Tony Sinclair wrote ...
> Hi all,
>
> Is it possible to have a constructor for the parent class that receives a
> parameter which determines the type of child that is instantiated in it's
> place?
You could try creating a 'factory' class whose sole
responsibility is to manufacture descendants of another
class (my favourite use/misuse of a design pattern. :) )
For example, say you had the following hierarchy, and
any coloured widget might be required at runtime:
TColouredWidget = class( TObject );
TBlueWidget = class( TColouredWidget );
TRedWidget = class( TColouredWidget );
TGreenWidget = class( TColouredWidget );
The factory class could be
something like:
type
TWidgetColour = (wcBlue, wcRed, wcGreen);
TWidgetFactory = class(TObject)
public
class function CreateColouredWidget( WidgetColour: TWidgetColour ):
TColouredWidget;
end;
implementation
class function TWidgetFactory.CreateColouredWidget( WidgetColour:
TWidgetColour ): TColouredWidget;
begin
case WidgetColour of
wcBlue: Result := TBlueWidget.Create;
wcRed: Result := TRedWidget.Create;
wcGreen: Result := TGreenWidget.Create;
end;
end;
... and could be called thus:
Widget := TWidgetFactory.CreateColouredWidget( WidgetColour );
Is this similar to what you're after?
Cheers,
Cory.
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