Invisible at Runtime Controls

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So, as we have just seen, the ActiveX control is a GUI-based COM object, which may have a set of associated property pages. To put one wrinkle in our current understanding, it is important to note that some controls are "invisible at runtime." These controls are also graphical building blocks at design time.

At run time, the visible interface of the control is hidden from view, while the services it provides churn away in the background. The VB Timer control is an example of such an item (the Timer control is used to capture WM_TIMER messages). At design time, the VB developer sees a visible timer icon on the form, which disappears during execution:


Figure 14-5: An invisible at runtime control.

Now that we have a better grasp of the purpose of an ActiveX control, we will spend the rest of this chapter learning how to create one of our own using the ATL framework. Even though these coclasses are very complex given the functionality they provide, the good news is a typical ActiveX control will make use of just about everything you have learned about COM up to this point. As for the new topics necessary to build a full control, the ATL framework is here to pick up the slack. However, before we begin coding the example control used in this chapter, we need to spend a bit of time getting comfortable with the basic services and additional interfaces used in a typical ActiveX control.



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Developer's Workshop to COM and ATL 3.0
Developers Workshop to COM and ATL 3.0
ISBN: 1556227043
EAN: 2147483647
Year: 2000
Pages: 171

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