Adding a Custom Notification Property

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Circle: ActiveX Control, Lesson 3

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The ability to define a custom set of properties, events, and methods for a control is one of the most powerful features of control writing. The previous lesson illustrated the use of a stock property. This lesson illustrates how to add a custom property to the Circle control.

Note   You can find a finished example of this lesson's code in the CIRC2 sample source code directory.

Suggested Reading

  • , Visual C++ Programmer's Guide

  • , Visual C++ Programmer's Guide

ActiveX Control Properties — An Overview

Properties are typically used to represent control data or attributes. For example, a Date control might define a DateValue property, which provides access to the current date value displayed in the control. This type of property represents control data. In addition, the Date control may define a Format property, which allows the user to get and set the display format of the date. This type of property represents a control attribute.

ActiveX control classes support four types of custom properties:

  • DISP_PROPERTY

    Implemented using a member variable.

  • DISP_PROPERTY_NOTIFY

    Implemented using a member variable and a notification function.

  • DISP_PROPERTY_EX

    Implemented using Get/Set functions.

  • DISP_PROPERTY_PARAM

    Implemented using Get/Set functions and an index parameter.

In the following topics, you will add the CircleShape property, which is an example of a DISP_PROPERTY_NOTIFY custom property. CircleShape is a Boolean property that displays the control as a perfect circle, if set to TRUE; or as an ellipse, if set to FALSE. (The DISP_PROPERTY_EX and DISP_PROPERTY custom property types are used later in the tutorial.)

In this lesson, you will: