Swift - UILable背景图层圆角，Lable大小随文字自适应

        // 1.创建Lable var lbl:UILabel? = UILabel()
        lbl!.text = app!.name! + "正在下载……"
        lbl!.textAlignment = NSTextAlignment.Center;
        lbl!.textColor = UIColor.whiteColor()
        lbl!.font = UIFont.systemFontOfSize(13)

        

        // 2.通过Lable的文字获取自适应区域 var rect:CGRect = lbl!.text!.boundingRectWithSize(CGSize(width: 260.0 ,height: 10000.0), options: NSStringDrawingOptions.UsesLineFragmentOrigin, attributes: [NSFontAttributeName:lbl!.font], context: nil)
       
        // 3.设置Label的frame
 var marginBottom:CGFloat = 100

        // 3.1.根据刚才的所获取到自适应宽高加上适当值来设置lable的宽高 var width:CGFloat = rect.width + 48 var height:CGFloat = rect.height + 12 var x = (self.superview!.frame.width - width) / 2 var y = self.superview!.frame.height - marginBottom
        lbl!.frame = CGRect(x: x, y: y, width: width, height: height)

        

        // 4设置lable背景圆角
        // 4.1.设置圆角图层背景颜色
        lbl!.layer.backgroundColor = UIColor.blackColor().CGColor // 4.2.设置圆角值 
        lbl!.layer.cornerRadius = 5
 
 //该处应该用lbl.clip^方法。切掉超出layer的的区域
　　　　 lbl!clipsToBounds = true
 self.superview?.addSubview(lbl!)

     
        // 5.实现动画移除控件 UIView .animateWithDuration(5, animations: { () -> Void in

            lbl!.alpha = 0.7
            lbl!.alpha = 0
            }) { (Bool) -> Void in
                lbl!.removeFromSuperview()
                lbl = nil
        }