Programming Delphi

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 TCheckBox inherits all the functionality of TObject, TComponent
, and TControl, and adds specialized capabilities of its own.

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 TWinControl is replaced by TWidgetControl.

Simplified object hierarchy. 

Class Description
TObject 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.
Exception Specifies the base class of all classes that relate to exceptions. Exception provides a consistent interface for error conditions, and enables applications to handle error conditions gracefully.
TPersistent Specifies the base class for all objects that implement properties. Classes under TPersistent deal with sending data to streams and allow for the assignment of classes.
TComponent Specifies the base class for all nonvisual components such as TApplication. 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. 
TControl 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. This class also provides events that respond to mouse actions. 
TWinControl Specifies the base class of all user interface objects. Controls under TWinControl are windowed controls that can capture keyboard input. In CLX, these are called widgets, and TWidgetControl replaces 

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Programming - Delphi