Is CSS the best metaphor for styling for a UIToolkit? Maybe not

Writing your own UI Toolkit is, if nothing else, educational. As the OpenPyro framework continues to evolve, every time a new feature is added, I look around at prior art in the domain and evaluate the choices made by different frameworks which has been fascinating. Of course, the first framework I look at (since I have had most experience with that) has always been Flex (both Flex 3 and 4 separatly since they are so different), but often I do compare that with choices made by the IPhone’s UIKit, HTML/CSS and (rarely) Swing or any of the Java toolkits.

One of the features that I know I will need to add in a future version will be a simpler way to style/skin the controls. OpenPyro controls are based around composition so creating new UI assets and passing them in as skin elements is simple enough but there is always a need to do something simpler. A blue scrollbar for example shouldn’t need blue assets, more the ability to tell the scrollbar to draw itself with a stroke/fill of blue color.

Flex’s choice in this domain has been CSS and thats not surprising. A lot of the way Flex was developed was to enable it to be a gateway drug to ActionScript for developers from other technology domains and who doesn’t know CSS? Flex 3’s CSS capabilities were very basic and I keep reading how Flex 4’s CSS engine is so much more complete. And considering how much easier it is to create a Flex 3 theme compared to a Look and Feel in Swing, that seems to have been a decent choice. Someone recently asked when OpenPyro would support that functionality which led to this post.

I have often found writing CSS for Flex a chore, for most of the reasons I find writing CSS rules boring: complete loss of any logic system. Deep in ActionScript land while developing an application, switching to CSS is irritating. Suddenly I am in a file where I cannot really code any logic or rules. One of the first libraries of ActionScript I wrote over 3 years back had explicitly defined style objects. For example, ScrollBars would have a corresponding ScrollBarStyle class that listed all style properties. Being a pure AS class, I could also code logic in that, so conditionally apply style properties because I could inspect the properties of the UI element the style was being applied to. Heck, I could even get code hinting of relevant styles for a particular component.

What spurred this post today was seeing how the engineering team I work with at Comcast Interactive Media adopting the Less CSS engine. I have personally not worked with this yet but I might in a coming sprint. By accounts so far, its awesome to work with and I completely don’t doubt that. Most of the logic here seems something that you can write pretty easily in pure AS3 classes and pass them around as something equivalent to Flex/Javascript’s CSSStyleDeclaration object (link to JS CSSStyleDeclaration object)

Anyway, the point of this post was, while CSS may be the most familiar styling metaphor, there may be better ones. I hope OpenPyro can probably adopt something more powerful like lessCSS rather than pure CSS.

Update: Another flavor of a *better CSS* system: SASS

Update 2: Smashing Magazine has a pretty good writeup on CSS ideas and debates. More food for thought as I spec out a styling language for OpenPyro.

Is CSS the best metaphor for styling for a UIToolkit? Maybe not

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