title: iPhone achieve smooth animation using progress bar timer
body: <p>I am trying to implement a simple quiz app on the iphone in the spirit of learning, part of this app is a timer.</p>
  
  <p>I want my timer to count down from 10 to 0.  I had a simple NSTimer that repeats and calls a method every second and in this method I update a label which displays the remaining time, which works nicely.</p>
  
  <p>Now instead of displaying the timer using a label I wanted to use a graphical progress bar, so I created ten images, one full in length (representing 10), the next 9/10 of the size and so on, and in my repeating timer method instead of updating a label I update a UIImage with the appropriate image so over time the progress bar gets smaller and smaller.  </p>
  
  <p>My problem is that due to the way I have implemented the progress bar, it doesn't look very smooth when it updates every second.  Is there another way I should approach developing this kind of functionality?  I have heard that you could use a stretchable image to get a smoother effect but I couldn't see any good examples of that.  </p>
  
  <p>Any advice and code samples welcome, just trying to learn here.</p>