK (Software Developer's Kit). DirectX gives the programmer a powerful tool for accessing the more complex features of 3-D video and sound.



Other ActiveX Controls
Included with the ActiveX SDK are two redistributable, packaged, self-installing files that will install the controls most important for ActiveX on Windows 32-bit machines.
WintDist.exe (WinINet) installs the most basic Windows Internet files—WinInet.dll and InLoader.dll.
AXDist.exe (ActiveX) will install the WinINet files and the additional ActiveX controls—WinINet.dll, InLoader.dll, URLMon.dll, HLink.dll, HLinkPrx.dll, OLEAut32.dll, and STDOLE2.tlb.



Summary

In this chapter, you have been introduced to ActiveX controls and the concept of COM (Component Object Modeling) and the emerging DCOM (Distributed Component Object Model).

ActiveX controls are the first wide implementation of DCOM, and provide the programmer with a simplified interface to the highly complex features of OLE in an internetworked environment. These controls are the product of the evolution of custom controls and OLE and the market demand for a system that combines the two.

ActiveX controls can be embedded within an HTML document or in an application developed in an OLE Container IDE (Integrated Development Environment) such as Visual Basic. The programmer can then develop a user interface to those controls using VBScript or another scripting language. The programmer can also use those same ActiveX controls, programmatically, to develop standalone client or server applications.

ActiveX controls can be acquired quite easily, and almost by accident. An individual who is browsing the Web and accesses a page with ActiveX controls embedded within it may receive a prompt asking if he wants to install the custom control. Also, when a user installs an application that uses ActiveX controls, those controls are installed on and made available to their system.

Although the ActiveX controls themselves will not necessarily work on every machine, a user's Windows 95 system can be easily upgraded and modified to support them. This is done by installing a few freely redistributable files on the user's system.

Q&A

  • Q How complicated are OLE and the COM model?

  • A Very! One could go as far as to say it is the most complex to understand, yet the most basic to use, concept in object-oriented programming. This is because it is the basis of OOP. Most of your ActiveX programming will be in a scripting language like VBScript or JavaScript, or in an interpreted programming environment like Visual Basic or Access. The most important features of OLE are exposed to these programming systems through the properties, methods, and events of ActiveX controls. To access the lower-level features of OLE, a program must support the interaction with MFC (Microsoft Foundation Classes). If you do not use MFC, you will have to make sure your code implement the many classes required of an OLE server. For this you would need a much lower level of language, such as Visual C++.

  • Q Is a Java applet the same as an ActiveX control?

  • A No. Java applets could best be defined as Internet-aware custom controls. Because these applets are not OLE enabled, they are not true ActiveX controls. From a scripting or interpreted language standpoint, however, working with Java applets is very similar to working with ActiveX controls. ActiveX will support the Java Virtual Machine.

  • Q Is it possible to receive a control that will perform maliciously on my machine?

  • A Yes—if you are not careful. Different Web browsers have varying degrees of security that the user can enable or disable as he sees fit. There are a number of methods an ActiveX control developer can use to assure the users of his product that they are receiving a genuine product. It remains up to the user, for the most part, to let those features work and not disable them.

Workshop

Retrieve copies of, or create shortcuts to, the following ActiveX-related specifications (Note: The URLs mentioned only show the specification's sponsor's home page.):

Quiz

  1. Explain the significance of each of the following:

    1. OLE

    2. VBX

    3. OCX

 

  1. When was object-oriented programming developed?

  2. What are the two methods for interacting with ActiveX controls?

  3. What is the name of the new technology behind ActiveX controls?

  4. If you develop an HTML document with embedded ActiveX controls, what scripting language, besides VBScript, can you use to program the user interface to those controls?

  5. If you develop an ActiveX application for a Web document, what would be the easiest programming language to use to make it a standalone application?

  6. What is the most common file that must be installed on a user's machine to enable Windows Internet functionality?

  7. What do COM and DCOM mean?

  8. Name one operating system that has built-in support for DCOM.

  9. Within what two types of items can an ActiveX object be incorporated?

  10. What copany developed the JAVA tecnhologies?

  11. An ActiveX control must support what two features?

  12. What basic concept is behind the shift from COM to DCOM?

  13. What operating systems are able to implement DCOM?

  14. What operating systems are able to run ActiveX?

  15. What features are used in the most basic level of security?

  16. What filetype tells an ActiveX browser how to register a control?

  17. What must a user obtain, after he installs the control, in order to redistribute his applications?

  18. What is the difference between JavaScript and a Java applet.

  19. Of what programming language is VBScript a subset?



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