In VCL (Visual Component Library) hierarchy, you will find TObject at the
top, then TPersistent, then TComponent and then TControl.
TObject >> TPersistent >> TComponent >>TControl
VCL Hierarchy in Delphi |
TObject is the base class from which all classes descend.
TPersistent class descends directly from TObject. The
special characteristic of TPersistent is that it is an abstract class that
defines the methods that allow it to be streamed.
TComponent is the base class from which all components
descend. Non-visual components are descendants of TComponent. For example:
TTimer
TControl is the base class from which all the visual components descend. For example: TEdit, TListBox, TComboBox etc.
Again, there are two types of controls (TControl): Window Controls
(TWinControl) and Graphic Controls (TGraphicControl)
Following is the difference between TWinControl and
TGraphicControl in Delphi:
TWinControls
TWinControls can receive input focus and they can be parents to
other controls.
Example: TEdit, TListBox and TComboBox
TGraphicControl
TGraphicControls differ from TWinControls in that they cannot
receive input focus. Also, they cannot be parents to other controls.
Example: TLabel
TGraphicControls are used when you want to display something
on the form.
Two key advantages of TGraphicControls over TWinControls:
1. TGraphicControls don't use up system resources since they
don't require a window handle.
2. They are a bit faster at drawing than their TWinControl
counterparts since their painting is not subject to the windows message
dispatching system. Instead, they piggyback on their parent's paint process.
For more details, please refer to documentation.
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