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.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Evernote 6.13.2 - Create searchable note...
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
calibre 3.14.0 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
HoudahSpot 4.3.4 - Advanced file-search...
HoudahSpot is a versatile desktop search tool. Use HoudahSpot to locate hard-to-find files and keep frequently used files within reach. HoudahSpot will immediately feel familiar. It works just the... Read more
Hopper Disassembler 4.3.10- - Binary dis...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more
Hopper Disassembler 4.3.10- - Binary dis...
Hopper Disassembler is a binary disassembler, decompiler, and debugger for 32- and 64-bit executables. It will let you disassemble any binary you want, and provide you all the information about its... Read more
Paparazzi! 1.0b7 - Make user-defined siz...
Paparazzi! is a small utility for OS X that makes screenshots of webpages. This very simple tool takes screenshots of websites which do not fit on one screen. You specify the desired width, minimal... Read more
Amadeus Pro 2.4.4 - Multitrack sound rec...
Amadeus Pro lets you use your Mac for any audio-related task, such as live audio recording, digitizing tapes and records, converting between a variety of sound formats, etc. Thanks to its outstanding... Read more
Google Chrome 63.0.3239.108 - Modern and...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
Apple Configurator 2.6 - Configure and d...
Apple Configurator makes it easy to deploy iPad, iPhone, iPod touch, and Apple TV devices in your school or business. Use Apple Configurator to quickly configure large numbers of devices connected to... Read more
WhatRoute 2.0.26 - Geographically trace...
WhatRoute is designed to find the names of all the routers an IP packet passes through on its way from your Mac to a destination host. It also measures the round-trip time from your Mac to the router... Read more

Latest Forum Discussions

See All

WWE Mayhem guide - beginner tips and tri...
WWE Mayhem brings all of the familiar faces from your favorite wrestling league to mobile in this exciting new fighting game. Build up a team of your favorite WWE superstars and fight your way to the championship title, or battle against your... | Read more »
The best new games we played this week -...
We've made it through another week, so let's treat ourselves to some of the best new games to launch in the past few days. It was another exciting week with some long-awaited indie games making their debut, and some big console titles making the... | Read more »
Match blocks to pull off dance moves in...
Ferdinand: Unstoppabull is a brand new match three puzzler based on the animated movie of (almost) the same name. As you can expect, you have to match blocks together to complete a bunch of puzzling levels and earn a high score. [Read more] | Read more »
Lineage 2: Revolution’s end of year upda...
Now available in 54 countries worldwide, Lineage 2: Revolution is continuing its global quest to be the most popular mobile MMORPG by launching a jam-packed end of year update. Complete with many subtle tweaks to help improve users’ online... | Read more »
The 5 best Star Wars games on iOS
The time has almost come.Star Wars: The Last Jedifinally hits theaters in the cinematic event that might be bigger than Christmas. To celebrate, we're taking a look at the best--and only the best--Star Warsmobile games to date. [Read more] | Read more »
Life Is Strange (Games)
Life Is Strange 1.1 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1 (iTunes) Description: Life Is Strange is a five part episodic game that sets out to revolutionize story-based choice and consequence games by... | Read more »
Oddworld: New 'n' Tasty (Game...
Oddworld: New 'n' Tasty 1.0 Device: iOS Universal Category: Games Price: $7.99, Version: 1.0 (iTunes) Description: ** PLEASE NOTE: Requires 3.6GB free space to install. Runs at variable resolutions based on device capabilities.... | Read more »
Gorogoa (Games)
Gorogoa 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Gorogoa is an elegant evolution of the puzzle genre, told through a beautifully hand-drawn story designed and illustrated by Jason... | Read more »
Why Guns of Boom will be big for mobile...
Earlier this week, Game Insight, the minds that brought you Guns of Boom, revealed plans for an esports mode in the popular FPS title, with big implications for the game's future. Guns of Boom has been quite popular for some time now, so it's... | Read more »
The best mobile games to play on lazy ho...
With the holidays in full swing, there's hopefully going to be a lot of time off work lazing around the house. With all of that free time, it's a perfect opportunity to catch up on some mobile games that you might have missed out on earlier this... | Read more »

Price Scanner via MacPrices.net

Sunday flash sale: Beats Solo3 Wireless On-Ea...
Amazon has Beats Solo3 Wireless On-Ear Headphones on sale for $199.99 including free shipping. Their price is $100 off MSRP, and it’s the lowest price available for Beats Solo3. Multiple colors are... Read more
B&H Holiday sale: MacBooks for up to $300...
B&H Photo has Apple MacBook Pros, MacBook Airs, and 12″ MacBooks on sale for up to $300 off MSRP as part of their Holiday sale. B&H charges sales tax in NY & NJ only, and overnight... Read more
The lowest prices on Apple 13″ MacBook Pros t...
Save $300-$300 on the purchase of a 2017 13″ MacBook Pro this weekend with Certified Refurbished models at Apple. In many cases, Apple’s refurbished prices are the lowest available for each model... Read more
Lowest prices of the Holiday season: 15″ Appl...
Save $360-$420 on the purchase of a 2017 15″ MacBook Pro with Certified Refurbished models at Apple. In many cases, Apple’s refurbished prices are the lowest available for each model from any... Read more
Apple discounts Beats products by up to 30% t...
Apple has Beats by Dr. Dre (BeatsX, Powerbeats3 Wireless, and Beats Solo3 Wireless) on sale for up to 30% off their retail price from now until December 26th: – BeatsX: Was $149.95, now $99 –... Read more
Updated Price Trackers: Macs, iPads, iPhones,...
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: – 15″... Read more
How to preorder a new iMac Pro and pay zero s...
B&H Photo and Adorama are accepting preorders on multiple configurations of the new Apple iMac Pro. Both resellers charge sales tax for residents of NY & NJ only, and shipping is free.... Read more
Apple Macs back in stock at Amazon with model...
Amazon has MacBook Pros, MacBook Airs, MacBooks, and iMacs on sale for up to $200 off MSRP as part of their Holiday/Christmas sale. Shipping is free. Note that stock of some Macs may come and go (and... Read more
Apple offering free overnight delivery on all...
Apple is now offering free overnight delivery on all in stock products until 3pm local time on December 22nd. This includes new as well as refurbished computers. Click here for more information. Read more
Beats Holiday sale at B&H, headphones and...
B&H Photo has Beats by Dr. Dre headphones, earphones, and speakers on sale for up to $80 off MSRP as part of their Holiday sale. Expedited shipping is free, and B&H charges sales tax to NY... Read more

Jobs Board

*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform 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.