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Delegating to a class-type property

 

If the delegate property is of a class type, that class and its ancestors are searched for methods implementing the specified interface before the enclosing class and its ancestors are searched. Thus it is possible to implement some methods in the class specified by the property, and others in the class where the property is declared. Method resolution clauses can be used in the usual way to resolve ambiguities or specify a particular method. An interface cannot be implemented by more than one class-type property. For example,

type

  IMyInterface = interface

    procedure P1;

    procedure P2;

  end;

  TMyImplClass = class

    procedure P1;

    procedure P2;

  end;

  TMyClass = class(TInterfacedObject, IMyInterface)

    FMyImplClass: TMyImplClass;

    property MyImplClass: TMyImplClass read FMyImplClass implements IMyInterface;

    procedure IMyInterface.P1 = MyP1;

    procedure MyP1;

  end;

procedure TMyImplClass.P1;

  ...

procedure TMyImplClass.P2;

  ...

procedure TMyClass.MyP1;

  ...

var

  MyClass: TMyClass;

  MyInterface: IMyInterface;

begin

  MyClass := TMyClass.Create;

  MyClass.FMyImplClass := TMyImplClass.Create;

  MyInterface := MyClass;

  MyInterface.P1;        // calls TMyClass.MyP1;

  MyInterface.P2;        // calls TImplClass.P2;

end;

 

Topic groups

 

See also

Implementing interfaces by delegation

Method resolution clause

 

 

译文

 

委托类类型属性

 

如果委托属性是一个类类型，那么在委托属性声明所在的类及其祖先类被搜索之前，将在委托属性所属的类及其祖先类中搜索实现指定接口的方法。（在下面的例子中，委托属性声明所在的类是TMyClass，委托属性所属的类是TMyImplClass。）由此可见，在由属性指定的类中实现一些方法而该类中声明了其他的属性，这是可能的。方法决定子句通常被用于解决不明确或特别指定的方法。接口不能被多于一个类类型属性实现。例如，

type

  IMyInterface = interface

    procedure P1;

    procedure P2;

  end;

  TMyImplClass = class

    procedure P1;

    procedure P2;

  end;

  TMyClass = class(TInterfacedObject, IMyInterface)

    FMyImplClass: TMyImplClass;

    property MyImplClass: TMyImplClass read FMyImplClass implements IMyInterface;

    procedure IMyInterface.P1 = MyP1;

    procedure MyP1;

  end;

procedure TMyImplClass.P1;

  ...

procedure TMyImplClass.P2;

  ...

procedure TMyClass.MyP1;

  ...

var

  MyClass: TMyClass;

  MyInterface: IMyInterface;

begin

  MyClass := TMyClass.Create;

  MyClass.FMyImplClass := TMyImplClass.Create;

  MyInterface := MyClass;

  MyInterface.P1;        //调用TMyClass.MyP1;

  MyInterface.P2;        //调用TImplClass.P2;

end;

 

主题组

 

相关主题

通过委托实现接口

方法决定子句