OpenEdge Development: Mobile Applications - Product ...

Managing JSDO event subscriptions
JSDO overview
You can subscribe event handlers to JSDO events using either the subscribe( )
method on the JSDO or by setting appropriate properties in an initialization object that
you can pass to the constructor to instantiate the JSDO. If you use the subscribe( )
method after the JSDO is instantiated and its local storage has been loaded with
records, you can also subscribe to events for the Mobile create, update, and delete
operations that execute only for a specific table reference.
When you subscribe an event handler function to a JSDO event, the parameter list for
the function must match the parameter list defined for the event. However, every event
handler receives a reference to the JSDO as its first parameter and a reference to a
request object as its last parameter that contains event results (see the following
section). All handlers for 'after*' events receive a Boolean parameter that indicates
the success of the Mobile operation (or operations for 'afterSaveChanges'). All
handlers for events fired by Mobile create, update, and delete operations receive a
JSRecord object parameter that represents the record object in local storage that is
created, updated, or deleted. For more information on the required parameter list for
each event, see the reference entry for the event in Appendix C, “OpenEdge
JavaScript Class Properties, Methods, and Events Reference.”
Regardless of how you subscribe event handlers to an event, you can remove an event
subscription for an event handler using the unsubscribe( ) method. If an event has
no event handler subscribed and the event fires, it returns no results to the Mobile App.
Handling asynchronous and synchronous execution results
For the synchronous JSDO methods (such as add( ) or find( )) that do not execute
Mobile operations, the results for both successful and unsuccessful execution are as
defined for each method. For more information, see the reference entry for the method
in Appendix C, “OpenEdge JavaScript Class Properties, Methods, and Events
Reference.”
For methods that execute Mobile operations asynchronously (fill( ),
saveChanges( ), and invocation methods), the results for each event are returned in
a general request object that is passed as the last parameter to the event handler. For
invocation methods that you execute synchronously, a reference to this same request
object is available as the return value of the method. This request object has a number
of properties whose values depend on the event. Some properties (including the jsdo,
jsrecord, and success properties) duplicate the settings of the other parameters
passed to the event handler. The settings of other properties provide additional
information appropriate for the event.
One of the most important is the response property of the request object. This property
is set only for the 'after*' events of all Mobile operations (that is, all except the
'afterSaveChanges' event). It references a JavaScript object that a Mobile operation
returns for a successful completion or with ABL errors.
For a built-in Mobile operation that completes successfully, this property references a
JavaScript object that contains the data of the returned temp-table or ProDataSet
converted from any valid JSON returned for the operation over the network, and is
otherwise null.
OpenEdge ® Development: Mobile Applications 101