UITableView的indexPathForCell:返回总是0作为indexPath.row

I have a UITableView with custom cells in it. This custom cell looks like a normal cell with Style "Detail Left". But my custom cell has a detail label and a text field, to allow the user to edit the text. I have a Save button where I want to save all data the user entered. I made up the custom cell using this tutorial: I have a UITableView with custom cells in it. T