The RSSReader constructor in Java

Print Quick Response Code in Java The RSSReader constructor

RSSReader = Class.create(); RSSReader.prototype = { initialize: function( readerId, options ) { this.id = readerId; this.transitionTimer = null; Set default this.paused = false; values this.visibleLayer = 0; this.setOptions(options); Set configuration options

this.start(); }, ... };

The constructor takes two arguments: an ID and an options object. The ID is used as a unique identifier for the reader and is used as a prefix for the IDs of the buttons that it will need to identify from the DOM. This will be shown shortly in the applyButtonBehaviors method. The first thing the constructor does b is to set the default values for its state. Next, the options object, as with most of the components we ve written, is used c to specify configuration options to the

component. This is done via the setOptions method. Finally, everything that needs to happen to bring the component to life happens in the start method d. Let s ponder configuration first, and then we ll move on to behavior. Our boilerplate configuration idiom, setOptions, shown in listing 13.28, provides the configuration. Let s establish the setOptions implementation now and talk about our configuration options.

setOptions: function(options) { this.options = { slideTransitionDelay: 7000, fadeDuration : 300, errorHTML : '<hr/>Error retrieving content.<br/>' }.extend(options); },

The properties we ve decided to make configurable in our RSS reader are indicated within the setOptions method shown here. The slideTransitionDelay property specifies the number of milliseconds an article s slide is visible before transitioning to the next one. The fadeDuration property specifies the amount of time in milliseconds it takes to fade out and subsequently fade in the next slide. Finally, if an error occurs while loading an RSS feed, the errorHTML property specifies the HTML to display as an error message. The defaults for these values, if not explicitly overridden by the user, are shown in this code. It s worth noting here that the component will expect an rssFeeds property of the options object to be passed in as the initial set of feeds to peruse. Because we can t really assume a reasonable default for this value, it s not defaulted within the setOptions method. The intent is that a reader will be created with an options object similar to the example shown here:

var options = { rssFeeds: [ "http://radio.javaranch.com/news/rss.xml", "http://radio.javaranch.com/pascarello/rss.xml", "http://radio.javaranch.com/bear/rss.xml", "http://radio.javaranch.com/lasse/rss.xml" ] }; var rssReader = new RSSReader('rssReader', options );

With creation and configuration quickly coded, it s time to peek behind the curtain at the magical start method that kicks everything off. We ll look at it briefly and cover its implications in the relevant sections that follow. Let s start by illustrating the implementation shown in listing 13.29.

start: function() { this.applyButtonBehaviors(); new Effect.FadeTo( this.getLayer(1), 0.0, 1, 1, {} ); this.loadRSSFeed(0,true); this.startSlideShow(false); },

The applyButtonBehaviors method sets up the onclick handlers for the previous, pause, next, and Add Feed buttons. This is the next method we ll discuss. The fade effect on the second line fades out the visible div element so that when the first slide is loaded it can be faded in. Note that in this implementation, we re using an effect provided by Rico rather than writing our own, which reduces the amount of code we have to write, debug, and maintain. The loadRSSFeed method initiates the Ajax request to load in the first feed, and the startSlideShow method starts a timer with the value of the slideTransitionDelay to initiate the slideshow. The loadRSSFeed method will be explored in more detail in the Loading RSS feeds with Ajax section (page 556), and the startSlideShow method will be dissected in the Slideshow functionality (page 549) section. As promised, we ll close our discussion of construction and setup by looking at the applyButtonBehaviors method in listing 13.29. The applyButtonBehaviors method, as mentioned previously, hooks the buttons up to methods that implement their behaviors. The implementation is shown in listing 13.30.