纯代码布局控件

private func setUI() {
addSubview(iconView)//添加控件
for view in subviews {//遍历所用控件并设置可以使用addConstrain布局，如果没有这句代码则下面的布局代码无效。
view.translatesAutoresizingMaskIntoConstraints = false
}
//约束布局
//iconView
addConstraint(NSLayoutConstraint(item: iconView, attribute: .centerX, relatedBy: .equal, toItem: self, attribute: .centerX, multiplier: 1.0, constant: 0))
addConstraint(NSLayoutConstraint(item: iconView, attribute: .centerY, relatedBy: .equal, toItem: self, attribute: .centerY, multiplier: 1.0, constant: -80))
}