Developing Offline Web Applications - HTML5 Programming for ASP.NET Developers - page 215

Table 8-2. Events of the applicationCache Object

Event Description

checking Raised when the browser detects a web page's manifest attribute.

downloading Raised when the browser begins downloading files listed in an application's cache

manifest file.

progress

Raised periodically during the download process.

cached Raised when an application has been downloaded successfully and cached on the local

machine.

updateready

Raised when the browser has successfully downloaded an updated version of a
previously cached application.

noupdate

Raised when the browser detects that no update is required for an already cached
application.

obsolete

Raised when the browser detects that the cache manifest of a previously cached
application is no longer available on the server.

error

Raised when there is an error during any of the other events.

To understand how you can use these events, let's wire some of them into the Clock application (see
Listing 8-11). The Clock application essentially uses these events to notify the end user about the
associated operations.

Listing 8-11. Using applicationCache Object Events
$(document).ready(function () {
...
$(applicationCache).bind("checking",NotifyUser);
$(applicationCache).bind("downloading", NotifyUser);
$(applicationCache).bind("progress", NotifyUser);
$(applicationCache).bind("cached", NotifyUser);
$(applicationCache).bind("updateready", NotifyUser);
$(applicationCache).bind("noupdate", NotifyUser);
$(applicationCache).bind("obsolete", NotifyUser);
$(applicationCache).bind("error", NotifyUser);
});

function NotifyUser(evt) {
alert(evt.type);
if (evt.type == 'updateready') {
if (confirm('An updated version of this application is available.' +
'Do you wish to use the new version now?'))
{
applicationCache.swapCache();
}
}
}

This code binds the applicationCache events listed in Table 8-1 to a common event handler function
NotifyUser() . The NotifyUser() function displays the event type ( checking , downloading , progress , and so
on). Notice the if block: if the event type is updateready , it means an updated version of the application is
available. In most cases, you want the user to use the updated version immediately. One way to