title: UITableView got slowly when dragging
body: <p>I am new to iPhone development, and I can not understand the working principle of UITableView well.</p>
  
  <p>I customize the UITableViewCell, and the cell contains imageview. In addition, I initialize the cell reusable. However, when I drag the UITableView, it scrolls slowly.</p>
  
  <p>Then what should I do to process it?</p>