示例：迭代器接口 说明： （1）、定义 提供一种方法顺序访问一个聚合对象中各个元素,而又不需暴露该对象的内部表示。 （2）、结构 迭代器： Iterator（迭代器）：迭代器定义访问和遍历元素的接口。 ConcreteIterator（具体迭代器）：具体迭代器实现迭代器接口。对该聚合遍历时跟踪当前位置。 聚合： Aggregate（聚合）：聚合定义创建相应迭代器对象的接口。 ConcreteAggregate（具体聚合）：具体聚合实现创建相应迭代器的接口，该操作返回ConcreteIterator的一个适当的实例。 协作： ConcreteIterator跟踪聚合中的当前对象，并能够计算出待遍历的后继对象。 代码： unit uIterator1; interface uses SysUtils,Classes,Dialogs; type TConcreteAggregate = class; TIterator = class public procedure First(); virtual; abstract; procedure Next(); virtual; abstract; function IsDone(): Boolean; virtual; abstract; function CurrentItem(): string; virtual; abstract; end; TConcreteIterator = class(TIterator) private FAggregate: TConcreteAggregate; FCurrent: integer; public constructor Create(const Aggregate: TConcreteAggregate); //--- procedure First(); override; procedure Next(); override; function IsDone(): Boolean; override; function CurrentItem: string; override; end; TAggregate = class public function CreateIterator(): TIterator; virtual; abstract; end; TConcreteAggregate = class(TAggregate) private FList:TStringList; function GetCount: integer; function GetItems(Index: integer): string; public constructor Create; destructor Destroy; override; //--- function CreateIterator: TIterator; override; procedure Add(s:string); //--- property Count: integer read GetCount; property Items[Index: integer]: string read GetItems; default; end; procedure Test; implementation procedure Test; //--- procedure _ShowAggregate(I:TIterator); begin I.First; while not I.IsDone do begin ShowMessage(I.CurrentItem); I.Next; end; end; var Aggregate: TConcreteAggregate; AIterator: TIterator; begin Aggregate := TConcreteAggregate.Create; try with Aggregate do begin Add('111'); Add('222'); Add('333'); end; //--- AIterator := Aggregate.CreateIterator; _ShowAggregate(AIterator); AIterator.Free; finally Aggregate.Free; end; end; constructor TConcreteIterator.Create(const Aggregate: TConcreteAggregate); begin FAggregate := Aggregate; FCurrent := 0; end; procedure TConcreteIterator.First; begin FCurrent := 0; end; procedure TConcreteIterator.Next; begin FCurrent := FCurrent + 1; end; function TConcreteIterator.IsDone: Boolean; begin Result := FCurrent >= FAggregate.Count; end; function TConcreteIterator.CurrentItem: string; begin if self.IsDone then raise Exception.Create('Iterator Out Of Bounds'); //--- Result := FAggregate.Items[FCurrent]; end; constructor TConcreteAggregate.Create; begin FList := TStringList.Create; end; destructor TConcreteAggregate.Destroy; begin FList.Free; //--- inherited; end; function TConcreteAggregate.CreateIterator: TIterator; begin Result := TConcreteIterator.Create(self); end; function TConcreteAggregate.GetCount: integer; begin Result := FList.Count; end; function TConcreteAggregate.GetItems(Index: integer): string; begin Result := FList[Index]; end; procedure TConcreteAggregate.Add(s: string); begin FList.Add(s); end; end.
