title: (iphone) how to update only one row in tableview
body: <p>I hava a <code>tableview</code>,and I will updata the data in the <code>tableview</code>.it receive datas every one second,when the data is received,it will replace the old data in one row.
  I do like this:
  when the data is received,i call</p>
  
  <pre><code>[m_tableView reloadData];
  </code></pre>
  
  <p>so,it will call</p>
  
  <pre><code>-(UITableViewCell*)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath  *)indexPath{ }
  </code></pre>
  
  <p>so i will change the specific row data in this method,but how can i set the <code>row index</code>?</p>