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The Jifty::Web::Form::* classes are currently a bit of a mess. This is
an effort to document their internals so they make some sense to
whoever finally gets motivates to fix them (which may well be me).
C<Jifty::Web::Form::Element> is the base of *every* class in the
hierarchy. Virtually any widget that Jifty renders, be it a link,
button, or form field, comes from some subclass of
C<Element> itself deals essentially only with writing out javascript
event handlers for widgets. Its <javascript> method walks the
C<onclick> argument to all those buttons and links, building up a data
structure that is eventually serialized using JSON and passed to
jifty.js's C<update> function in an C<onclick=> wrapper.
Form fields (usually created by C<form_field> calls on a
C<Jifty::Action> are all subclasses of C<Jifty::Web::Form::Field>,
C<Field> takes care of most of the work of rendering form fields. It
renders the label, autocompletion, placeholders, hints, validation
errors and warnings, and so on. Subclasses override methods as
appropriate to add or alter details of the rendering. Note that
subclasses need *not* concern themselves with making sure that the
field is rendered as the correct kind of widget (field, select, etc.),
assuming they represent a standard, single, HTML C<input> tag (as
opposed to, say, C<Combobox>). That is dealt with by the C<type>
Whenever you create a C<Field>, it has a C<type>. Normally, this
represents the C<type> property on the C<input> tag. In order to make
the system extensible, however, it *also* indicates what perl class
this widget will be. C<Jifty::Web::Form::Field::new> blesses the
returned object into C<'Jifty::Web::Form::Field::' . ucfirst
$type>. The stock rendering renders an input field with
C<type="$type">, but subclasses can override C<render_widget> to
render something else -- see C<Jifty::Web::Form::Field::Combobox> for
an example of doing this.
Simple links are instances of C<Jifty::Web::Form::Field::Link>. This
class is fairly simple -- it merely renders as a HTML C<a> tag with
the appropriate attributes.
The only detail that remains is the non-javascript state-variable
emulation of AJAX support on links and buttons. This is
C<Jifty::Web::Form::Field::Clickable>'s job. C<Clickable> is also a
C<Element>, which means it inherits the Javascript hooks. Its
constructor builds up a list of state variables that need to be
B<saved> from the previous request, while its C<generate> method walks
the javascript hooks inherited from C<Element> and generates new state
variables that will need to be sent by this button to simulate the
AJAX effects given in the C<onclick>. If the clickable needs to submit
actions, C<generate> creates it as a button, and otherwise it creates
a link. It does this by creating a *new*
C<Jifty::Web::Form::Field::Link> or C<Jifty::Web::Form::Field::Field>
object, and serializing all the state variables it's built up onto
that object appropriately (in the name, if it's a button, as GET
parameters if it's a link).
This final step, where a C<Clickable> (which is not renderable) clones
itself into a different class that can be rendered, makes use of the
C<accessors> method defined in C<Element>. Every subclass of
C<Element> keeps a list of the accessors defined on that class
(typically these are defined using C<Class::Accessor::Fast>, but not
always). When C<Clickable> needs to clone itself, it walks the list
C<< ($self->accessors) >>, building up a hash of all the accessor
key-value pairs on itself, and passes these to C<new> on C<Field> or
C<Link>, which calls accessors on itself for every C<key => value>
pair in its argument list.
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