Mega Code Archive
Inherited - used to call the parent class constructor or destructor method
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1 Create;
begin
Inherited; // Always call at the start of a constructor
...
end;
2 Create(arguments);
begin
Inherited Create(arguments); // Always call at the start of a constructor
...
end;
3 Destroy;
begin
...
Inherited; // Always call at the end of a destructor
end;
Description
The Inherited keyword is used to call the parent constructor or destructor method, as appropriate, for the current class.
It is called at the start of a constructor, and at the end of a desctructor. It is not mandatory, but recommended as good practice.
Without parameters, Inherited calls the same named method the parent class, with the same parameters.
You can call a different parent method, if appropriate.
Related commands
Class Starts the declaration of a type of object class
Constructor Defines the method used to create an object from a class
Destructor Defines the method used to destroy an object
Function Defines a subroutine that returns a value
Object Allows a subroutine data type to refer to an object method
Overload Allows 2 or more routines to have the same name
Override Defines a method that replaces a virtual parent class method
Procedure Defines a subroutine that does not return a value
Example code : Examples of Inherited with and without explicit parent method names
// 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;
type
// Define a parent class, base on TObject by default
TFruit = class
public
name : string;
Constructor Create; overload; // This constructor uses defaults
Constructor Create(name : string); overload;
end;
// Define a descendant types
TApple = class(TFruit)
public
diameter : Integer;
published
Constructor Create(name : string; diameter : Integer);
end;
// The class for the form used by this unit
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
end;
var
Form1: TForm1;
implementation
{$R *.dfm} // Include form definitions
// Create a fruit object - parameterless version
constructor TFruit.Create;
begin
// Execute the parent (TObject) constructor first
Inherited; // Call the parent Create method
// Now set a default fruit name
self.name := 'Fruit';
end;
// Create a fruit object - parameterised version
constructor TFruit.Create(name: string);
begin
// Execute the parent constructor first
Inherited Create; // Call the parent Create method
// And save the fruit name
self.name := name;
end;
// Create an apple object
constructor TApple.Create(name: string; diameter : Integer);
begin
// Execute the parent (TFruit) constructor first
Inherited Create(name); // Call the parent method
// Now save the passed apple diameter
self.diameter := diameter;
end;
// Main line code
procedure TForm1.FormCreate(Sender: TObject);
var
fruit : TFruit;
banana : TFruit;
apple : TApple;
begin
// Create 3 different fruit objects
fruit := TFruit.Create;
banana := TFruit.Create('Banana');
apple := TApple.Create('Pink Lady', 12);
// See which of our objects are fruits
if fruit Is TFruit then ShowMessage(fruit.name +' is a fruit');
if banana Is TFruit then ShowMessage(banana.name +' is a fruit');
if apple Is TFruit then ShowMessage(apple.name +' is a fruit');
// See which objects are apples
if fruit Is TApple then ShowMessage(fruit.name +' is an apple');
if banana Is TApple then ShowMessage(banana.name +' is an apple');
if apple Is TApple then ShowMessage(apple.name +' is an apple');
end;
end.
Fruit is a fruit
Banana is a fruit
Pink Lady is a fruit
Pink Lady is an apple
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