| Description |
The Published directive starts a declaration section of a class definition. In a published section, Fields, Properties and Methods are declared to be accessible to this class, classes descending from it, and code using object instances of the class. And information about these accesses are recorded in the run time information for the class.
In Object Oriented terms, a class object is seen as a black box. The internal operations are not relevant. Public and published fields, properties and methods are the externally visible part of an object - a controlled access to the internals of the class.
Because public and published access provides a linkage of sorts to external code, you should avoid wherever possible making changes to these sections.
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| Notes |
Warning : avoid making fields published - it is always better to define a property to access them instead. This provides some decoupling from the internals of the class.
Only one Constructor may be declared as published - overloaded versions must be defined as public.
Published properties cannot return arrays.
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| Related commands |
| Function |
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Defines a subroutine that returns a value |
| Private |
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Starts the section of private data and methods in a class |
| Procedure |
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Defines a subroutine that does not return a value |
| Property |
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Defines controlled access to class fields |
| Protected |
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Starts a section of class private data accesible to sub-classes |
| Public |
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Starts an externally accessible section of a class |
| Type |
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Defines a new category of variable or process |
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| Example code : A simple example |
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
unit Unit1;
interface
uses
Forms, Dialogs, Classes, Controls, StdCtrls, SysUtils;
type
// Define a base TSquare class :
TSquare = class
private // Only known internally
squareArea, squareWidth, squareHeight : Integer;
Published // Known externally : has run time info also
property width : Integer read squareWidth;
property height : Integer read squareHeight;
property area : Integer read squareArea;
constructor Create(width, height : Integer);
end;
// Define the form class used by this unit
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm} // Include form definitions
// Create the TSquare object
constructor TSquare.Create(width, height: Integer);
begin
// Save the width and height
squareWidth := width;
squareHeight := height;
// And calculate and save the square area
squareArea := width * height;
end;
// Main line code
procedure TForm1.FormCreate(Sender: TObject);
var
mySquare : TSquare;
begin
// Create a square object
mySquare := TSquare.Create(30, 40);
// What are the square attributes ? :
ShowMessageFmt('Square area = %d * %d = %d',
[mySquare.width, mySquare.height, mySquare.area]);
end;
end.
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Square area = 30 * 40 = 1200
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