title: iOS : WHO'S in charge of refreshing UI/Screen while UITableView's scrolling?
body: <p>I was finding ways to calculate FPS as <a href="https://stackoverflow.com/q/26888434/889538">what I said here</a>, holding the idea that when the UITableView scrolls, its <code>drawRect:</code> would be called frame by frame. But it didn't.</p>
  <p>The UITableView's <code>drawRect:</code> will be called only once, not matter I drag it up and down quickly or put buttons on it. So does the UITableView's superview and cells. All the UIViews' <code>drawRect:</code>s are called only once for each.</p>
  <p>Given that <code>drawRect:</code> called only once, WHO is in charge of refreshing UI/Screen while UITableView's scrolling?</p>
  <h1>UPDATED 1</h1>
  <blockquote>
  <p>I know UITableView's delegate &amp; dataSource are responsible for layout
  cells to show. But what if tableView just scrolls slightly? Though its
  delegate &amp; dataSource are not called, the screen's content still
  changed. On this occasion, who is up to the UI refresh on iPhone
  screen? scrollView scrolled -&gt; UIKit -&gt; GPU -&gt; LCD Screen?</p>
  </blockquote>