title: UITableViewCell height based on available screen space
body: <p>I wanted to create a layout for my <code>UITableView</code> such that it's divided into 2 sections:
   the first section has 3 rows of standard height (44px), 
  and the second section has one row, which contains a <code>UITextView</code> which completely fills up this cell. The tricky part is that I want to size this <code>textView</code>'s cell row to the height of the visible <code>tableview</code> area, such that the text view takes up the remaining view on screen. How do I find out, within </p>
  
  <p><code>- (CGFloat)tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath</code> </p>
  
  <p>what the remaining height looks like? I had previously made hard-coded assumptions based on the two iPhone screen sizes available (480 and 568) but with the new iPhone6 and iPhone 6+ screen, I don't want to use any assumed values for calculating this.</p>