Hi,
[I'm posting this here, seeing that I got no response from the FPC
Users mailing list. I guess nobody there uses Interfaces.]
I'm pretty new to using interfaces... I want to use interfaces so that
I can spot problems at compile time and not runtime. For example: If
I used a base class with abstract methods and then created descendant
classes. Now if I forgot to implement one of the abstract methods which gets
called somewhere... I'll only find the problem at runtime (with an
abstract error) and not
compile time.
I would rather like to be told about this problem at compile time. I'm
hoping that Interfaces will solve this issue. Am I allowed to do the
following?
With my preliminary testing this seems to work. As soon as I leave out
one of the IWindowImpl interface methods from the TX11Window class,
the compiler complains. Exactly what I want. :-)
Also can I let my base class descend from TComponent instead of
TInterfacedObject? Looking at the declaration of the TComponent class,
it implements IUnknown, so I guess I am allowed to add more interfaces
in descendant classes.
type
IWindowImpl = interface;
IWindowImpl = interface(IInterface)
['{BDBC9BE7-77E0-4EA1-B40B-282CE06A32B3}']
procedure DoAllocateWindowHandle(AParent: IWindowImpl);
procedure DoSetWindowTitle(const ATitle: string);
end;
TBaseImpl = class(TComponent)
private
FHeight: integer;
FWidth: integer;
procedure SetHeight(const AValue: integer);
procedure SetWidth(const AValue: integer);
public
property Width: integer read FWidth write SetWidth;
property Height: integer read FHeight write SetHeight;
end;
TX11Window = class(TBaseImpl, IWindowImpl)
protected
procedure DoAllocateWindowHandle(AParent: IWindowImpl);
procedure DoSetWindowTitle(const ATitle: string); // leaving this
out would give a compiler warning. Yes!
end;
Aside from my initial question, Is there any things I need to watch
out for? Things being garbage collected before I am actually done with
them, etc..
Regards,
- Graeme -
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