Observer Pattern

From YYpBD's MediaWiki

목차 1 개요 2 예제 2.1 Delphi 2.1.1 Subject 2.1.2 Observer 2.1.3 이용 2.2 Java 2.2.1 Subject 2.2.2 Observer 2.2.3 이용

개요

Observer 패턴은 정보 제공자인 Subject와 정보 수신자인 Observer로 구성된다.

신문의 예를 들자면 신문을 찍어내는 신문사는 Subject, 신문을 구독하는 독자는 Observer가 된다.

예제

Delphi

Subject

type
  ISubject = interface
    procedure registerObserver(AObserver: IObserver );
    procedure removeObserver( AObserver: IObserver );
    procedure notifyObservers();
  end;

  TNews = class( TInterfacedObject, ISubject )
  private
    FList: TList;
    FData: Integer;
  public
    constructor Create;
    destructor Destroy; override;

    procedure registerObserver(AObserver: IObserver);
    procedure removeObserver(AObserver: IObserver);
    procedure notifyObservers();

    procedure SetData( AData: Integer );
  end;

implementation

{ TNews }

constructor TNews.Create;
begin
  FList := TList.Create;
end;

destructor TNews.Destroy;
begin
  FList.Free;
end;

procedure TNews.notifyObservers;
var
  I: Integer;
  Observer: IObserver;
begin
  for I := 0 to FList.Count - 1 do
  begin
    Observer := IObserver(FList.Items[I]);

    Observer.Update( FData );
  end;
end;

procedure TNews.registerObserver(AObserver: IObserver);
begin
  if FList.IndexOf( Pointer(AObserver) ) = -1 then
    FList.Add( Pointer(AObserver) );
end;

procedure TNews.removeObserver(AObserver: IObserver);
var
  I: Integer;
begin
  for I := 0 to FList.Count - 1 do
  begin
    if FList.Items[I] = Pointer(AObserver) then
    begin
      FList.Delete(I);

      Break;
    end;
  end;
end;

procedure TNews.SetData(AData: Integer);
begin
  FData := AData;

  notifyObservers;
end;

Observer

type
  IObserver = class
    procedure Update( AData: Integer ); virtual; abstract;
  end;

  TReaderDisplay = class( IObserver )
  public
    procedure Update( AData: Integer ); override;
  end;

implementation

{ TReaderDisplay }

procedure TReaderDisplay.Update(AData: Integer);
begin
  // AData를 이용..
end;

이용

var
  FNews: TNews;
  FReaderDisplay: TReaderDisplay;
begin
  FNews := TNews.Create;
  FReaderDisplay := TReaderDisplay.Create;

  FNews.registerObserver( FReaderDisplay );
  FNews.SetData( 20 );
  FNews.removeObserver( FReaderDisplay );

  FNews.Free;
  FReaderDisplay.Free;

Java

Subject

public interface ISubject {
 
	public abstract void registerObserver(IObserver AObserver);
	public abstract void removeObserver(IObserver AObserver);
	public abstract void notifyObservers();
}


import java.util.ArrayList;

public class TNews implements ISubject {
	private ArrayList FObserverList;

	private int FData;

	public TNews (){
	    FObserverList = new ArrayList();
	}

	public void SetData(int AData) {
	    this.FData = AData;
	    
	    OnDataChanged();
	}

	public void OnDataChanged() {
	    notifyObservers();
	}

	public void registerObserver(IObserver AObserver) {
	    if( this.FObserverList.indexOf( AObserver ) < 0 )
    	    this.FObserverList.add( AObserver );
	}

	public void removeObserver(IObserver AObserver) {
	    int Index = this.FObserverList.indexOf( AObserver );
	    if( Index >= 0 )
	        this.FObserverList.remove( Index );
	}
	
	public void notifyObservers() {
	    for( int i = 0; i < this.FObserverList.size(); i++ )
	    {
	        IObserver observer = (IObserver)this.FObserverList.get( i );
	        observer.Update( FTemp, FHumidity, FPressure );
	    }
	}
}

Observer

public interface IDisplayElement {
 
}

public interface IObserver {
	public abstract void Update( int AData );
}


public class TReaderDisplay implements IDisplayElement, IObserver {
	public void Update( int AData ) {

		// AData 이용	 
	}
	 
}
 

이용

    TNews News = new TNews();
    ReaderDisplay = new TReaderDisplay();
    News.registerObserver( ReaderDisplay );

    News.SetData( 10 );