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10-8 Delphi Language Guide
Implementing interfaces
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;
ƒ
procedure TMyImplClass.P2;
ƒ
procedure TMyClass.MyP1;
ƒ
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;