如何动态更改最后一个单元格的UITableViewCell大小

I have a UITableView with 16-20 cells inside with dynamic cell size. When a cell expands it self it should also move itself to the top of the screen. I did that using "UITableView setContentOffset" method. It works well except for the last cell in table, it's not able to move itself to the top.I have a UITableView with 16-20 cells inside wi