Defining the Component Interface
Before you can create the component for your dialog box, you need to decide how you want developers to use it. You create an interface between your dialog box and applications that use it.
For example, look at the properties for the common dialog box components. They enable the developer to set the initial state of the dialog box, such as the caption and initial control settings, then read back any needed information after the dialog box closes. There is no direct interaction with the individual controls in the dialog box, just with the properties in the wrapper component.
The interface must therefore contain enough information that the dialog box form can appear in the way the developer specifies and return any information the application needs. You can think of the properties in the wrapper component as being persistent data for a transient dialog box.
In the case of the About box, you do not need to return any information, so the wrapper's properties only have to contain the information needed to display the About box properly. Because there are four separate fields in the About box that the application might affect, you will provide four string-type properties to provide for them.