Re: WOComponent children
Re: WOComponent children
- Subject: Re: WOComponent children
- From: Chuck Hill <email@hidden>
- Date: Fri, 4 Jan 2008 17:42:39 -0800
Caveat: I wrote that, but I am not proud of it. That is some nasty
code and I washed my hands after writing it. Twice.
I am working on a response to Aaron, but keep getting distracted.
Chuck
On Jan 4, 2008, at 3:17 PM, Simon McLean wrote:
I know you can do this in WODynamicElement. Here is an example from
Wonder's AjaxTabPanel:
private void findTabs(WODynamicGroup template) {
if (template == null) return;
NSArray children = template.childrenElements();
for (int i = 0; i < children.count(); i++) {
WOElement child = (WOElement)children.objectAtIndex(i);
if (child instanceof AjaxTabbedPanelTab) {
AjaxTabbedPanelTab childTab = (AjaxTabbedPanelTab)child;
// The tabs need to have an id attribute so we assign
one if needed
if (childTab.id() == null) {
childTab.setId(new WOConstantValueAssociation
(id.valueInComponent(null) + "_pane_" + tabs.count()));
}
tabs.addObject(childTab);
}
else if (child instanceof WODynamicGroup) {
findTabs((WODynamicGroup)child);
}
}
}
On 4 Jan 2008, at 23:13, 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).
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.
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. 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.
-- Aaron
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