Hello,
Wouldn't it better to make Canvas protected and pass it on the OnPaint event? I'm almost sure is was also public in Delphi, and I don't even remember Delphi having OnPaint in TCustomControl, but... BTW why is OnPaint called inside TCustomControl.Paint instead of TCustomControl.PaintWindow?

Best regards,
Fl?vio

Fl?vio Etrusco wrote

Hello, Wouldn't it better to make Canvas protected and pass it on the OnPaint event?

Yes. It seems a Delphi compatible design

I'm almost sure is was also public in Delphi,

Yes it is.

and I don't even remember Delphi having OnPaint in TCustomControl,

Yes Delphi does not has.

IMHO it does not makes sense since TCustomControl is not supposed to be used directly. It's supposed to be derived and override Paint. The same for SetColor. Color should not be public so not handled by default in TCustomControl.

but... BTW why is OnPaint called inside TCustomControl.Paint instead of TCustomControl.PaintWindow?

PaintWindow -> Paint -> OnPaint

Luiz

I forgot
http://docwiki.embarcadero.com/VCL/XE/en/Controls.TCustomControl.Paint

Luiz

I guess you mean the current behavior is as it is for Delphi compatibility, right?
I supposed so, but isn't it worth changing?

I kind of agree; that must be the reasoning for Borland. OTOH I realize it can be quite useful for quick hacks, like painting a background image. It'd be even more useful there pre- and post- events hardcoded in PaintWindow. I vote for Painting and Paint, respectively ;-)

I know, but it'd be better be invoked by/in PaintWindow so that all controls have consistent behavior and component implementors don't have to remember to call 'inherited'.

-Fl?vio

TCustomControl is to be a base class not for quick hacks. Adding more functions would blow the code for most components that don't use it

OnPaint can be even undesired in some controls

If some descendants needs OnPaint is pretty simple to add with the benefit of choosing where to call.

As an example see
http://code.google.com/p/luipack/source/browse/trunk/cairo/lcl/cairolcl.pas#86

OnPaint and SetColor are not necessary here just blow code

like painting a background image. It'd be even more useful there pre- and post- events hardcoded in PaintWindow. I vote for Painting and Paint, respectively ;-)

I would keep a lean base class. Even i would remove onpaint and setcolor altogether

Anyway, since TCustomControl is not a visual control and you need those features, you can create easily an descendant and use it as base for your components

Luiz

(...) TCustomControl is to be a base class not for quick hacks. Adding more functions would blow the code for most components that don't use it

Oh my. I suppose it's not be used directly in TCustomControl, but on descendants.

OnPaint can be even undesired in some controls If some descendants needs OnPaint is pretty simple to add with the benefit of choosing where to call.

This is not in question. It's already there.

-Fl?vio

2011/7/14 Fl?vio Etrusco :

I guess you mean the current behavior is as it is for Delphi compatibility, right? I supposed so, but isn't it worth changing?

No, there are many component sets which work with both the VCL and the LCL. Creating incompatibilities generates problems for component developers. Note that TCustomControl is a basic building block for component developers.

Making things that are protected in Delphi public in Lazarus is not a problem, but the opposite is a big compatibility problem.

What about descendants that dont use it? Dont need it?

Yes but is useless. Even delphi does not has.

For an descendant overriding Paint is easier then assigning an OnPaint handler. And the descendant may not want to expose OnPaint to users case when will just be using extra memory

Luiz

Accessing Canvas outside Paint in Windows isn't recommended, but works. It doesn't on other platforms, and we've seen in the ML several people falling in this trap, didn't we?

-Fl?vio