《GOF设计模式》—观察者（OBSERVER）—Delphi源码示例：推模型(push model)

示例：推模型(push model) 说明： 目标向观察者发送关于改变的详细信息,而不管它们需要与否。 代码： unit uPushModel; interface uses   SysUtils, Classes, Dialogs; type     TSubjectState = record         A,B:Integer;     end;     TObserver = class;     TSubject = class     private         FObservers: TList;         FState: TSubjectState;     public         constructor Create;         destructor Destroy; override;         //---         procedure Attach(AObserver: TObserver);         procedure Detach(AObserver: TObserver);         procedure Notify;     end;     TConcreteSubject = class(TSubject)     private         function GetA: Integer;         function GetB: Integer;         procedure SetA(const Value: Integer);         procedure SetB(const Value: Integer);     public         property A: Integer read GetA write SetA;         property B: Integer read GetB write SetB;     end;     TObserver = class     public         procedure Update(AState: TSubjectState); virtual; abstract;     end;     TConcreteObserver = class(TObserver)     protected         FSubject: TSubject;     public         constructor Create(ASubject: TSubject);         destructor Destroy; override;         //---         procedure Update(AState: TSubjectState); override;     end; procedure Test; implementation procedure Test; var     ASubject: TConcreteSubject;     AObserver: TObserver; begin     ASubject := TConcreteSubject.Create;     AObserver := TConcreteObserver.Create(ASubject);     try         ASubject.A := 1;         ASubject.B := 2;         ASubject.Notify;     finally         AObserver.Free;         ASubject.Free;     end; end; constructor TSubject.Create; begin     FObservers := TList.Create; end; destructor TSubject.Destroy; begin     FObservers.Free;     //---     inherited; end; procedure TSubject.Attach(AObserver: TObserver); begin     FObservers.Add(AObserver); end; procedure TSubject.Detach(AObserver: TObserver); begin     FObservers.Remove(AObserver); end; procedure TSubject.Notify; var     i: integer; begin     with FObservers do     begin         for i := 0 to Count - 1 do             TObserver(Items[i]).Update(FState);     end; end; constructor TConcreteObserver.Create(ASubject: TSubject); begin     FSubject := ASubject;     if FSubject <> nil then FSubject.Attach(self); end; destructor TConcreteObserver.Destroy; begin     if FSubject <> nil then FSubject.Detach(self);     //---     inherited; end; procedure TConcreteObserver.Update(AState: TSubjectState); begin     ShowMessage(IntToStr(AState.A + AState.B)) end; function TConcreteSubject.GetA: Integer; begin     Result := FState.A; end; function TConcreteSubject.GetB: Integer; begin     Result := FState.B; end; procedure TConcreteSubject.SetA(const Value: Integer); begin     FState.A := Value; end; procedure TConcreteSubject.SetB(const Value: Integer); begin     FState.B := Value; end; end.