title: How to detect when a custom tableview cell goes off the screen?
body: <p>In my app I have a custom tableViewCell,</p>
  
  <p>I also have a View Controller with a tableView, where I display custom tableViewCells.</p>
  
  <p>Is there a method (ViewController method or TableViewCell method) which fires when tableViewCell goes off the screen, I need to make some Core Data updates in it for my cell.</p>
  
  <p>(I need to know the method, because I need to update Core Data value of Timer() in my tableViewCell when it goes off the screen.)</p>