TweetFollow Us on Twitter

Creating a Dashboard Widget that Processes an RSS Feed

Volume Number: 24 (2008)
Issue Number: 07
Column Tag: Dashboard Widget

Creating a Dashboard Widget that Processes an RSS Feed

What is an RSS feed and how do I process it from within a Dashboard Widget?

by Mihalis Tsoukalos

Article Overview

A Dashboard Widget, named "GetRSS'' Widget, that uses the RSS technology, is going to be programmed in this article using JavaScript, CSS and HTML code as well as some PNG image files. The "GetRSS'' Widget uses the XMLHttpRequest object from the JavaScript programming language to get data from the MacTech RSS feed and present it in a Dashboard Widget fashion.

Because of the unknown amount of the incoming RSS data, this Widget needs to include a scroll bar–a forthcoming article is going to fully present the scroll bar technique. For the purposes of this article, only RSS-related material is going to be explained.

Also, the presented Widget has a backside! Combining two or more techniques is relatively simple as long as you already know how to use each one of them in isolation.

What is RSS?

RSS (Really Simple Syndication) is a Web content syndication format. RSS is a dialect of XML (Extensible Markup Language) and all RSS files must conform to the XML 1.0 specification. It is extensively used by news websites, weblogs and podcasting. The RSS protocol transfers information in an XML file format that is called RSS feed, RSS stream, webfeed or RSS channel.

Two most important advantages of RSS are that the RSS information is transferred as plain text, and that you can use a news aggregator to automatically get the updated information.

A news aggregator is a category of software that can get RSS feed information and present it to the user. Aggregators trim down the time and effort required for frequently checking the websites you want for updates. Using an aggregator you can subscribe to an RSS feed that it will check for new content at user-determined intervals, and retrieve the new content without further human intervention.

The following is a small part of RSS code, taken from MacTech's News RSS: (http://www.mactech.com/news/mactech.rss):

<?xml version="1.0" encoding="UTF-8"?>
<!— generator="wordpress/1.5" —>
<rss version="2.0" 
   xmlns:content="http://purl.org/rss/1.0/modules/content/"
   xmlns:wfw="http://wellformedweb.org/CommentAPI/"
   xmlns:dc="http://purl.org/dc/elements/1.1/"
>
<channel>
   <title>MacTech News</title>
<!—
   [[link]][[?php bloginfo_rss('url') ?]][[/link]]
—>
   <link>http://www.mactech.com/</link>
   <description>MacTech News is the source of news, information, updates and special offers specifically for the Mac technical community.</description>
   <pubDate>Fri, 14 Mar 2008 14:30:31 -0800</pubDate>
   <generator>http://wordpress.org/?v=1.5</generator>
   <language>en</language>
      <item>
      <title>OWC Announces Mercury Elite-AL Pro Firewire+USB2 1TB Drives</title>
      <link>http://www.mactech.com/news/?p=1010258</link>
      <comments>http://www.mactech.com/news/?p=1010258#comments</comments>
      <pubDate>Fri, 14 Mar 2008 06:30:31 -0800</pubDate>
      <dc:creator>Administrator</dc:creator>
      
   <category>Breaking News</category>
      <guid>http://www.mactech.com/news/?p=1010258</guid>
      <description><![CDATA[OWC ANNOUNCES NEW MERCURY ELITE-AL PRO FIREWIRE+USB2 1 TB STORAGE DRIVES
=46ast, Economical FireWire+USB 2.0 Combo External Drive Solutions Feature
New Oxford 934 Chipset and the Latest SATA Technology
Woodstock, IL, March 14, [...]]]></description>
      <wfw:commentRSS>http://www.mactech.com/news/wp-commentsrss2.php?p=1010258</wfw:commentRSS>
   </item>
      <item>
      <title>New Take Control Ebook Helps Switch from PC to Mac</title>
      <link>http://www.mactech.com/news/?p=1010257</link>
      <comments>http://www.mactech.com/news/?p=1010257#comments</comments>

The listing above will help you understand the RSS feed format. The first line dictates that you are using XML version 1.0 with UTF-8 Unicode character encoding. The second and third line tells that you are using RSS version 2.0 code that is created using the WordPress semantic personal publishing software (line 2). The other lines tell you where you can find the definitions of the various standards. You can also find out that each entry (or record) is included inside the <item> tag and consists of the following tags: <title>, <link>, <comments>, <pubDate>, <dc:creator>, <category>, <guid>, <description> and <wfw:commentRSS>. You will later have to decide which of the information you want to include inside your Widget's output.

Which files compose the complete GetRSS Widget?

The files that compose the GetRSS Widget are the following:

1. Info.plist: a file necessary for every Widget.

2. GetRSS.html: the main HTML file for the "GetRSS" Widget.

3. GetRSS.js: the JavaScript code needed for the "GetRSS" Widget.

4. GetRSS.css: the CSS file needed for formatting the Widget.

5. Two image files called Default.png and Icon.png. Every Dashboard Widget has these two graphics files. The Icon.png file should be 82x82 pixels and is displayed in the Dashboard Widget Bar.

6. Some other files and directories that will be shown later on.

The Info.plist file

The contents of the Info.plist file are the following:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
    "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>AllowNetworkAccess</key>
    <true/>
    <key>BackwardsCompatibleClassLookup</key>
    <true/>
    <key>CFBundleIdentifier</key>
    <string>com.mtsouk.widget.getrss</string>
    <key>CFBundleName</key>
    <string>GetRSS</string>
    <key>CFBundleShortVersionString</key>
    <string>2.0</string>
    <key>CFBundleVersion</key>
    <string>200</string>
    <key>CloseBoxInsetX</key>
    <integer>8</integer>
    <key>CloseBoxInsetY</key>
    <integer>7</integer>
    <key>MainHTML</key>
    <string>GetRSS.html</string>
</dict>
</plist>

The GetRSS.html file

The contents of the GetRSS.html can be found in the archive for this article at ftp.mactech.com/src/mactech/volume24_2008/24.07.sit. It should be noted that the GetRSS.html file acts as the glue that connects all the other Widget files. It is also easy to understand that the GetRSS.html file contains uncomplicated HTML code. Most of its code is typical and is included in every Widget that uses certain Dashboard features.

The GetRSS.css File

The contents of the GetRSS.css file can be found in the source archive for this column found at ftp.mactech.com/src/mactech/volume24_2008/24.07.sit. The CSS code may look big and complex, but this is not the case. Most of the CSS code is standard for widgets, and is repeated in every widget that has a backside and a scroll bar.

The GetRSS.js File

The GetRSS.js file is the most important file of the whole Widget. A small mistake in it and the Widget will either misbehave or not work at all. Its contents are also in the archive for this article. Later in, "Explaining the Technique," will further explain the technique and you will better understand the JavaScript code.

Before continuing with the rest of the article, I will have to tell you a little problem that I had with this particular Widget. I first wrote this Widget using Mac OS X 10.4 and it worked fine. When I got the Mac OS X 10.5 DVD and first tried the Widget, it did not work as expected. When I pressed on a link, the link was not working. The following JavaScript code (the output of the diff UNIX utility) shows a small modification that I made for the Widget to work:

<       widget.openURL (div.the_link);
<    } else document.location = div.the_link;
—-
>       widget.openURL(div.getAttribute('the_link'));
>    } 
>    else
>       document.location = div.getAttribute('the_link');

It turns out that the div.the_link code was not working as expected in Leopard. I had to use div.getAttribute('the_link') instead for the Widget to work. In Tiger, those notations were, more or less, equivalent.

The full list of the "GetRSS" Widget files

The following is the full list of the files that compose the "GetRSS" Widget.

drwxr-xr-x   AppleClasses
-rw-r—r—   Default.png
-rw-r—r—   GetRSS.css
-rw-r—r—   GetRSS.html
-rw-r—r—   GetRSS.js
-rw-r—r—   Icon.png
drwxr-xr-x   Images
-rw-r—r—   Info.plist
./AppleClasses:
AppleAnimator.js
AppleButton.js
AppleInfoButton.js
AppleScrollArea.js
AppleScrollbar.js
Images/
./AppleClasses/Images:
scroll_thumb_hleft.png
scroll_thumb_hmid.png
scroll_thumb_hright.png
scroll_thumb_vbottom.png
scroll_thumb_vmid.png
scroll_thumb_vtop.png
scroll_track_hleft.png
scroll_track_hmid.png
scroll_track_hright.png
scroll_track_vbottom.png
scroll_track_vmid.png
scroll_track_vtop.png
slide_thumb.png
slide_track_hleft.png
slide_track_hmid.png
slide_track_hright.png
slide_track_vbottom.png
slide_track_vmid.png
slide_track_vtop.png
./Images:
BackSide.png
background.png
dark.png
light.png
top.png
well.png

NOTE: You can find the JavaScript files contained in the AppleClasses directory of the Widget inside the /System/Library/WidgetResources/AppleClasses/ directory. You will also find the ./AppleClasses/Images directory along with its contents there.

Figure 1 shows the image files that can be found inside the ./Images directory of the Widget.


Figure 1: The images of the ./Images directory

The files found inside the AppleClasses/Images directory of the Widget are provided by Apple and can be found in /Developer/Applications/Dashcode.app/Contents/Resources/AppleClasses/Images/ on a Leopard system–provided that you have Dashcode installed.

Explaining the technique

The most challenging part of this Widget is the GetRSS.js JavaScript file. The following function, called load() does the necessary initializations of the JavaScript objects.

function load()
{
    scrollbar = new
    AppleVerticalScrollbar(document.getElementById("myScrollBar"));
    scrollArea = new
    AppleScrollArea(document.getElementById("contents"), scrollbar);
    scrollArea.scrollsHorizontally = false;
    scrollArea.singlepressScrollPixels = 15;
whiteInfoButton = new AppleInfoButton(document.getElementById("flipper"),
    document.getElementById("front"), "white", "white", showBack);
glassButton = new AppleGlassButton(document.getElementById("doneButton"),
"Done", showFront);
    window.onfocus = function () { scrollArea.focus(); }
    window.onblur = function () { scrollArea.blur(); }
    if (!window.widget)
    {
        show();
    }
}

An attention-grabbing JavaScript function is the show() function which is defined as follows:

function show ()
{
    var now = (new Date).getTime();
    
    // only check if 15 minutes have passed
    if ((now - last_updated) > 900000)
    {
        if (xml_request != null)
        {
            xml_request.abort();
            xml_request = null;
        }
        xml_request = new XMLHttpRequest();
        xml_request.onload = function(e) {xml_loaded(e, xml_request);}
        xml_request.overrideMimeType("text/xml");
        xml_request.open("GET", feed.url);
        xml_request.setRequestHeader("Cache-Control", "no-cache");
        xml_request.send(null);
    }
}

The 900000 time value–it represents the minimum refresh time value–is in milliseconds and is therefore equivalent to 15 minutes (900000/1000 = 900 seconds. 900 / 60 = 15 minutes). Then, a new XMLHttpRequest() object is defined. This object holds the RSS feed data after is processed by the xml_loaded(e, request) function. The xml_loaded(e, request) function extracts the data from the required RSS feed fields using the following JavaScript code:

for( var item = channel.firstChild; item != null; item = item.nextSibling)
{
    if( item.nodeName == 'item' )
    {
        var title = findChild (item, 'title');
        // we have to have the title to include the item in the list
        if( title != null )
        {
            var link = findChild (item, 'link');
            var pubDate = findChild (item, 'pubDate');
            results[results.length] = {title:title.firstChild.data,
                link:(link != null ? link.firstChild.data : null),
                date:new Date(Date.parse(pubDate.firstChild.data))
           };
        }
    }
}

The above JavaScript code parses the RSS feed and mines the wanted information. It only looks for the <item>, <title>, <link> and <pubDate> tags and their respective data.


Figure 2: The "GetRSS" Widget look


Figure 3: The backside of the Widget

It is also both interesting and educational to look at the clickOnTitle(event, div) function definition that introduces the widget.openURL() function.

function clickOnTitle(event, div)
{
   if (window.widget)
   {
      widget.openURL(div.getAttribute('the_link'));
   } 
   else
      document.location = div.getAttribute('the_link');
}

The widget.openURL() method opens the given URL in the (default) web browser which resides outside Dashboard.

Inside the JavaScript code you saw some alert() function calls which are the best technique for debugging Widgets. alert() output is written to the Console. Please remember to remove your alert() function calls when you finish debugging or otherwise your Console logs may become too crowded.

Conclusions

Using a Widget to read RSS feeds is a very valuable technique, especially now that Widgets are getting more and more popular. It is also an efficient way of keeping a close eye on an RSS feed without having to open a dedicated browser window. Finally, please note: The RSS-related code of this article is heavily based on the "Sample RSS" Widget code that is provided by Apple in the "/Developer/Examples/Dashboard/Sample RSS" directory of a Tiger system. Strangely enough, Leopard does not have the "/Developer/Examples/Dashboard" directory with the Widget examples. Also note that the "Sample RSS" Widget does not have a backside.

Bibliography and References

1. RSS: http://www.rssboard.org

2. RSS 2.0.1 specification: http://www.rssboard.org/rss-2-0-1

3. XML 1.0: http://www.w3.org/TR/REC-xml

4. WordPress software: http://wordpress.org

5. The XMLHttpRequest object: http://www.w3.org/TR/XMLHttpRequest

6. XMLHttpRequest object: http://developer.apple.com/internet/webcontent/xmlhttpreq.html

7. Ben Hammersley, Developing Feeds with RSS and Atom, O'Reilly & Associates, 2005

8. Leslie M. Orchard, Hacking RSS and Atom. John Wiley & Sons, 2005

9. Elliote Rusty Harold and W. Scott Means, XML in a nutshell, O'Reilly & Associates, 2002


Mihalis Tsoukalos lives in Greece with his wife Eugenia and enjoys digital photography and writing articles. He is the author of the "Programming Dashboard Widgets" eBook. You can reach him at tsoukalos@sch.gr.

 
AAPL
$102.64
Apple Inc.
+1.58
MSFT
$46.56
Microsoft Corpora
-0.50
GOOG
$581.13
Google Inc.
-6.24

MacTech Search:
Community Search:

Software Updates via MacUpdate

GarageSale 6.8 - Create outstanding eBay...
GarageSale is a slick, full-featured client application for the eBay online auction system. Create and manage your auctions with ease. With GarageSale, you can create, edit, track, and manage... Read more
ScreenFlow 4.5.3 - Create screen recordi...
Save 5% with the MacUpdate coupon code: 68031AE15F -- Buy now! ScreenFlow is powerful, easy-to-use screencasting software for the Mac. With ScreenFlow you can record the contents of your entire... Read more
NeoOffice 2014.3 - Mac-tailored, OpenOff...
NeoOffice is a complete office suite for OS X. With NeoOffice, users can view, edit, and save OpenOffice documents, PDF files, and most Microsoft Word, Excel, and PowerPoint documents. NeoOffice 3.x... Read more
Typinator 6.2 - Speedy and reliable text...
Typinator turbo-charges your typing productivity. Type a little. Typinator does the rest. We've all faced projects that require repetitive typing tasks. With Typinator, you can store commonly used... Read more
PopChar X 6.7 - Floating window shows av...
PopChar X helps you get the most out of your font collection. With its crystal-clear interface, PopChar X provides a frustration-free way to access any font's special characters. Expanded... Read more
Evernote 5.6.0 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
Monosnap 2.2.2 - Versatile screenshot ut...
Monosnap allows you to save screenshots easily, conveniently, and quickly, sharing them with friends and colleagues at once. It's the ideal choice for anyone who is looking for a smart and fast... Read more
Tunnelblick 3.4beta36 - GUI for OpenVPN...
Tunnelblick is a free, open source graphic user interface for OpenVPN on OS X. It provides easy control of OpenVPN client and/or server connections. It comes as a ready-to-use application with all... Read more
SoftRAID 5.0.4 - High-quality RAID manag...
SoftRAID allows you to create and manage disk arrays to increase performance and reliability. SoftRAID's intuitive interface and powerful feature set makes this utility a must have for any Mac OS X... Read more
Audio Hijack Pro 2.11.3 - Record and enh...
Audio Hijack Pro drastically changes the way you use audio on your computer, giving you the freedom to listen to audio when you want and how you want. Record and enhance any audio with Audio Hijack... Read more

Latest Forum Discussions

See All

Manual – Custom exposure camera (Photog...
Manual – Custom exposure camera 1.0 Device: iOS iPhone Category: Photography Price: $1.99, Version: 1.0 (iTunes) Description: Custom exposure for your iPhone camera. A powerful camera app with full control over your image. Quickly... | Read more »
Why I Don’t Want to Upgrade to the iPhon...
I’ve been living with my iPhone 4S for the past two years or so, and if I was living in a world where I wasn’t bombarded with new phone announcements and people of the general public caring enough to upgrade constantly, I wouldn’t think my phone... | Read more »
Tictail Review
Tictail Review By Jennifer Allen on September 23rd, 2014 Our Rating: :: CLASSY SHOPPINGiPhone App - Designed for the iPhone, compatible with the iPad Tictail is an attractive and stylish way of looking for some great new clothes... | Read more »
Super Glyph Quest is Bringing More Match...
Super Glyph Quest is Bringing More Match-3 Magics to the App Store Soon Posted by Jessica Fisher on September 23rd, 2014 [ permalink ] Fans of Glyph Quest, by Alex Trowers and Leanne Bayley, | Read more »
Sword King Review
Sword King Review By Jennifer Allen on September 23rd, 2014 Our Rating: :: WEAK, SO WEAKUniversal App - Designed for iPhone and iPad Ever wanted to tap on a screen and assume you’ve killed a monster or two? Probably not, but just... | Read more »
Pangea Software Unveil Bundles and iOS 8...
Pangea Software Unveil Bundles and iOS 8 Updates Posted by Ellis Spice on September 23rd, 2014 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Race Team Manager Review
Race Team Manager Review By Jennifer Allen on September 23rd, 2014 Our Rating: :: LIGHT RACINGUniversal App - Designed for iPhone and iPad Want to be in charge of a racing team but not be overwhelmed by tactics and options? Race... | Read more »
Kobojo Works with Creative Minds from Fi...
Kobojo has announced details for their newest game, Zodiac – a 2D persistent online RPG. Kobojo has put together a crack team of developers including composer Hitoshi Sakimoto and scenario writer Kazushige Nojima, whose work includes many of the... | Read more »
PlayHaus Review
PlayHaus Review By Amy Solomon on September 23rd, 2014 Our Rating: iPad Only App - Designed for the iPad PlayHaus is a interesting, stylish app for young children, full of cause-and-effect interactions.   | Read more »
Astropolo Review
Astropolo Review By Amy Solomon on September 23rd, 2014 Our Rating: Universal App - Designed for iPhone and iPad Astropolo is a space-themed children’s app with a great sense of style.   | Read more »

Price Scanner via MacPrices.net

Razer DeathAdder Chroma Gaming Mouse Upgraded...
Razer has announced the launch of their new Razer DeathAdder Chroma gaming mouse. Even if you’re not a gamer, the DeathAdder bears considering. I’m a fan of the hard-wired tracking accuracy,... Read more
Check Apple prices on your device with iTracx
MacPrices is proud to offer readers a free iOS app (iPhones, iPads, & iPod touch) and Android app (Google Play and Amazon App Store) called iTracx, which allows you to glance at today’s lowest... Read more
Refurbished 2013 MacBook Pros available for u...
The Apple Store has Apple Certified Refurbished 13″ and 15″ MacBook Pros available starting at $929. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.5GHz MacBook Pros (4GB RAM/... Read more
New iPhones Score Big in SquareTrade Breakabi...
SquareTrade has announced the iPhone 6 and its larger sibling, iPhone 6 Plus, performed impressively in Breakability testing, and each carries the top Breakability Score in their respective category... Read more
10 Million + First Weekend Sales Set New iPho...
Apple has announced it sold over 10 million new iPhone 6 and iPhone 6 Plus models, a new record, just three days after the launch on September 19. iPhone 6 and iPhone 6 Plus are now available in the... Read more
Betty Crocker Launches New Cookbook for iOS
Betty Crocker, a General Mills brand, an established food industry leader, has announced its free digital cookbook app has been refreshed to make cooking with iPhone, iPad and iPod touch even easier... Read more
Apple restocks some refurbished 2014 MacBook...
The Apple Store has restocked some Apple Certified Refurbished 2014 MacBook Airs, with prices starting at $769. An Apple one-year warranty is included with each MacBook, and shipping is free. These... Read more
13-inch 128GB MacBook Air on sale for $949, s...
B&H Photo has the new 2014 13″ 1.4GHz/128GB MacBook Air on sale for $949.99 including free shipping plus NY tax only. Their price is $50 off MSRP. B&H will also include free copies of... Read more
Apple offering free $25 iTunes Gift Card with...
The Apple Store is offering a free $25 iTunes Gift Card with the purchase of a $99 Apple TV for a limited time. Shipping is free. Read more
Apple refurbished iPod touch available for up...
The Apple Store has Apple Certified Refurbished 5th generation iPod touches available starting at $149. Apple’s one-year warranty is included with each model, and shipping is free. Most colors are... Read more

Jobs Board

*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Senior Event Manager, *Apple* Retail Market...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global event strategy. Delivering an overarching brand story; in-store, Read more
*Apple* Solutions Consultant (ASC) - Apple (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Project Manager / Business Analyst, WW *Appl...
…a senior project manager / business analyst to work within our Worldwide Apple Fulfillment Operations and the Business Process Re-engineering team. This role will work Read more
*Apple* Retail - Multiple Positions (US) - A...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.