Delphi 之Inherited详解

inherited就是调用祖先类的函数，如果不带参数就是默认调用同名函数
如果带参数则表明子类中的函数个数可能比祖先类要多取其中的几个参数传过去
例如
祖先类有个函数 Create(AName:string);
子类有个函数 Create(AName:string;AComponent:TObject);override;
那么子类的Create函数内就可以这样调用祖先类：
procedure TAClass.Create(AName:string;AComponent:TObject);
begin
    Inherited Create(AName);
end;

 

 

 

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

 

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