let labels = UILabel()
labels.backgroundColor = UIColor.blackColor()
labels.textColor = UIColor.whiteColor()
labels.layer.masksToBounds = true
labels.layer.cornerRadius = 5
labels.textAlignment = NSTextAlignment.Center
labels.alpha = 0.5
labels.text = "..."
super.view.addSubview(labels)
//自动布局
labels.translatesAutoresizingMaskIntoConstraints = false
//底部约束
let bottom:NSLayoutConstraint = NSLayoutConstraint(item: labels, attribute: NSLayoutAttribute.Bottom, relatedBy:NSLayoutRelation.Equal, toItem:self.view, attribute:NSLayoutAttribute.Bottom, multiplier:1.0, constant: -30)
labels.superview!.addConstraint(bottom)//父控件添加约束
//中心对齐
let center:NSLayoutConstraint = NSLayoutConstraint(item: labels, attribute: NSLayoutAttribute.CenterX, relatedBy:NSLayoutRelation.Equal, toItem:self.view, attribute:NSLayoutAttribute.CenterX, multiplier:1.0, constant: 0)
labels.superview!.addConstraint(center)//父控件添加约束
//宽度约束
let width:NSLayoutConstraint = NSLayoutConstraint(item: labels, attribute: NSLayoutAttribute.Width, relatedBy:NSLayoutRelation.Equal, toItem:nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier:0.0, constant:120)
labels.addConstraint(width)//自己添加约束
//高度约束
let height:NSLayoutConstraint = NSLayoutConstraint(item: labels, attribute: NSLayoutAttribute.Height, relatedBy:NSLayoutRelation.Equal, toItem:nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier:0.0, constant:30)
labels.addConstraint(height)//自己添加约束