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Re: Extending CSSOM Views matchMedium with callback

From: Kenneth Christiansen <kenneth.christiansen@openbossa.org>
Date: Mon, 10 May 2010 14:44:37 -0300
Message-ID: <AANLkTinJIsoJh42tZpPZhqc_TBRd6mkybURG3CFiXlpG@mail.gmail.com>
To: Simon Fraser <smfr@me.com>
Cc: "L. David Baron" <dbaron@dbaron.org>, Luiz Agostini <luiz.agostini@openbossa.org>, public-webapps@w3.org, www-style@w3.org
Hi Simon,

So what you are suggesting is a kind of
document.addMediaRuleListener(mediaquery, listener) etc? I think that
should be quite easy to implement.

Kenneth

On Mon, May 10, 2010 at 2:27 PM, Simon Fraser <smfr@me.com> wrote:
> On May 10, 2010, at 8:48 AM, L. David Baron wrote:
>
>> On Friday 2010-05-07 15:31 -0300, Luiz Agostini wrote:
>>> The consensus on the W3C Extending CSSOM Views matchMedium with
>>> callbacks [1] mailing list was that instead of adding individual DOM
>>> events for changes to media features, we should instead make it
>>> possible to get notified when a user defined media query has changed.
>>>
>>> The idea was making it possible to supply a JavaScript function to the
>>> styleMedia.matchMedium(...) function.
>>>
>>> As no exact IDL was proposed, I came up with one myself which I think fits the
>>> use-case, and implemented the feature for WebKit.
>>>
>>> The result of my work became the following IDL, for which I would like
>>> comments/feedback:
>>>
>>>    interface MediaChangeListener {
>>>        void mediaChanged(in boolean queryResult);
>>>    };
>>>
>>>    interface StyleMedia {
>>>        readonly attribute DOMString type;
>>>        boolean matchMedium(in DOMString mediaquery, in MediaChangeListener
>>> listener);
>>>    };
>>
>> This seems reasonable to me, although I wonder if it's worth passing
>> a little more information to the listener, such as (a) the original
>> query or (b) the window.  Would that be useful to authors, or are
>> they comfortable stuffing whatever is necessary in a closure?
>
> This simple callback-based mechanism suffers from various problems (of the type
> that add/removeEventListener were designed to solve):
>
> 1. Unclear behavior when calling matchMedium() a second time for the same query,
> with a different callback.
> 2. No way to remove a callback
> 3. Lack of context on the callback
>
> I also think that forcing authors to call matchMedium() just in order to get callbacks
> when media queries change is not ideal.
>
> It feels to me like the correct solution would be enhance CSS OM somehow to allow
> authors to attach event listeners to CSSMediaRules somehow, so they can get notified
> when those @media statements start or stop matching.
>
> Simon

-- 
Kenneth Rohde Christiansen
Technical Lead / Senior Software Engineer
Qt Labs Americas, Nokia Technology Institute, INdT
Phone  +55 81 8895 6002 / E-mail kenneth.christiansen at openbossa.org
Received on Monday, 10 May 2010 17:45:14 GMT

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