title: How to keep UITableView contentoffset after calling -reloadData
body: <pre><code>CGPoint offset = [_table contentOffset];
  [_table reloadData];
  [_table setContentOffset:offset animated:NO];    //unuseful
  
  //    __block UITableView *tableBlock = _table;
  //    [self performBlock:^(id sender) {
  //        [tableBlock setContentOffset:offset];
  //    } afterDelay:2];
  </code></pre>
  
  <p>I know don't know of any delegate method which gets called after <code>reloadData</code>. 
  And using <code>afterDelay:2</code> which is kind of a hack may be too short or too long, so how can I implement it?</p>