Instances of C++ classes representing windows, dialog boxes, and controls are called interface objects.

Interface objects are actually inside application objects. An interface object is an ObjectWindows class that is created and stored on the application's heap or stack, depending on how the object is allocated. The interface element, on the other hand, is actually a part of Windows. It is the actual window that is displayed on the screen.

Interface Objects?

One of the greatest difficulties of Windows programming is that controlling interface elements can be inconsistent and confusing. Sometimes you send a message to a window; other times you call a Windows API function. The conventions for similar types of operations often differ when those operations are performed with different kinds of elements. ObjectWindows alleviates much of this difficulty by providing objects that encapsulate the interface elements. This insulates you from having to deal directly with Windows and provides a more uniform interface for controlling interface elements.

Do Interface Objects Do?

An interface object provides member functions for creating, initializing, managing, and destroying its associated interface element. The member functions manage many of the details of Windows programming for you. Interface objects also encapsulate the data needed to communicate with the interface element, such as handles and pointers to child and parent windows. The relationship between an interface object and an interface element is similar to that between a file on disk and a C++ stream object. The stream object only represents an actual file on disk; you manipulate that file by manipulating the stream object. With ObjectWindows, interface objects represent the interface elements that Windows itself actually manages. You work with the object, and Windows takes care of maintaining the Windows element.