Tableview header position

I am using a table开发者_如何学运维View grouped style and after set headers for each group, its text is superposed to first cell. How to position group down in order to see header's text on top and previous to cell group? Thank you.

If you've implemented the tableView:viewForHeaderInSection: method to create header views, try to also implement the tableView:heightForHeaderInSection: method. Both are part of the UITableViewDelegate protocol