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

Latest Forum Discussions

See All

Top Mobile Game Discounts
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links... | Read more »
Price of Glory unleashes its 1.4 Alpha u...
As much as we all probably dislike Maths as a subject, we do have to hand it to geometry for giving us the good old Hexgrid, home of some of the best strategy games. One such example, Price of Glory, has dropped its 1.4 Alpha update, stocked full... | Read more »
The SLC 2025 kicks off this month to cro...
Ever since the Solo Leveling: Arise Championship 2025 was announced, I have been looking forward to it. The promotional clip they released a month or two back showed crowds going absolutely nuts for the previous competitions, so imagine the... | Read more »
Dive into some early Magicpunk fun as Cr...
Excellent news for fans of steampunk and magic; the Precursor Test for Magicpunk MMORPG Crystal of Atlan opens today. This rather fancy way of saying beta test will remain open until March 5th and is available for PC - boo - and Android devices -... | Read more »
Prepare to get your mind melted as Evang...
If you are a fan of sci-fi shooters and incredibly weird, mind-bending anime series, then you are in for a treat, as Goddess of Victory: Nikke is gearing up for its second collaboration with Evangelion. We were also treated to an upcoming... | Read more »
Square Enix gives with one hand and slap...
We have something of a mixed bag coming over from Square Enix HQ today. Two of their mobile games are revelling in life with new events keeping them alive, whilst another has been thrown onto the ever-growing discard pile Square is building. I... | Read more »
Let the world burn as you have some fest...
It is time to leave the world burning once again as you take a much-needed break from that whole “hero” lark and enjoy some celebrations in Genshin Impact. Version 5.4, Moonlight Amidst Dreams, will see you in Inazuma to attend the Mikawa Flower... | Read more »
Full Moon Over the Abyssal Sea lands on...
Aether Gazer has announced its latest major update, and it is one of the loveliest event names I have ever heard. Full Moon Over the Abyssal Sea is an amazing name, and it comes loaded with two side stories, a new S-grade Modifier, and some fancy... | Read more »
Open your own eatery for all the forest...
Very important question; when you read the title Zoo Restaurant, do you also immediately think of running a restaurant in which you cook Zoo animals as the course? I will just assume yes. Anyway, come June 23rd we will all be able to start up our... | Read more »
Crystal of Atlan opens registration for...
Nuverse was prominently featured in the last month for all the wrong reasons with the USA TikTok debacle, but now it is putting all that behind it and preparing for the Crystal of Atlan beta test. Taking place between February 18th and March 5th,... | Read more »

Price Scanner via MacPrices.net

AT&T is offering a 65% discount on the ne...
AT&T is offering the new iPhone 16e for up to 65% off their monthly finance fee with 36-months of service. No trade-in is required. Discount is applied via monthly bill credits over the 36 month... Read more
Use this code to get a free iPhone 13 at Visi...
For a limited time, use code SWEETDEAL to get a free 128GB iPhone 13 Visible, Verizon’s low-cost wireless cell service, Visible. Deal is valid when you purchase the Visible+ annual plan. Free... Read more
M4 Mac minis on sale for $50-$80 off MSRP at...
B&H Photo has M4 Mac minis in stock and on sale right now for $50 to $80 off Apple’s MSRP, each including free 1-2 day shipping to most US addresses: – M4 Mac mini (16GB/256GB): $549, $50 off... Read more
Buy an iPhone 16 at Boost Mobile and get one...
Boost Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering one year of free Unlimited service with the purchase of any iPhone 16. Purchase the iPhone at standard MSRP, and then choose... Read more
Get an iPhone 15 for only $299 at Boost Mobil...
Boost Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering the 128GB iPhone 15 for $299.99 including service with their Unlimited Premium plan (50GB of premium data, $60/month), or $20... Read more
Unreal Mobile is offering $100 off any new iP...
Unreal Mobile, an MVNO using AT&T and T-Mobile’s networks, is offering a $100 discount on any new iPhone with service. This includes new iPhone 16 models as well as iPhone 15, 14, 13, and SE... Read more
Apple drops prices on clearance iPhone 14 mod...
With today’s introduction of the new iPhone 16e, Apple has discontinued the iPhone 14, 14 Pro, and SE. In response, Apple has dropped prices on unlocked, Certified Refurbished, iPhone 14 models to a... Read more
B&H has 16-inch M4 Max MacBook Pros on sa...
B&H Photo is offering a $360-$410 discount on new 16-inch MacBook Pros with M4 Max CPUs right now. B&H offers free 1-2 day shipping to most US addresses: – 16″ M4 Max MacBook Pro (36GB/1TB/... Read more
Amazon is offering a $100 discount on the M4...
Amazon has the M4 Pro Mac mini discounted $100 off MSRP right now. Shipping is free. Their price is the lowest currently available for this popular mini: – Mac mini M4 Pro (24GB/512GB): $1299, $100... Read more
B&H continues to offer $150-$220 discount...
B&H Photo has 14-inch M4 MacBook Pros on sale for $150-$220 off MSRP. B&H offers free 1-2 day shipping to most US addresses: – 14″ M4 MacBook Pro (16GB/512GB): $1449, $150 off MSRP – 14″ M4... Read more

Jobs Board

All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.