《GOF设计模式》—迭代器 (ITERATOR)—Delphi源码示例：内部迭代器(封装不同类型的迭代)

示例：封装不同类型的迭代 实现： 内部迭代器可以封装不同类型的迭代。例如，FilteringListTraverser封装的迭代仅处理能通过测试的那些列表元素。这个类接口除了增加了用于测试的成员函数TestItem外与ListTraverser相同,它的子类将重定义TestItem以指定所需的测试。Traverse根据测试的结果决定是否越过当前元素继续遍历。 这个类的一中变体是让Traverse返回值指示是否至少有一个元素通过测试。 代码： unit uFilteringListTraverser; interface uses uList,uListIterator; type     TFilteringListTraverser = class     private         FIterator: TListIterator;     protected         function ProcessItem(AItem: TObject): Boolean; virtual; abstract;         function TestItem(AItem: TObject): boolean; virtual; abstract;     public         constructor Create(AList: TList1);         destructor Destroy; override;         //---         function Traverse(): Boolean;     end; implementation { TFilteringListTraverser } constructor TFilteringListTraverser.Create(AList: TList1); begin     FIterator := TListIterator.Create(AList); end; destructor TFilteringListTraverser.Destroy; begin     FIterator.Free;     //---     inherited; end; function TFilteringListTraverser.Traverse: Boolean; begin     Result := false;     //---     with FIterator do     begin         First;         while not IsDone do         begin             if TestItem(CurrentItem) then             begin                 Result := ProcessItem(CurrentItem);                 if not Result then                     break;             end;             //---             Next;         end;     end; end; end. unit uPrintNEmployees1; interface uses uList,uFilteringListTraverser; type     TPrintNEmployees1 = class(TFilteringListTraverser)     protected         function ProcessItem(AItem: TObject): Boolean; override;         function TestItem(AItem: TObject): boolean; override;     end; implementation uses uEmployee; function TPrintNEmployees1.ProcessItem(AItem: TObject): Boolean; begin     TEmployee(AItem).Print;     Result := true; end; function TPrintNEmployees1.TestItem(AItem: TObject): boolean; begin     Result := Length(TEmployee(AItem).Name) >= 2; end; end. procedure TForm1.Button6Click(Sender: TObject); var     AEmployees: TList1;     pa: TPrintNEmployees1; begin     self.Memo1.Clear;     //---     AEmployees := TList1.Create;     try         with AEmployees do         begin             Add(TEmployee.Create('1',self.Memo1));             Add(TEmployee.Create('22',self.Memo1));             Add(TEmployee.Create('3',self.Memo1));             Add(TEmployee.Create('44',self.Memo1));         end;         //---         pa := TPrintNEmployees1.Create(AEmployees);         pa.Traverse;         pa.Free;     finally         AEmployees.Free;     end; end;