[Seaside] Brushes and state

James Foster Smalltalk at JGFoster.net
Tue Jun 23 16:22:09 UTC 2009


The #children problem is reported by Seaside in the usual manner with  
no extra explanation (see attached).

The idea of passing a block to the was one that I thought of as well.  
I seem to recall that the X Window System had something analogous for  
initializing widgets (I can't lay my hands on any documentation,  
however). On the other hand, it seems to be adding complexity in that  
some things are set one way and some things another way. I'd almost  
prefer everything being done in the block:

MyComponent>>#renderContentOn: html
	html render: (GoogleMap configure: [:map |
			class: 'foo';
			style: 'bar';

Of course, this has the disadvantage of forcing you to use the more  
complex style for everything.

Without harping on the point too much, I'm still not feeling as  
uncomfortable as it seems I should with the Brush approach. One of the  
things mentioned as a characteristic of a Brush is that it can have  
things embedded in it (using #'with:'). There are exceptions already,  
including <br /> and <hr />, so this isn't really a firm rule. Also, a  
GoogleMap makes sense only on an WAHtmlCanvas. While it can create its  
own Canvas, that seems a bit of an additional complexity. I guess I'm  
still seeing HorizontalRule, Button, TextInput, ListBox, and GoogleMap  
as being on a continuum of simple to complex but otherwise not  
substantively different in the way they are created and used. For  
some, embedding other tags makes sense; for others it does not. Most  
can display user-defined data and return new values. Most have events  
that can trigger asynchronous callbacks. All are represented by HTML  
Tags. Some share tags but are distinguished only by the class (input  
button). With the GoogleMap, I could even imagine embedding other  
content that would show if JavaScript were disabled in the browser.

In any case, it seems like several options are available. Maybe if new  
Painters were more familiar, that approach wouldn't seem so different.  
(Okay, having typed that last sentence I see that it isn't very  


On Jun 22, 2009, at 7:24 PM, Julian Fitzell wrote:

> I'm not sure exactly what the issue with #children is, but I know  
> (or at least think I know) that what I posted should work  
> (conceptually) in 2.9. It's possible that stuff isn't quite factored  
> correctly in 2.8 somehow... or it's possible the code I wrote in the  
> email just wasn't quite right.
> There's definitely some extra grayness in this case because what  
> you're rendering is *largely* a div, even though it's more than that  
> and I can see your point about tag attributes. One thing that comes  
> to mind here (don't try this at home, kids, it may yet be a terrible  
> idea) is to give GoogleMap a block that gets passed the div brush  
> during rendering. Would look something like:
> renderContentOn: html
>   html render:
>     (GoogleMap new
>       setCenter: 45.5267 @ -122.8390 zoom: 11;
>       enableGoogleBar;
>       addType: GMapType physical;
>       addControl: GControl largeMapControl;
>       divBlock: [ :div | div class: 'foo'; style: 'bar' ])
> And then GoogleMap would have
> renderContentOn: html
>   div := html div;
>   div
>     doSomeStuff;
>     someMoreStuff.
>   self divBlock value: div.
>   div with: ["you probably don't need this since your div is empty"]
> Now I don't know that this is a good idea nor am I even 100% sure it  
> works but it seems like it should and *could* be a solution to this  
> problem. The problem is of course no different than any other  
> component that has a top-level div that somebody might want to  
> customize the attributes of so it's not unique to your case. Of  
> course, somebody could also just subclass GoogleMap to do that kind  
> of custom styling (as long as it is well-factored) and that may  
> actually be the best option.
> I'm not sure that brushes literally need to only represent HTML spec  
> tags, though TagBrushes certainly lean that way and it may be a good  
> principle to keep an mind as a starting point.
> If you want to provide a walkback on the #children problem I can try  
> to see if it is solvable in 2.8.
> Julian
> On Mon, Jun 22, 2009 at 3:44 PM, James Foster  
> <Smalltalk at jgfoster.net> wrote:
> Julian,
> I've gotten things going with GoogleMap as something other than a  
> Brush or Component (see GoogleMaps-jgf.22.mcz in http://seaside.gemstone.com/ss/GoogleMaps.html) 
> . As an exercise in rendering a generic object, it was certainly  
> useful (I knew of the capability, but hadn't ever done it). My  
> immediate reaction is that it is cleaner in that it _uses_ a brush  
> rather than _is_ a brush. On the other hand, there are some  
> complications.
> With the Brush implementation, there are a number of inherited  
> "features" that just come along. Specifically, I now need to cache  
> any tag-related attributes that the programmer might want to set  
> (such as ID, CLASS, etc.) and put them out. If there were a need for  
> a full implementation, then this could get awkward (for example, I  
> didn't do STYLE, and I don't support generic attributes).
> Also, when I create my own canvas in #'renderOn:' (as suggested by  
> your code just below), callbacks fail because the implementation of  
> #'children' is incomplete. My work-around was to just use the passed- 
> in Renderer, assuming that it supports HTML.
> If the design philosophy is that Brushes represent only things  
> defined in the official HTML spec (which seems reasonable), then the  
> new approach is good enough. I do like this better than making a  
> full Component (which seems heavy-weight).
> Comments?
> James
> On Jun 19, 2009, at 7:51 PM, Julian Fitzell wrote:
>> That should provide a good comparison.
>> Looking at the 2.9 code now I realize it may be hard for you to  
>> simply lift the code because of the refactoring in the way walking  
>> the component tree happens.
>> As a starting point for 2.8, try making GoogleMap subclass Object  
>> and implement something like:
>> renderOn: aRenderer
>>   |html|
>>   html := WAHtmlCanvas
>>     context: aRenderer context
>>     callbacks: (aRenderer context callbacksFor: self).
>>   self renderContentOn: html.
>> I think you should then be able to implement #renderContentOn: to  
>> output your content and allow a GoogleMap to be passed to the  
>> #render: method.
>> That code is untested, just typed into gmail, but it should be  
>> something like that. :)
>> Julian
>> On Fri, Jun 19, 2009 at 4:43 PM, James Foster  
>> <Smalltalk at jgfoster.net> wrote:
>> Julian,
>> I think the only think I'm equipped to give even a weak opinion on  
>> is that as I was doing this some months ago I found a Brush to be  
>> more natural to use (as a client) than a Canvas. As to the relative  
>> merits of Painter and Renderer, I'm just not sufficiently informed  
>> to venture an educated opinion (though that isn't usually an  
>> impediment ;-).
>> I like your point that a Brush can be embedded in another Brush and  
>> this is a feature that the GoogleMap does not need. Given that  
>> sending #with: to a GoogleMap does not make sense, I'll agree that  
>> making it a Brush is a bit awkward. Also, there is a sense in which  
>> subclassing from WADivTag comes back to the question of delegation  
>> vs. inheritance, and in principal I'd prefer delegation.
>> In an effort to contribute more intelligently to this discussion,  
>> I'd like to try refactoring my library using a Painter. I'll fire  
>> up a Seaside 2.9 environment and look at WAPainter with an eye  
>> toward what would be required to refactor my GoogleMap in a Seaside  
>> 2.8 environment.
>> James
>> On Jun 19, 2009, at 12:20 PM, Julian Fitzell wrote:
>>> On Fri, Jun 19, 2009 at 10:50 AM, James Foster <Smalltalk at jgfoster.net 
>>> > wrote:
>>> Julian,
>>> As you were going through this my thought was eventually expressed  
>>> when you said that the painter approach "works essentially the  
>>> same as the brush" approach. And Yes, my updateRoot: code was  
>>> simply an extension to WAComponent that adds some JavaScript.  
>>> Switching it to a class-side method on GoogleMaps as you describe  
>>> would be equivalent and perhaps more obvious and less intrusive.
>>> The part I'm not yet following or seeing much value in is the idea  
>>> that using a different renderer would be desirable. I don't see  
>>> much point of rendering a GoogleMap on anything other than an HTML  
>>> canvas. Or are you envisioning two renderers (HTML for the  
>>> GoogleMap thing and something else for the rest)? At the moment,  
>>> my understanding of the alternate renderers is so shallow that I  
>>> don't see the use/value. For my purposes, at least, I'll probably  
>>> leave my implementation as a Brush subclass since it seems to work  
>>> for all use cases I understand. Which is not to say that I mind  
>>> the discussion!
>>> James,
>>> The discussion is clarifying for me as well so let's carry on... :)
>>> First, I do think your design would be improved slightly by  
>>> putting that method on the class side of GoogleMap.
>>> The idea of having different Renderers is that, for example,  
>>> somebody might eventually decide they'd really like to have  
>>> templates in Seaside and that would probably be implemented as a  
>>> different Renderer. Or maybe they want to embed a google map in a  
>>> Component that is using the RSS Renderer (actually, that Renderer  
>>> still uses Brushes, so it may not be the best example). As I said,  
>>> this is relatively theoretical at the moment given the lack of  
>>> other Renderers but I'm interested in it from the architectural  
>>> angle.
>>> I believe (and this is where I may be wrong) that an  
>>> implementation using Brushes is (slightly) less flexible and,  
>>> while there are things that would be easier using Brushes, I don't  
>>> see that this problem does any of those things.
>>> Or to look at it another way, just as you say that GoogleMap  
>>> doesn't need to *be* a Component but can be rather *used by* a  
>>> Component, I don't think it needs to *be* a Brush but can instead  
>>> *use* a Brush; there's nothing you need to output to the Document  
>>> that can't easily be done with the existing Brushes.
>>> So you might end up with
>>> MyComponent
>>>   (uses)
>>> any Renderer
>>>   (to render a)
>>> GoogleMap (a Painter)
>>>   (which uses its)
>>> HtmlCanvas (a Renderer)
>>>   (to get a)
>>> DivTag (a Brush)
>>>   (which writes to)
>>> HtmlDocument (a Document)
>>>   (which writes to)
>>> Stream
>>> When I say it "works essentially the same as the brush", what I  
>>> mean is, the Painter implementation is equally convenient to use  
>>> and no harder to implement but provides added flexibility. It also  
>>> requires no class method extensions and means you can leverage  
>>> WAScriptTag instead of duplicating stuff to make sure the CDATA is  
>>> added and so on. Since I can't (yet) see an advantage to the Brush  
>>> implementation, my suggestion is that the Painter implementation  
>>> is "more correct" architecturally.
>>> I still think "uses a Brush" (actually two) is a clearer  
>>> relationship for this than "is a Brush" even in 2.8, but without  
>>> Painter there's really no added benefit (though you could easily  
>>> duplicate the very limited amount of functionality Painter has in  
>>> its #renderOn: method and you'd be in the same shape as 2.9).
>>> So the architectural question for me comes down to (sorry for the  
>>> long message), is there an additional benefit to doing it as a  
>>> Brush over a Painter that I'm missing?
>>> Julian
>>> _______________________________________________
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