The following diagram is an overview of the Visual Component Library (VCL) that shows the major branches of the inheritance tree.
The Borland Component Library for Cross-Platform (CLX) looks very much the same at this level although TWin Control is replaced by TWidget Control. Signifies the base class and ultimate ancestor of everything in the VCL or CLX.
TObject encapsulates the fundamental behavior common to all VCL/CLX objects by introducing methods that perform basic functions such as creating, maintaining, and destroying an instance of an object.
TComponent is the common ancestor of all components.
This class allows a component to be displayed on the Component palette, lets the component own other components, and allows the component to be manipulated directly on a form.
Represents the base class for all controls that are visible at runtime.
TControl is the common ancestor of all visual components and provides standard visual controls like position and cursor.
The following diagram is a greatly simplified view of the inheritance hierarchy that illustrates the relationship between objects, components, and controls.
Objects, components, and controls Every object inherits from TObject, and many objects inherit from TComponent.Controls inherit from TControl and have the ability to display themselves at runtime.A control like TCheck Box inherits all the functionality of TObject, TComponent , and TControl, and adds specialized capabilities of its own.This class also provides events that respond to mouse actions.Several controls let you customize the way the control is rendered.These include list boxes, combo boxes, menus, headers, tab controls, list views, status bars, tree views, and toolbars. Indicating that a control is owner-drawn To customize the drawing of a control, you must supply event handlers that render the control's image when it needs to be painted. For example, list views, tree views, and toolbars all receive events at various stages in the drawing process without your having to set any properties.