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

Check out the new Pirate Attack update i...
Love pirates and board games? Well, you'll love the new Pirate Attack themed update that just launched in Game of Dice. It adds a bunch of new content themed around pirates, like an all new event map based on a pirate ship which revamps the toll... | Read more »
Splash Cars guide - How to paint the tow...
Splash Cars is an arcade driving game that feels like a hybrid between Dawn of the Plow and Splatoon. In it, you'll need to drive a car around to repaint areas of a town that have lost all of their color. Check out these tips to help you perform... | Read more »
The best video player on mobile
We all know the stock video player on iOS is not particularly convenient, primarily because it asks us to hook a device up to iTunes to sync video in a world that has things like Netflix. [Read more] | Read more »
Four apps to help improve your Super Bow...
Super Bowl Sunday is upon us, and whether you’re a Panthers or a Broncos fan you’re no doubt gearing up for it. [Read more] | Read more »
LooperSonic (Music)
LooperSonic 1.0 Device: iOS Universal Category: Music Price: $4.99, Version: 1.0 (iTunes) Description: LooperSonic is a multi-track audio looper and recorder that will take your loops to the next level. Use it like a loop pedal to... | Read more »
Space Grunts guide - How to survive
Space Grunts is a fast-paced roguelike from popular iOS developer, Orange Pixel. While it taps into many of the typical roguelike sensibilities, you might still find yourself caught out by a few things. We delved further to find you some helpful... | Read more »
Dreii guide - How to play well with othe...
Dreii is a rather stylish and wonderful puzzle game that’s reminiscent of cooperative games like Journey. If that sounds immensely appealing, then you should immediately get cracking and give it a whirl. We can offer you some tips and tricks on... | Read more »
Kill the Plumber World guide - How to ou...
You already know how to hop around like Mario, but do you know how to defeat him? Those are your marching orders in Kill the Plumber, and it's not always as easy as it looks. Here are some tips to get you started. This is not a seasoned platform... | Read more »
Planar Conquest (Games)
Planar Conquest 1.0 Device: iOS Universal Category: Games Price: $12.99, Version: 1.0 (iTunes) Description: IMPORTANT: Planar Conquest is compatible only with iPad 3 & newer devices, iPhone 5 & newer. It’s NOT compatible with... | Read more »
We talk to Cheetah Mobile about its plan...
Piano Tiles 2 is a fast-paced rhythm action high score chaser out now on iOS and Android. You have to tap a series of black tiles that appear on the screen in time to the music, being careful not to accidentally hit anywhere else. Do that and it's... | Read more »

Price Scanner via MacPrices.net

12-inch 1.2GHz Silver Retina MacBook on sale...
B&H Photo has the 12″ 1.2GHz Silver Retina MacBook on sale for $1399 including free shipping plus NY sales tax only. Their price is $200 off MSRP, and it’s the lowest price for this model from... Read more
iPads on sale at Target: $100 off iPad Air 2,...
Target has WiFi iPad Air 2s and iPad mini 4s on sale for up to $100 off MSRP on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale prices for... Read more
Target offers Apple Watch for $100 off MSRP
Target has Apple Watches on sale for $100 for a limited time. Choose free shipping or free local store pickup (if available). Sale prices for online orders only, in-store prices may vary: - Apple... Read more
Apple refurbished 2014 13-inch Retina MacBook...
Apple has Certified Refurbished 2014 13″ Retina MacBook Pros available for up to $400 off original MSRP, starting at $979. An Apple one-year warranty is included with each model, and shipping is free... Read more
Macs available for up to $300 off MSRP, $20 o...
Purchase a new Mac or iPad using Apple’s Education Store and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free, and... Read more
Watch Super Bowl 50 Live On Your iPad For Fre...
Watch Super Bowl 50 LIVE on the CBS Sports app for iPad and Apple TV. Get the app and then tune in Sunday, February 7, 2016 at 6:30 PM ET to catch every moment of the big game. The CBS Sports app is... Read more
Two-thirds Of All Smart Watches Shipped In 20...
Apple dominated the smart watch market in 2015, accounting for over 12 million units and two-thirds of all shipments according to Canalys market research analysts’ estimates. Samsung returned to... Read more
12-inch 1.2GHz Retina MacBooks on sale for up...
B&H Photo has 12″ 1.2GHz Retina MacBooks on sale for $180 off MSRP. Shipping is free, and B&H charges NY tax only: - 12″ 1.2GHz Gray Retina MacBook: $1499 $100 off MSRP - 12″ 1.2GHz Silver... Read more
12-inch 1.1GHz Gray Retina MacBook on sale fo...
B&H Photo has the 12″ 1.1GHz Gray Retina MacBook on sale for $1199 including free shipping plus NY sales tax only. Their price is $100 off MSRP, and it’s the lowest price available for this model... Read more
Apple now offering full line of Certified Ref...
Apple now has a full line of Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models 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
*Apple* Subject Matter Expert - Experis (Uni...
This position is for an Apple Subject Matter Expert to assist in developing the architecture, support and services for integration of Apple devices into the domain. Read more
*Apple* Macintosh OSX - Net2Source Inc. (Uni...
…: * Work Authorization : * Contact Number(Best time to reach you) : Skills : Apple Macintosh OSX Location : New York, New York. Duartion : 6+ Months The associate would Read more
Computer Operations Technician ll - *Apple*...
# Web Announcement** Apple Technical Liaison**The George Mason University, Information Technology Services (ITS), Technology Support Services, Desktop Support Read more
Restaurant Manager - Apple Gilroy Inc./Apple...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.