更改UITableView.tableHeadView的高度

CGFloat changeHeight = 20;
CGRect newFrame = headView.frame;
newFrame.size.height = newFrame.size.height + changeHeight;
headView.frame = newFrame;
[self.tableView setTableHeaderView:headView];
//增加动画效果
[self.tableView beginUpdates];
[self.tableView setTableHeaderView:headView];
[self.tableView endUpdates];