//默认选中第一行
NSIndexPath *firstPath = [NSIndexPath indexPathForRow:0 inSection:0];
[self._tableView selectRowAtIndexPath:firstPath animated:YES scrollPosition:UITableViewScrollPositionTop];
//选中背景自定义
cell.selectedBackgroundView=[[[UIImageView alloc]initWithImage:[UIImage imageNamed:@"cell_selected_bg"]]autorelease];