Delphi 设计模式：《HeadFirst设计模式》Delphi7代码---迭代器模式之DinerMenu

 

      容器的主要职责有两个：存放元素和浏览元素。根据单一职责原则（SRP）要将二者分开，于是将浏览功能打包封装就有了迭代器。

      用迭代器封装对动态数组的遍历：

 

1.容器中的元素类

{《HeadFirst设计模式》之迭代器模式 } { 容器中的元素类 } { 编译工具：Delphi7.0 } { E-Mail ：[e-mail] } unit uItem; interface type TMenuItem = class(TObject) private FName: String; FDescription: String; FVegetarian : Boolean; FPrice: Double; public constructor Create(aName, aDescription: String; aVegetarian : Boolean; aPrice: Double); function GetName: String; function GetDescription: String; function GetPrice: Double; function IsVegetarian: Boolean; end; implementation { TMenuItem } constructor TMenuItem.Create(aName, aDescription: String; aVegetarian: Boolean; aPrice: Double); begin FName := aName; FDescription := aDescription; FVegetarian := aVegetarian; FPrice := aPrice; end; function TMenuItem.GetDescription: String; begin Result := FDescription; end; function TMenuItem.GetName: String; begin Result := FName; end; function TMenuItem.GetPrice: Double; begin Result := FPrice; end; function TMenuItem.IsVegetarian: Boolean; begin Result := FVegetarian; end; end.

 

2.迭代器

{《HeadFirst设计模式》之迭代器模式 } { 迭代器：封装对容器的遍历 } { 编译工具：Delphi7.0 } { E-Mail ：[e-mail] } unit uIterator; interface uses uItem; type TMenuItems = array of TMenuItem; TIterator = class(TObject) public function HasNext: Boolean; virtual; abstract; function Next : TObject; virtual; abstract; end; TDinerMenuIterator = class(TIterator) private FMenuItem : TMenuItem; FMenuItems: TMenuItems; FPosition : Integer; public constructor Create(MenuItems: TMenuItems); function HasNext: Boolean; override; function Next : TObject; override; end; implementation { TDinerMenuIterator } constructor TDinerMenuIterator.Create(MenuItems: TMenuItems); begin FMenuItems := MenuItems; end; function TDinerMenuIterator.HasNext: Boolean; begin if (FPosition < Length(FMenuItems)) and (FMenuItems[FPosition] <> nil) then Result := True else Result := False; end; function TDinerMenuIterator.Next: TObject; begin FMenuItem := FMenuItems[FPosition]; FPosition := FPosition + 1 ; Result := FMenuItem; end; end.

3.容器类

{《HeadFirst设计模式》之迭代器模式 } { 容器类及其用户： Waitress } { 编译工具：Delphi7.0 } { E-Mail ：[e-mail] } unit uAggregate; interface uses SysUtils, uItem, uIterator; type TMenu = class(TObject) public function CreateIterator: TIterator; virtual; abstract; end; TDinerMenu = class(TMenu) private FMenuItem : TMenuItem; FMenuItems: TMenuItems; FNumberOfItems: Integer; public constructor Create; destructor Destroy; override; procedure AddItem(aName, aDescription: String; aVegetarian: Boolean; aPrice: Double); function CreateIterator: TIterator; override; end; TWaitress = class(TObject) private FMenuItem : TMenuItem; FDinerMenu: TDinerMenu; DinerIterator: TIterator; public constructor Create(aDinerMenu: TDinerMenu); procedure PrintMenu; overload; procedure PrintMenu(aIterator: TIterator); overload; end; implementation const MAX_TIMES = 6; { TDinerMenu } procedure TDinerMenu.AddItem(aName, aDescription: String; aVegetarian: Boolean; aPrice: Double); begin FMenuItem := TMenuItem.Create(aName, aDescription, aVegetarian, aPrice); if FNumberOfItems >= MAX_TIMES then Writeln('Sorry, menu is full! Can''t add item to menu') else begin FMenuItems[FNumberOfItems] := FMenuItem; FNumberOfItems := FNumberOfItems + 1; end; end; constructor TDinerMenu.Create; begin SetLength(FMenuItems, MAX_TIMES); AddItem('Vegetarian BLT', 'Fakin Bacon with lettuce & tomato on whole Wheat', True, 2.99); AddItem('BLT', 'Bacon with lettuce & tomato on whole Wheat', False, 2.99); AddItem('Soup of the day', 'Soup of the day, with a side of potato salad', False, 3.29); AddItem('Hotdog', 'A hot dog, with saurkraut, relish, onions, topped with cheese', False, 3.05); AddItem('Steamed Veggies and Brown Rice', 'Steamed vegetables over brown rice', True, 3.99); AddItem('Pasta', 'Spaghetti with Marinara Sauce, and a slice of sourdough bread', True, 3.89); end; destructor TDinerMenu.Destroy; begin FreeAndNil(FMenuItem); inherited; end; function TDinerMenu.CreateIterator: TIterator; begin Result := TDinerMenuIterator.Create(FMenuItems); end; { TWaitress } constructor TWaitress.Create(aDinerMenu: TDinerMenu); begin FDinerMenu := aDinerMenu; end; procedure TWaitress.PrintMenu; begin try DinerIterator := FDinerMenu.CreateIterator; Writeln('MENU'); Writeln('----'); Writeln('BREAKFAST'); Writeln; PrintMenu(DinerIterator); finally FreeAndNil(DinerIterator); end; end; procedure TWaitress.PrintMenu(aIterator: TIterator); begin while (aIterator.HasNext) do begin FMenuItem := (aIterator.Next) as TMenuItem; Writeln(FMenuItem.GetName + ','); Writeln(FMenuItem.GetPrice, ' -- '); Writeln(FMenuItem.GetDescription); end; end; end.

4.客户端

{《HeadFirst设计模式》之迭代器模式 } { 客户端 } { 编译工具：Delphi7.0 } { E-Mail ：[e-mail] } program pMenuTestDrive; {$APPTYPE CONSOLE} uses SysUtils, uItem in 'uItem.pas', uAggregate in 'uAggregate.pas', uIterator in 'uIterator.pas'; var DinerMenu: TDinerMenu; Waitress : TWaitress; begin DinerMenu := TDinerMenu.Create; Waitress := TWaitress.Create(DinerMenu); Waitress.PrintMenu; FreeAndNil(DinerMenu); FreeAndNil(Waitress); Readln; end.

运行结果：