title: How to set an UIActivityIndicatorView when loading a UITableViewCell
body: <p>I have two <code>UITableViewController</code>s, A and B. When I tap one cell in table A, I will use <code>UINavigationController</code> to push table view controller B. But the data of B is downloaded from Internet, which takes several seconds. So I want to add a <code>UIActivityIndicatorView</code> when loading B. How can I achieve this?</p>