Skip to main content

What Is an ActiveX Control?

ActiveX controls are components that can be used to add new functionality to your application.

ActiveX technologies are all built on top of the COM specification. In COM, an interface is a group of related functions that are implemented together. All interfaces are named beginning with I, such as IDataObject.

An ActiveX control must be a COM object. This means that an ActiveX control must support IUnknown, the interface supported by all COM objects. This allows for a great deal of latitude when deciding how a control is to be implemented;

Support for the IUnknown interface is provided automatically when you use MFC and ControlWizard to build your control.

Reducing the number of required interfaces allows ActiveX controls to be much smaller than the older OLE controls. It also makes it feasible to use ActiveX controls to implement functionality where the size of the control is an important factor. Web pages can be more intelligent when a control is downloaded and activated to your browser. For example, Microsoft's Internet Explorer has support for downloading ActiveX controls from a Web page. Although this opens a lot of exciting functionality, the size of the control to be downloaded must be kept as small as possible.

Interaction with an ActiveX component can be done properties, events, and methods.

  • A property is an attribute associated with the control.

  • An event is a notification message passed to the container by the control.

  • A method is an exposed function that can be applied to the control via IDispatch.

Properties

Properties are exposed by ActiveX controls, as well as by the client where the control is located. There are four basic types of properties:

  • Ambient properties are provided to the control by the container. The control uses these properties in order to "fit in" properly. Commonly used ambient properties include the container's background color, default font, and foreground color.

  • Extended properties are implemented by the container but appear to be generated by the control. For example, the tab order of various controls in a container is an extended property.

  • Stock properties are control properties implemented by the ActiveX control development kit. Examples of stock properties are the control font, the caption text, and the foreground and background colors.

  • Custom properties are control properties that you implement.

Events

An event is used to send a notification message to the control's container. Typically, events are used to notify the container when mouse clicks or other events take place. There are two basic types of events:

  • Stock events are implemented by the ActiveX control development kit and are invoked just like a function call, such as FireError.

  • Custom events are implemented by you, although the MFC class library and ClassWizard handle much of the work for you.

Methods

OLE Automation, now just Automation, is a way of enabling a COM object to be controlled by another party. Automation is provided through the IDispatch interface.

Automation was originally developed so that interpreted languages such as Visual Basic could control COM objects. Now most ActiveX controls use Automation to allow all sorts of programs--even those built using scripting languages such as JScript and VBScript--access to the methods of ActiveX controls.

Labels:

Comments

Post a Comment

Popular posts from this blog

Explain Polymorphism and Flavors of Polymorphism...

Polymorphism is the ability of different objects to react in an individual manner to the same message. This notion was imported from natural languages. For example, the verb "to close" means different things when applied to different objects. Closing a door, closing a bank account, or closing a program's window are all different actions; their exact meaning is determined by the object on which the action is performed. Most object-oriented languages implement polymorphism only in the form of virtual functions. But C++ has two more mechanisms of static (meaning: compile-time) polymorphism: Operator overloading. Applying the += operator to integers or string objects, for example, is interpreted by each of these objects in an individual manner. Obviously, the underlying implementation of += differs in every type. Yet, intuitively, we can predict what results are. Templates. A vector of integers, for example, reacts differently from a vector of string objects when it receives ...
17 comments
Read more

Function name mangling for C++ and Java

G++ internals - Mangling Both C++ and Jave provide overloaded function and methods, which are methods with the same types but different parameter lists. Selecting the correct version is done at compile time. Though the overloaded functions have the same name in the source code, they need to be translated into different assembler-level names, since typical assemblers and linkers cannot handle overloading. This process of encoding the parameter types with the method name into a unique name is called name mangling . The inverse process is called demangling . It is convenient that C++ and Java use compatible mangling schemes, since the makes life easier for tools such as gdb, and it eases integration between C++ and Java. Note there is also a standard "Jave Native Interface" (JNI) which implements a different calling convention, and uses a different mangling scheme. The JNI is a rather abstract ABI so Java can call methods written in C or C++; we are concerned he...
5 comments
Read more