[Seaside] Brushes and state
Julian Fitzell
jfitzell at gmail.com
Fri Jun 19 01:13:10 UTC 2009
So, with the need to update the root, I think this would work equally well
as a simple renderable object in 2.8 but it wouldn't really be be much
better than a component or brush.
With a 2.9 Painter, you can implement #updateRoot: on the
Painter subclass itself so the map object would be able to encapsulate
all of that. This does require, as you point out, that the Painter be
added to #children, of course, but I think that's better than having
to implement your own root updating behaviour and not unexpected for
the user.
Your renderContentOn: would look basically the same as your version with
either a painter or a renderable object:
MyComponent>>#renderContentOn: html
html render: (GoogleMap new
class: 'myMap';
setCenter: 45.5267 @ -122.8390 zoom: 11;
"..."
yourself)
So I think the result is slightly better with a Painter in the sense of
implementing #children, rather then update root behaviour.
The other advantage is more theoretical and that is that a painter is not
dependent on the encapsulating component using Canvas as its renderer. I say
this is pretty theoretical because the only other renderer right now is the
RSS one. :) From an architectural point of view, though, components are able
to use any renderer they want and if they're using one that doesn't support
your brush, well they couldn't easily use your implementation.
This is all pretty subtle. Thus the debate. :)
Julian
On Thu, Jun 18, 2009 at 5:49 PM, James Foster <Smalltalk at jgfoster.net>wrote:
> Julian,
>
> I did the GoogleMaps stuff several months ago and was only comparing
> component and brush; I didn't consider a Painter mostly from lack of
> knowledge (and being on a 2.8 environment). I wasn't aware that there was a
> debate about when to use brushes; I thought it was just me who couldn't
> figure it out!
>
> I ended up with a Brush because it felt more like I was just defining a
> special <div> and I didn't want to require people to define a child
> component. I figured that until I needed something more complicated I'd stay
> with the simplest thing that could possibly work (tm), and the brush
> approach came together nicely. Once I started thinking about GoogleMaps as
> being little more than a fancy div/listbox/image, several things fell out
> quite cleanly. I discovered that I don't want to keep any state and that I
> want to treat the configuration as one does with other things. For example
> (where all of the messages to the brush are optional, but #setCenter:zoom:
> is most useful):
>
> MyComponent>>#renderContentOn: html
>
> html googleMap
> class: 'myMap';
> setCenter: 45.5267 @ -122.8390 zoom: 11;
> enableGoogleBar;
> addType: GMapType physical;
> addControl: GControl largeMapControl;
> setUIToDefault;
> on: 'zoomEnd' do: [:x :y :z |
> 'alert("Zoom from ' , x printString , ' to ' , y
> printString ,
> ' (see GMUsingLatLong>>renderContentOn:)");'];
> yourself.
>
> The only other requirement is that the component needs to allow some
> #updateRoot: behavior:
>
> MyComponent>>#updateRoot: anHtmlRoot
>
> super updateRoot: anHtmlRoot.
> self updateRootWithGoogleMaps: anHtmlRoot.
>
> The implementation involves creating various scripts and feeding them out,
> but it works fine in the brush.
>
> GoogleMap>>#with: anObject
>
> self ensureId.
> super with: [
> anObject renderOn: canvas.
> canvas html: self mapScript.
> ].
> self addLoadScript: self variable , 'Init()'.
>
> Overall it seemed less intrusive for the library client to use a brush
> rather than a component. Other than #updateRoot:, there isn't really much to
> do. With a component there were so many things that were brush-like,
> including setting the class, id, style, etc., and more issues (does it need
> to be included as a child?). I was able to do so much without state, that it
> just seemed nice this way. It seemed like I got further than any of the
> other GoogleMaps packages I found, but I'd love to see another approach or
> get expert feedback on what I've done.
>
> In general, while I'm heavily involved in Seaside from the GemStone
> point-of-view, there is still a great deal for me to learn about when to use
> different parts of the framework. This exercise was another opportunity to
> learn and I did learn something!
>
> James
>
>
> On Jun 18, 2009, at 5:15 PM, Julian Fitzell wrote:
>
> James,
>>
>> It's been a while since I looked at the google maps stuff so I don't
>> recall... what do you actually render to the page? If memory serves, you
>> only need to output stuff that can be generated by the standard brushes
>> (divs and JS or something, right?) and you don't need to put content inside
>> it.
>>
>> I have no memory of whether there is anything that requires a component to
>> keep state but it doesn't *seem* at first glance to me like something that
>> needs to be a brush either. I don't mean to suggest you're wrong since
>> you've obviously gone through the exercise and I haven't but there's quite a
>> bit of debate now and then over when to use brushes. I'm just wondering
>> whether you considered a renderable object (a Painter in 2.9) as an option
>> or just component/brush. And if you ruled out the third option, is there a
>> particular reason you think a brush is more appropriate?
>>
>> Julian
>>
>> On Thu, Jun 18, 2009 at 4:00 PM, James Foster <Smalltalk at jgfoster.net>
>> wrote:
>> Mariano,
>>
>> I'll be interested to see how this comes out. As I mentioned earlier, I
>> started with a component and switched to a brush. I came to view the
>> GoogleMap as a browser widget, something like a listbox, where you give it
>> some data and let it draw itself. Yes, you can configure callbacks, but that
>> isn't really different from other brushes. What sort of 'state' do you
>> envision keeping with the map? Might that be better in a domain-specific
>> component that wraps a map? I was able to implement over 40 examples and
>> have not yet found a need to get more complex.
>>
>> James
>>
>> On Jun 18, 2009, at 2:58 PM, Mariano Montone wrote:
>>
>> Thanks Julian. I think a component will be ok.
>>>
>>> Mariano
>>>
>>> On Thu, Jun 18, 2009 at 1:22 PM, Julian Fitzell <jfitzell at gmail.com>
>>> wrote:
>>> Hi Mariano,
>>>
>>> Off the top of my head, if I were implementing a google maps package, I
>>> would do it as a component or a painter (see below). Brushes certainly
>>> aren't intended to be kept around so if you have state to persist between
>>> requests that's not the way to go.
>>>
>>> There are people who like implementing everything as brushes but the main
>>> functionality of brushes is that they can be selected in arbitrary orders to
>>> nest content within each other, e.g.:
>>>
>>> html div: [ html span: [ html paragraph: 'foo' ] ].
>>>
>>> Unless you plan to do be able to do:
>>>
>>> html div: [ html googleMap: [ html paragraph: 'foo' ] ]
>>>
>>> (i.e. unless the thing you are creating allows content to be put inside
>>> it) I don't think there's much advantage in making your own brush. (The
>>> other reason to consider using brushes of course is that they have more
>>> direct access to the document).
>>>
>>> Even if you don't need the benefits of components (see
>>> http://blog.fitzell.ca/2009/05/when-to-use-seaside-component.html ), you
>>> can just create a renderable object by implementing #renderOn: and do:
>>>
>>> html render: (GoogleMaps new configSomeStuff; yourself)
>>>
>>> This process is made much clearer in 2.9 where you can subclass
>>> WAPainter, implement #rendererClass to control what kind of renderer you get
>>> passed (you might possibly implement the google maps thing *using* one or
>>> more custom brushes and have your own renderer for them), and implement
>>> #renderContentOn: as you would for a component.
>>>
>>> Hopefully that makes things clearer and not muddier. :)
>>>
>>> Julian
>>>
>>> On Thu, Jun 18, 2009 at 5:51 AM, Mariano Montone <
>>> marianomontone at gmail.com> wrote:
>>> Hello!,
>>> I'm implementing an API for rendering Google Maps. I've decided
>>> to implement it as a brush. That's because I'm just generating javascript
>>> code. But now I have a problem: when adding support for callbacks, I need to
>>> hold some state; for example, the map the callback refers to. But I think
>>> brushes are not meant to hold state, that is something left for the
>>> components mechanism, isn't it? So I would like to know what would be the
>>> correct way of implementing it in the framework. Should I implement maps as
>>> components, or should I add state to my brushes; I may hold a state in the
>>> callback block too, but I don't think that's good.
>>>
>>> Thanks!
>>>
>>> Mariano
>>>
>>>
>>>
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