Re: WOComponent children
Re: WOComponent children
- Subject: Re: WOComponent children
- From: Chuck Hill <email@hidden>
- Date: Fri, 4 Jan 2008 21:05:42 -0800
And continuing on...
On Jan 4, 2008, at 3:13 PM, email@hidden wrote:
Hello,
How can I get the children of a WOComponent? More importantly, all
children and all descendants?
WOComponents seem to only know how to go up the tree (find their
parents).
Don't fight the source. ;-)
If you ask a WOComponent for its template (which is roughly
its .html/.wod structure), you can then *almost* ask the template
to go down the tree for its children as WOComponents. This is not
straightforward because as far as I can tell, you got to do a lot
of "cursor incrementing" and tricky instantiation of WOComponents.
Not only do you have to deal with the "template" but you must also
consider a "_childTemplate" for when you've got WOComponentContent
and WOComponentReference objects. I've got some code now that
doesn't quite work because on a complex page it gets the bindings
confused when I try to push a WOComponentReference into context.
I've asked a similar question about a day ago on the WOnder list,
but I've learned a bit more and realize it may be more appropriate
to ask the question here. So sorry if this appears to be a bit of
deja vu for those who read both lists but it's actually a bit more
than that. If you read the earlier message, please disregard it as
I believe this one is more meaningful.
Consider the following code snippet offered by Mr. Rentzsch:
http://www.wodeveloper.com/omniLists/webobjects-dev/2002/July/
msg00246.html
I got so excited when I saw this only to find out that this example
only works in the trivial case, when you don't have any
WOComponentContent such as a PageWrapper component. To make it work
in the general case appears to be very tricky and also inefficient.
Yes, it gets interesting when you go beyond the simple case.
The reason why I'm doing this is because I'm trying to bootstrap a
phase into the request-response loop. In any given reuseable
subcomponent I'm designing, I want to be able to simply implement
"addRequiredWebResources(WOResponse, WOContext)". Inside this
method I would make calls that would examine the HTML response
content and insert multiple lines between the HTML head tags. For
example, CSS file resources and Javascript file resources. This way
I don't need monolithic CSS and JS files but can break the files
down and associate them with the reusable components that need
them. When a page is rendered to the user, only the necessary JS
and CSS resources are referred to in the link and import statements
of the head tag, automatically.
For this to work fully, appendToResponse() must go first so that we
have some "head" tags to discover. But before appendToResponse() is
done, it needs to call "addRequiredWebResources()" on every
possible subComponent in the tree... *every* one of them. This
means it needs to contact even those subComponents that are inside
of WOConditional containers that evaluated to false.
There, I think you might hit a brick wall. If WOConditional
evaluates to false, the contents essentially do not exist. You will
also have trouble with things like WOSwitchComponent.
So yes, there would be many components whose "appendToResponse()"
was not called but "addRequiredWebResources()" was in fact called.
Before the world of partial page refreshes via AJAX and other
means, none of this mattered. But now, because I can refresh a
portion of the screen and show a previously missing "coolWidget"
subComponent that requires "coolLib.js" I'm in trouble. Problem is,
in a partial page refresh, there is no "head" tag so "coolWidget"
will fail horribly because "coolLib.js" is not referenced between
the head tags of the page. In a full page refresh (before the Web
2.0 era) there is no problem because the head tag is readily
available. Get the picture?
I really need some advice here or a sample of how to get to all the
children and children's children of the outmost WOComponent.
Conceptually it would also be interesting to understand why Apple
only exposes the "parent" relationship of a WOComponent. When you
*really* think about it, it makes a lot of sense to get to your
children and not so much to get to the parent. Obviously internally
WebObjects knows how to get to the children, otherwise
appendToResponse won't work. You kind of need to know how to get to
the guys underneath you. Every time I think about the "parent"
relationship the usefulness of it smacks of *clever*. Like maybe
executing the action of a parent WOComponent. But once you do
something like that, you've heavily tied the subComponent to the
parent and it no longer becomes reuseable. Think of a car tire.
That tire should work no matter what car I put it on. I should be
able to pull it from one truck and place it on another without a
care in the world. If the tire wants to let us know that its air
pressure is low then it would just shout "airPressureLow()" and the
right components of the car should be registered to listen to that
message, so there is no need to get to the "parent()".
I fear, without an adequate answer to the question of "how do I get
to my children", our beloved tool of choice can no longer provide
truely reusable WOComponents for the Web 2.0 era.
It is regrettable, but I don't think it can. There is no way to know
all possible states of the page when it is first rendered. You can
probably get past the WOConditional problem, but I can't see any way
past data driven decisions like WOSwitchComponent. Your (very
desirable) wish "This way I don't need monolithic CSS and JS files
but can break the files down and associate them with the reusable
components that need them." seems particularly unlikely.
Chuck
--
Practical WebObjects - for developers who want to increase their
overall knowledge of WebObjects or who are trying to solve specific
problems.
http://www.global-village.net/products/practical_webobjects
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