Design Paddern Singelton - Oder wie verstecke ich Create?

[TheFrog]

Hallo Tobi,

im Modelmaker kann ich bestimmte Pattern auf Klassen anwenden, u.a. das Singleton-Pattern, welches folgendermassen implemetiert wird:

Delphi-Quellcode:

unit Singleton;

interface

uses
  SysUtils, Windows, Messages, Classes, Graphics, Controls, Forms, Dialogs;

type
  TSingleton = class(TObject)
  protected
    constructor CreateInstance;
    class function AccessInstance(Request: Integer): TSingleton;
  public
    constructor Create;
    destructor Destroy; override;
    class function Instance: TSingleton;
    class procedure ReleaseInstance;
  end;


implementation

{
********************************** TSingleton **********************************
}
constructor TSingleton.Create;
begin
  inherited Create;
  raise Exception.CreateFmt('Access class %s through Instance only',
      [ClassName]);
end;

constructor TSingleton.CreateInstance;
begin
  inherited Create;
end;

destructor TSingleton.Destroy;
begin
  if AccessInstance(0) = Self then AccessInstance(2);
  inherited Destroy;
end;

class function TSingleton.AccessInstance(Request: Integer): TSingleton;

  {$WRITEABLECONST ON}
  const FInstance: TSingleton = nil;
  {$WRITEABLECONST OFF}

begin
  case Request of
    0 : ;
    1 : if not Assigned(FInstance) then FInstance := CreateInstance;
    2 : FInstance := nil;
  else
    raise Exception.CreateFmt('Illegal request %d in AccessInstance',
        [Request]);
  end;
  Result := FInstance;
end;

class function TSingleton.Instance: TSingleton;
begin
  Result := AccessInstance(1);
end;

class procedure TSingleton.ReleaseInstance;
begin
  AccessInstance(0).Free;
end;



end.

Ich arbeite immer mit diesem Ansatz und finde es klappt recht gut.

Hans.