wmorein.com > iPhone > Refreshing Content

For a lot of simple informational apps, the ability to update the page or the data on the page is key. As part of playing around with the Seattle Traffic page I've been digging in to this topic a little. The key issues I'm trying to determine are the following:

• Does the concept of automatically updating pages make sense on the iPhone in the first place?
• What techniques work on the iPhone and what are their limitations?
• What unique properties of the iPhone dictate doing things in a different way?

Background Research:

• meta refresh: The classic meta refresh seems to work fine to refresh the entire page periodically.
• setInterval(): A general way to periodically run some JavaScript. Here is an example I use in the traffic page to update the image without refreshing the whole page:

     function imgReload()
     {
       img = document.getElementById('map');
       img.src = 'http://images.wsdot.wa.gov/nwflow/flowmaps/bridges.gif?' +
                 Math.random();
     }
  
     setInterval('imgReload()', 500000);
  

  This sets things to update every 5 min. The Math.random() piece is there to ensure that the diagram actually gets updated.
• JavaScript running time limitation: In the Apple design guidelines, they note that JavaScript execution is limited to 5 seconds. I was initially worried that meant that you couldn't fire off periodic refresh or other events, but that does not seem to be the case -- setInterval() works fine even if the interval is >5 seconds.
• App switching effect: The key limitation in this approach is that any time the browser switches from being the active app (which happens if you use the home button to go to any other app).
• Auto-Lock: If your iPhone Auto-Locks or if you manually lock it, when you wake it up *sometimes* it will automatically refresh the page. I haven't figured out the exact rules yet for why it only happens sometimes -- I'm guessing it might be time based.