unit Observer_Pattern;

interface
uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs, System.Generics.Collections,Contnrs;

  //Beobachter
  type TObservers = class(TObject)
     public
       procedure Update; virtual;
     private
  end;

  type TSuject = class(TObject)
    public
       procedure AddObservers(Beobachter : TObservers); virtual; abstract;
    protected
       procedure NoitfyAllObserver; virtual; abstract;
  end;


   type TConcreteSubject = class(TSuject)
     private
       FObserverList : TList<TObservers>;
       FState : Integer;
     public
       procedure AddObservers(Beobachter : TObservers );override;
       procedure SetState(State : Integer);
       function GetSate : Integer;
       constructor Create;
       destructor Destroy;override;
     protected
        procedure NoitfyAllObserver; override;
  end;


  type TConcreteObserver = class(TObservers)
     private
       FConcreteObserver : TConcreteSubject;
     public
       procedure ConcreteObserver(ConcreteSubjec: TConcreteSubject);
       procedure Update; override; abstract;
  end;

implementation


{ TConcreteSubject }

 procedure TConcreteSubject.AddObservers(Beobachter : TObservers);
 begin
   FObserverList.Add(Beobachter);
 end;

 constructor TConcreteSubject.Create;
 begin
   inherited;
   FState := 0;
   FObserverList := TList<TObservers>.Create;
 end;

destructor TConcreteSubject.Destroy;
begin
  FreeAndNil(FObserverList);
end;

 function TConcreteSubject.GetSate: Integer;
 begin
   Result := FState;
 end;

procedure TConcreteSubject.NoitfyAllObserver;
 var Beobachter : TObservers;
 begin
   try
     Beobachter := TObservers.Create;
     for Beobachter in FObserverList do
     begin
       Beobachter.Update;
     end;
   finally
     FreeAndNil(Beobachter);
   end;
 end;

 procedure TConcreteSubject.SetState(State: Integer);
 begin
    FState := State;
    NoitfyAllObserver;
 end;

 {TObservers}

 procedure TObservers.Update;
 begin

 end;

procedure TConcreteObserver.ConcreteObserver(ConcreteSubjec: TConcreteSubject);
var Test : TObservers;
begin
   try
     Test := TObservers.Create;
     FConcreteObserver := ConcreteSubjec;
     FConcreteObserver.AddObservers(Test);
   finally
     FreeAndNil(Test);
   end;
end;


end.