《GOF设计模式》—备忘录（MEMENTO）—Delphi源码示例：一个反映备忘录模式的迭代接口

说明： Dylan中的Collection提供了一个反映备忘录模式的迭代接口。Dylan的集合有一个"状态"对象的概念,它是一个表示迭代状态的备忘录。每一个集合可以按照它所选择的任意方式表示迭代的当前状态；该表示对客户完全不可见。 代码： unit uCollection; interface uses Dialogs,Contnrs; type     TItem = class     private         FValue:string;     public         constructor Create(const AValue:string);         //---         procedure Process();     end;     TIterationState = class     private         FCurrent: Integer;     public         constructor Create;     end;     TCollection = class     private         FList: TObjectList;     public         constructor Create;         destructor Destroy; override;         //---         function CreateInitialState: TIterationState;         function Copy(AState: TIterationState): TIterationState;         //---         procedure Next(AState: TIterationState);         function IsDone(AState: TIterationState): boolean;         function CurrentItem(AState: TIterationState): TObject;         //---         procedure Append(AItem: TObject);         procedure Remove(AItem: TObject);     end; implementation function TCollection.CreateInitialState: TIterationState; begin     Result := TIterationState.Create; end; function TCollection.Copy(AState: TIterationState): TIterationState; begin     Result := TIterationState.Create;     Result.FCurrent := AState.FCurrent; end; constructor TCollection.Create; begin     FList := TObjectList.Create; end; destructor TCollection.Destroy; begin     FList.Free;     //---     inherited; end; function TCollection.CurrentItem(AState: TIterationState): TObject; begin     Result := FList[AState.FCurrent]; end; function TCollection.IsDone(AState: TIterationState): boolean; begin     Result := AState.FCurrent >= FList.Count; end; procedure TCollection.Next(AState: TIterationState); begin     with AState do         FCurrent := FCurrent + 1; end; procedure TCollection.Append(AItem: TObject); begin     FList.Add(AItem); end; procedure TCollection.Remove(AItem: TObject); begin     FList.Remove(AItem); end; constructor TIterationState.Create; begin     FCurrent := 0; end; constructor TItem.Create(const AValue: string); begin     FValue := AValue; end; procedure TItem.Process; begin     ShowMessage(FValue); end; end. procedure TForm3.Button1Click(Sender: TObject); var     ACollection: TCollection;     AState: TIterationState; begin     ACollection := TCollection.Create;     try         with ACollection do         begin             Append(TItem.Create('1'));             Append(TItem.Create('2'));             Append(TItem.Create('3'));             //---             AState := CreateInitialState();             try                 while not IsDone(AState) do                 begin                     TItem(CurrentItem(AState)).Process();                     Next(AState);                 end;             finally                 AState.Free;             end;         end;     finally         ACollection.Free;     end; end; procedure TForm3.Button2Click(Sender: TObject); var     ACollection: TCollection;     AState,AState1: TIterationState; begin     ACollection := TCollection.Create;     try         with ACollection do         begin             Append(TItem.Create('1'));             Append(TItem.Create('2'));             Append(TItem.Create('3'));             //---             AState := CreateInitialState();             try                 while not IsDone(AState) do                 begin                     TItem(CurrentItem(AState)).Process();                     Next(AState);                     //---                     AState1 := Copy(AState);                     try                         while not IsDone(AState1) do                         begin                             TItem(CurrentItem(AState1)).Process();                             Next(AState1);                         end;                     finally                         AState1.Free;                     end;                 end;             finally                 AState.Free;             end;         end;     finally         ACollection.Free;     end; end;