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Lesson -10 : ActiveX Concepts
10.8 - ActiveX Controls
ActiveX controls are tiny little Automation servers that load in process. This means they are remarkably fast. They were originally called OLE Custom Controls and were designed to replace VBX controls, 16-bit controls written for use in Visual Basic and Visual C++. (There are a number of good technical reasons why the VBX technology could not be extended to the 32-bit world.) Because OLE Custom Controls were traditionally kept in files with the extension .OCX, many people referred to an OLE Custom Control as an OCX control or just an OCX. Although the OLE has been supplanted by ActiveX, ActiveX controls produced by Visual C++ 6.0 are still kept in files with the .OCX extension. The original purpose of VBX controls was to allow programmers to provide unusual interface controls to their users. Controls that looked like gas gauges or volume knobs became easy to develop. But almost immediately, VBX programmers moved beyond simple controls to modules that involved significant amounts of calculation and processing. In the same way, many ActiveX controls are far more than just controls; they are components that can be used to build powerful applications quickly and easily. Because controls are little Automation servers, they need to be used by an Automation controller, but the terminology is too confusing if there are controls and controllers, so we say that ActiveX controls are used by container applications. Visual C++ and Visual Basic are both container applications, as are many members of the Office suite and many non-Microsoft products. In addition to properties and methods, ActiveX controls have events. To be specific, a control is said to fire an event, and it does so when there is something that the container needs to be aware of. For example, when the user clicks a portion of the control, the control deals with it, perhaps changing its appearance or making a calculation, but it may also need to pass on word of that click to the container application so that a file can be opened or some other container action can be performed. This Unit has given you a brief tour through the concepts and terminology used in ActiveX technology, and a glimpse of the power you can add to your applications by incorporating ActiveX into them. TheUnit lead you through the creation of ActiveX applications, using MFC and the wizards in Visual C++.

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