[Laszlo-dev] Adding default style attribute values

[Henry Minsky]

OK this sounds like a promising approach.




On Wed, Oct 7, 2009 at 11:50 AM, P T Withington <ptw at pobox.com> wrote:

>
> See my reply to myself about a better approach, where you will see that
> despite the $style bindings being classified as 'constraints' they do not
> actually install any delegates (unless the CSS itself specifies a
> constraint, as in, the `attr()` value, which ties one CSS value to another),
> they are just evaluated at initialization time. Also, in the revised
> implementation, we have a 'fallback' or 'default-default', where if there is
> no CSS property found, you install that default instead.  I guess you could
> consider that fallback to specify the default LFC stylesheet, but I don't
> think we have to actually implement any such thing.
>
> Also, the idea is that these are defaults that will be overridden by
> subclasses and instances.  Only if the subclasses and instances do not
> specify values will these defaults be consulted.  But, yes, if we go crazy
> and make every possible attribute CSS styleable, there will be an increase
> in the instantiation time of a view, so we should be judicious about what we
> make styleable in this way.
>
> The goal here is that we think users expect to be able to use CSS to style
> their applications, but because we don't have any default bindings for
> <view> attributes, the user has to do this all by hand.  This way, there
> will be default bindings all set up and they can just add a stylesheet.
>
> We should obviously evaluate the overhead of this change.  There are
> already some pretty good caches that optimize the CSS lookup, but perhaps we
> can make a further optimization that creates a cache on the class to avoid
> re-looking up (non-existen) default CSS bindings for each instance of the
> class.
>
> Finally, someday we _will_ have to have at least one more delegate for each
> instance that has CSS style bindings so that we can implement dynamic CSS
> styles.  I.e., when the user wants to change a stylesheet dynamically and
> see the change propagate to all the views with attributes bound to the
> changed style.  We'd need at least one delegate to re-evaluate the style
> bindings when the style sheets change.
>
>


-- 
Henry Minsky
Software Architect
hminsky at laszlosystems.com
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