Spry User Guide - Support - Adobe

The spry:choose construct provides functionality equivalent to a case statement, or an if-else if-else construct. To
create a spry:choose structure add a spry:choose attributetoanelement.Next,addoneormorechildelements
with spry:when attributes on them. The value of a spry:when attribute should be a JavaScript expression that
returns a zero or nonzero value. To have a default case, in case all of the JavaScript expressions for each spry:when
attribute return zero or false, add an element with a spry:default attribute. The spry:default attribute doesn't
require a value, but XHTML states that all attributes must have a value, therefore, set the value of the attribute equal
to its name.
The region processing engine evaluates the spry:when attribute of each node in the order they are listed under their
parent element. The spry:default elementisalwaysevaluatedlast,andonlyifnospry:when expression returns a
nonzero value.
Region states
Spry supports the notion of region states. That is, at any given time, a region is either loading data, ready to display
the data, or in an error state because one or more of the data sets it is bound to failed to load its data. You can place
a spry:state attribute, with a value of "loading", "error", or "ready" on elements inside aregioncontainerto
associate it with a specific region state. Doing so can be quite useful for displaying a loading message as the data for
aregionloads,ornotifyingtheuserthattheregionfailedtogetitsdata.Astheregionchangesstates,itautomatically
regenerates its code and displays any elements with a spry:state attribute that matches the current state.
The following example uses the spry:state attribute to display loading and error messages:
Loading employee data ...
Failed to load employee data!
{firstname} {lastname}
SPRY
User Guide
Any content that does not have a spry:state attribute on it, or is not a child or descendent of an element that has
a spry:state attribute on it, is always included in the output when the code is regenerated. Also, children or descendents
of an element with a spry:state attributecannothavespry:state attributes. That is, nesting elements with
spry:state attributes is not supported.
Region observer notifications
Spry supports an observer mechanism that allows a developer to register an object or function to receive a notification
whenever the state of a region changes. This mechanism is almost identical to what is used for data sets with
the following exceptions:
• Adding and removing region observers is done through the Spry.Data.Region.addObserver() and
Spry.Data.Region.removeObserver global namespaced functions. This practice is different from data sets
because data set observers call addObserver() and removeObserver() methods that are on the data set object.
The use of global namespaced functionsallowsadevelopertoregisteranobserverbeforethedocument'sonload
event starts, and before Spry creates the JavaScript object that represents the region. Regions use addObserver
and removeObserver functions because the developer might want to register observers before the JavaScript
region object actually exists.
• Both addObserver() and removeObserver() require an ID to identify which region the developer wants to
observe. For this reason, regions that developers want to observe must have an id attribute defined on their region
container node.
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