根据内容更新UITableViewCell的编辑样式

I am creating a table-based interface similar to iPad Contacts, in which the user can add to a list of rows by tapping a blank row at the bottom. The table is always in editing mode, and non-blank rows should have a standard delete editing icon to the left. As soon as the user starts typing in the last blank row, a delete icon should be added to the left (and a new blank row added).I am creating a table-based interface similar t