OpenEdge Development: Mobile Applications - Product ...

Chapter 4: Creating Mobile Apps using JSDOs
• Returning data and information from JSDO local storage:
– getData( ) — Called on a JSDO table reference, this method returns an
array of record objects for a referenced temp-table; has no effect on existing
working record settings.
– getId( ) — Called on a JSDO table reference or a JSRecord reference, this
method returns the unique internal record ID for the specified record object;
has no effect on existing working record settings.
– getSchema( ) — Called on a JSDO table reference, this method returns an
array of objects, one for each field, that defines the schema of the referenced
temp-table; has no effect on existing working record settings.
These methods always execute synchronously.
• Managing JSDO event subscriptions:
– subscribe( ) — Subscribes a given event handler function to a named
event on a JSDO or on a JSDO table reference; has no effect on existing
working record settings.
– unsubscribe( ) — Unsubscribes a given event handler function from a
named event on a JSDO or on a JSDO table reference; has no effect on
existing working record settings.
These methods are called on the JSDO or on a JSDO table reference, and
execute synchronously. For more information on JSDO events and managing
JSDO event subscriptions, see the “Asynchronous and synchronous execution”
section on page 98.
Asynchronous and synchronous execution
As described in the previous section, most JSDO methods execute synchronously,
which means that the Mobile App waits for the method to complete execution before
executing the next JavaScript statement or evaluating the next term of an expression.
When method execution completes and returns its results, the Mobile App continues
with the next JavaScript operation.
However, the JSDO fill( ) and saveChanges( ) methods, which execute built-in
Mobile operations, always execute asynchronously, and any non-built-in invocation
methods, which execute non-built-in Mobile invoke operations, execute
asynchronously by default, but can optionally execute synchronously. Asynchronous
execution means that immediately after the Mobile App calls the method, it continues
to execute the next JavaScript statement or to evaluate the next term of an expression.
Results of an asynchronous method execution only become available to the Mobile
App when an event associated with the method fires and an event handler function that
is subscribed to the event executes and receives the results.
98 OpenEdge ® Development: Mobile Applications