Palm webOS

System Services

This section describes each of the system services. Very few of the services apply to the News application, so most of the code samples in this section are simple ones to illustrate the service calls and handlers.

The system services are accessed through Mojo.Service.Request(), or the equivalent scene controller method this.controller.serviceRequest():

Mojo.Service.Request("palm://serviceName", options, requestOptions);

The arguments are described in Chapter 8, but briefly:

serviceName

Is a URI-formatted string that uniquely specifies the service name.

options

Includes the designated method, parameters, and callback functions.

requestOptions

Is either set to true, requesting automatic subscription renewal on error, or an object with a resubscribe property and/or a useNativeParser property.

Warning

Be careful to prevent garbage collection of your service requests. Recall from Chapter 8 that requests made with this.controller.serviceRequest() are garbage-collected and destroyed when the scene is popped. You should use Mojo.Service.Request() to save the request object and handle termination of the request yourself to prevent garbage collection.

Service requests do not complete when you make the call; they are all asynchronous. If it’s possible that the life of your request will outlast the life of the assistant when the call is made, you must use Mojo.Service.Request().

Service Subscriptions

Most system services offer subscriptions, which provide the option of receiving service notifications ...