Delphi类和方法。需要为多个类实现一个方法

Question

举个例子，我给一个农场安排了蔬菜班。

TVegetable = class

TCarrot = class(TVegetable)
TTomato = class(TVegetable)

我需要两种不同种类的蔬菜，一种用于超市，另一种用于工厂。

TCarrotSupermarket = class(TCarrot)
TCarrotFactory = class(TCarrot)

除了一个方法的代码之外，这些类都是相同的：

procedure Utilization;

TCarrotSupermarket.Utilization与超市合作，TCarrotFactory.Utilization与工厂合作。

我需要一个相同的Utilization代码用于TCarrotSupermarket.Utilization、TTomatoSupermarket.Utilization、TPotatoSupermarket.Utilization，另一个代码用于TCarrotFactory.Utilization、TTomatoFactory.Utilization、TPotatoFactory.Utilization。

只为Utilization编写两次代码(对于超市和工厂)并在适当的类中使用它的最佳方式是什么？

Answer 1

欢迎使用Pattern Design。你的案例是Strategy patternn

class TStrategyVegetable = class(TVegetable)
  FUtil: TUtilization
public
  procedure Create(util: TUtilization);
  procedure Utilization();
end

procedure TStrategyVegetable.Create(util: TUtilization)
begin
  FUtil := util
end
procedure TStrategyVegetable.Utilization;
begin
  FUtil.Utilization;
end

然后在代码中：

carrotSupermarket = TCarrotSupermarket.Create(TCarrotSupermarketUtil.Create);
carrotFactory = TCarrotFactory.Create(TCarrotFactoryUtil.Create);

Answer 2

下面是使用接口方法解析解决方案的一些伪代码。(未经测试，甚至没有编译，但它应该会为您指明正确的方向)

IFactoryInterface=interface(IUnknown) ['{someGUID}']
  procedure Utilization;
end;

ISuperMarketInterface=interface(IUnknown) ['{AnotherGUID}']
  procedure Utilization;
end;

TVegetable = class (TSomeObject,IFactoryInterface,ISupermarketInterface)
protected
  // the routines tha do the actual implementation
  // can be regular virtual, dynamic, or whatever
  procedure FactoryUtilization; 
  procedure SuperMarketUtilization; 
  // link up the interfaces using method resolution
  procedure IFactoryInterface.Utilization=FactoryUtilization;
  procedure ISupermarketInterface.Utilization=SuperMarketUtilization;

{ in case not derived from TInterfacedObject, 
  You'll have to add _AddRef,_Release and 
  QueryInterface methods too }

end;

// the other implementations can be as before
TCarrot = class(TVegetable)
TTomato = class(TVegetable)

然后，当使用代码时，它应该看起来像这样：

VAR lSOmeVegetable,lAnotherVegetable:TVegetable;
... 
lSomeVegetable:=TCarrot.Create
lanotherVegetable:=Tomato.Create
...
// call using buolt-in type checking
(lSOmeVegetable as IFactoryInterface).Utilization;
(lAnotherVegetable as ISuperMarketInterface).Utilization;

或以其他方式使用support例程

VAR lFactory:IFactoryInterface;
...
if supports(lSomeVegetable,IFactoryInterface,lFactory) then
  lFactory.Utilization
...

希望这能对你有所帮助。这里有一个指向一些匹配的documentation的指针