Insetting the Ticker Into the page
Remember, that this decision was being made in 1999 when only IE supported the
IFRAME tag and all other browsers ignored it. Yes, we did expect that other browsers
might implement it in the future and now that future has arrived, we will review this later on in
the chapter, when we develop a new ticker for contemporary browsers. For now, we are looking at
the live deployed ticker.
IFRAME tag was assembled in such a way as to call in the ticker HTML
document only on IE. The other browsers would ignore the
IFRAME tag and see the HTML contained within it. This fragment of HTML is taken from the News Online front page:
<IFRAME SRC='/ticker/ticker.stm' WIDTH='315' HEIGHT='30' SCROLLING='no' FRAMEBORDER='0'> <APPLET CODE='ticker.class' CODEBASE='/java/' WIDTH='300' HEIGHT='50'> <PARAM NAME='bgcolor' VALUE='255,255,255'></PARAM> <PARAM NAME='linkcolor' VALUE='255,0,0'></PARAM> <PARAM NAME='textcolor' VALUE='0,0,0'></PARAM> <PARAM NAME='SectionID' VALUE='252'></PARAM> <PARAM NAME='LanguageID' VALUE='3'></PARAM> <PARAM NAME='RegionID' VALUE='-1'></PARAM> <PARAM NAME='SubRegionID' VALUE='-1'></PARAM> </APPLET> </IFRAME>
Conveniently, IE ignores the HTML between the
tags, while still implementing the
IFRAME. Netscape ignores the
IFRAME tags and
APPLET element inside. The applet parameters are not important to us here and are
provided to allow the tickers to be customized for different language variants of News Online.
So, the ticker runs within a frame that is placed at the top of the page (or wherever we like).
How It Works
The workings are fairly simple:
- Test that we are running in the correct browser
- Initialize any data structures
- Construct an interval timer that plays out the ticker text
- On each cycle, pick up a new headline and play it out
- After a pre-defined number of cycles, reload the ticker page
We will now take a closer look at these steps to consider the design choices and compromises that were made.
Created: November 5, 2001
Revised: November 5, 2001