Method viewForHeaderInSection delegate was not triggered

[eternalBlast]

-(UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{
    UIView *view = [UIView new];
    view.frame = CGRectMake(0, 0, 320, 30);
    [view setBackgroundColor:[UIColor grayColor]];
    return view;
}

self.tableView.sectionHeaderHeight = 20;
self.tableView.estimatedSectionHeaderHeight = 20;

The above method is not triggered even has set the sectionHeaderHeight and estimatedSectionHeaderHeight. Any approach to solve this problem? Please help. Thanks.