PG2

28 Chapter 2 PhoneGap Development, Testing, and Debugging
API availability, a web developer building PhoneGap applications must instruct
the container to notify the web application when the PhoneGap APIs are available.
Any application processing that requires the use of the APIs should be executed
by the application only after it has received its notification that the APIs are
available.
In the HelloWorld2 application, this notification is accomplished through the
addition of an onload event defined in the page’s body section, as shown here:
Within the onBodyLoad function, the code registers an event listener that instructs
the application to call the onDeviceReady function when the device is ready, when
the PhoneGap application container has finished its initialization routines:
document.addEventListener("deviceready", onDeviceReady, false);
In this example application, the onDeviceReady function simply displays a
PhoneGap alert dialog (which is different from a JavaScript alert dialog), letting
the user know everything is OK:
navigator.notification.alert("PhoneGap is ready!")
In production applications, this function could update the user interface (UI) with
content created through API calls or do whatever other processing is required by
the application. You’ll see an example of this in the next sample application.
The PhoneGap Navigator
Many of the APIs implemented by PhoneGap are instantiated from the Navigator object.
Unfortunately, it’s not consistent; some do and some do not. Be sure to check the API
documentation before calling an API.
Leveraging PhoneGap APIs
Now that we know how to configure an application to wait until the PhoneGap
APIs are available, let’s build an application that actually uses the PhoneGap APIs
as shown in the following HelloWorld3 application.