//为UIView绘制单边的boder
let TopBorder = CALayer()
TopBorder.frame = CGRect(x: 0.0, y:0, width: section3BottomView.frame.size.width, height: 1.0)
TopBorder.backgroundColor = UIColor.init(hexColor: COLOR_GRAY).cgColor
section3BottomView.layer.addSublayer(TopBorder)
OC版：
CALayer *TopBorder = [[CALayer alloc]init];
TopBorder.frame = CGRectMake(0, self.chatLabel.frame.size.height, self.chatLabel.frame.size.width, 0.5);
TopBorder.backgroundColor = [hlColor colorWithHexString:@"e0dfdf"].CGColor;
[self.chatLabel.layer addSublayer:TopBorder];
