Igor’s description of the ListView operation is very helpful.
What also confused me about the RadioGroupPage (of the component reference examples in the
Wicket Library) was the use of models with each of the parts, the details of which
are hidden from us in the examples by the use of text-saving alternate
constructors. I’m guessing
that it works something like as follows (confirmation or correction would be
most welcome!):
When we create the ListView,
we give it a java.util.List as a convenience via an
alternate constructor, but this alternate constructor wraps the java.util.List in a wicket List that implements IModel.
However, this IModel object is only used
internally.
When the ListView
creates the ListItem container component for each java.util.List element, the ListItem
is built with its own IModel wrapping the individual java.util.List element.
The populateItem() method over-rides the ListView’s
abstract method in its concrete subclass, and is called to fill each ListItem with subcomponents, providing (among other things)
an IModel for each element added to the ListItem. Typically,
the subcomponent’s model is based on a piece of the ListItem’s
model. For a simple label, for example, we can
call getModelObject() on the ListItem to reach past
the IModel wrapping, and then drill down to the
relevant java.lang.String contained within. We can then allow the Label’s
convenience constructor to wrap the java.lang.String
within an IModel. Alternately, we can construct a PropertyModel for the Label using the ListItem’s
IModel and an OGNL string.
Within a RadioGroup,
the model for each Radio button can be anything that is distinguishable from
the other Radio buttons’ models.
Rather than recording TRUE or FALSE for each Radio button as we would
for Checkbox’s, the framework simply sets the model of the overall RadioGroup to the selected Radio button’s model. (If the RadioGroup
is initialized to have no Radio button selected, we create it with an empty “default”
Model, as this will differ from every Radio button’s model.)
If we create a set of Radio buttons
dynamically based via a ListView, the models for each
ListItem will be distinguishable from one another --
with a 1-to-1 correspondence between ListItem’s
and Radio buttons. Therefore, the
easiest thing to do is to re-use each ListItem’s
IModel as the IModel for its
Radio button, as is done in the RadioGroupPage
example.
Is this the intuition?
-----Original Message-----
From:
[EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
On Behalf Of Igor Vaynberg
Sent: Monday, January 23, 2006
12:45 PM
To:
wicket-user@lists.sourceforge.net
Subject: Re: [Wicket-user]
ListView tutorial?
radiogroup aside
lets take a simple example, we want to show a table of users:
<table>
<tr wicket:id="listview">
<td><span
wicket:id="firstname"/></td><td><span
wicket:id="lastname"/></td>
</tr>
</table>
what we want is everything within <tr>...</tr> to repeat once for
every user. so we attach listview to the tr tag.
what listview does is make its immediate children believe that their markup is
that of the listview itself. so each immediate child believes that it is
attached to the <tr wicket:id="listview"> tag.
we need to represent these immediate listview children with a container
component, because each of these children may contain multiple children of its
own, in our case the firstname/lastname labels. this is what the listitem is,
its a simple WebMarkupContainer created for you so you dont have to do it
everytime youself.
so we will have a listitem container created for every list item in the list
that feeds the lisview. but this is not enough. each of these listitems must
contain the components that represent data within it (the firstname, lastname
labels that we want to add).
this is where populateitem comes in, it is called once for every listitem
created and allows you to add components to it.
so the listview render process looks like this:
before each render:
clear all children
for every list item in the list:
create a ListItem webmarkupcontainer
add created ListItem as a child
call populateItem with the created ListItem container
to allow users to populate it
render:
render all immediate children with own markup
does this help or confuse you more?
-Igor
On 1/23/06, Frank Silbermann < [EMAIL PROTECTED]>
wrote:
Has anyone written about the way ListView works in
Wicket -- i.e. the
roles played by ListView, ListItem and the models belonging to these
components?
I've looked at the JavaDoc in the hope of gaining some intuition as to
what is going on, but I'm having "a difficult time seeing the forest
because of all the trees."
For example, I'm looking at the Component Reference examples,
specifically the RadioGroupPage. The RadioGroup object is
constructed
with "new Model()" -- which leads me to ask myself "What kind of
a silly
model is that?
Looking at the API documentation for RadioGroup, is says that the
group's model is "set to the model of the selected Radio
component." So
I'm guessing that "new Model()" is just a filler to tell the
RadioGroup
NOT to search for a ComponentModel further up the hierarchy -- this
time, the model comes from down lower in the hierarch. (If that's
true,
perhaps this usage of a trivial model ought to be described somewhere in
the RadioGroup JavaDoc. Or is it a more general pattern followed by
a
variety of selection components? Does the JavaDoc for the most
general
abstract selection component explain this usage?)
So I look further down for the Radio objects themselves, and see that
they are created within the populateItem() method of an anonymous
subclass of ListView. Perhaps the relationship between RadioGroup
and
Radio would be more easily understood via a simpler (though less
practical) example in which the set of Radio components were hardcoded
-- my vague understanding of working with Listview is getting in the
way.
As it stands, we give each Radio component the same model as one of the
ListItem components of the ListView. I presume the ListItem is built
from one of the items of the java.util.List from which the ListView was
contructed -- but how???
I suppose my next step is to look at the Wicket implementation of
ListView and ListItem to figure out what is going on.
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