DelphiBasics
Inherited
Keyword
Used to call the parent class constructor or destructor method
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
 Author links

 Buy Website Traffic at
 Buywebsitetrafficexperts.com

 Buy Proxies at
 Buyproxies.io
 
 Download this web site as a Windows program.




 
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
 
Delphi Programming Neil Moffatt 2002 - 2017. All rights reserved.  |  Home Page