[Seaside] Brushes and state
Julian Fitzell
jfitzell at gmail.com
Fri Jun 19 15:44:59 UTC 2009
Hm... yes, you're right it would need to be in an instance variable... I had
forgotten about that.
I may have to go back and look at that... I intended Painter to be useable
as a throw-away object. Along the way, updateRoot: got pulled up because it
didn't have any dependencies on anything further down the class hierarchy
but updateRoot: just can't work unless it gets called and currently that is
via the #children mechanism unless you want to call it yourself.
So I'm not sure whether it's better to push #updateRoot: back down to
WAPresenter or leave it on WAPainter with the caveat that if the painter
uses updateRoot: it needs to be listed in #children. The latter seems to add
a confusing ambiguity. Could also split WAPainter into two classes but
that's starting to get a little excessive, I think. Back to the architecture
design board for a bit... (opinions appreciated)
Forgetting updateRoot: then for a second, though, you could still implement
simply with a Painter or renderable object by having a class-side method
that does the root modification.
MyComponent>>updateRoot: aRoot
super updateRoot: aRoot.
GoogleMaps updateRoot: aRoot.
MyComponent>>#renderContentOn: html
html render: (GoogleMap new class: 'myMap';
setCenter: 45.5267 @ -122.8390 zoom: 11;
"..."
yourself)
With that pattern, I think any object that implements #renderOn: now works
essentially the same as a brush? Assuming the root updating is not
component-specific (you don't show what's in it but I gather it's a class
extension on Component added by your package?). WAPainter adds the benefit
that the component doesn't have to be using the same Renderer that
GoogleMaps expects (which the other two options depend on).
Julian
On Fri, Jun 19, 2009 at 7:11 AM, James Foster <Smalltalk at jgfoster.net>wrote:
> Julian,
> Just to clarify your example a bit, let me know if I'm on the right track
> here... With a 2.9 Painter if you need to implement #updateRoot: then you
> need to be in the parent's #children. To be in the parent's children, you
> probably need to be in an instance variable and you probably need to be set
> up in the parent's #initialize method. Thus, your example below of creating
> the map during #renderContentOn: would not work.
>
> To use a Painter or Component: (1) add an instance variable to the parent
> for each map; (2) initialize each instance variable in #initialize; (3) add
> each instance variable to #children; and (4) use the map in
> #renderContentOn:.
>
> To use a Brush: (1) add one message send to your #updateRoot: for any
> number of maps; and (2) add any number of maps in #renderContentOn:.
>
> Given that the map itself does not need any state, creating it as a
> component (I'm not familiar with the painter implications) seems to
> encourage reuse by inheritance rather than by delegation.
>
> I mention these issues to describe my understanding and invite help, not to
> argue. I agree that the distinctions are a bit subtle and I don't need there
> to be a clear "right" answer.
>
> James
>
> On Jun 18, 2009, at 6:13 PM, Julian Fitzell wrote:
>
> 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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