func setViewConstraints() {
//系统默认会给autoresizing 约束,要关闭autoresizing才能让自定义的约束生效,否则程序崩溃
customView.translatesAutoresizingMaskIntoConstraints = false
//添加约束:"哪个控件" 的 “什么属性“ "等于/大于/小于" “另一个控件” 的 “什么属性” 乘以 "多少" 加上 "多少"
let Constraint_centerX = NSLayoutConstraint(item: customView, attribute: .centerX, relatedBy: .equal, toItem: otherView, attribute: .centerX, multiplier: 1, constant: 0)
let Constraint_centerY = NSLayoutConstraint(item: customView, attribute: .centerY, relatedBy: .equal, toItem: otherView, attribute: .centerY, multiplier: 1, constant: 0)
let Constraint_width = NSLayoutConstraint(item: customView, attribute: .width, relatedBy: .lessThanOrEqual, toItem: otherView, attribute: .width, multiplier: 1, constant: 20)
let Constraint_height = NSLayoutConstraint(item: customView, attribute: .height, relatedBy: .lessThanOrEqual, toItem: otherView, attribute: .height, multiplier: 1, constant: 20)
//激活约束
NSLayoutConstraint.activate([Constraint_centerX,Constraint_centerY,Constraint_width,Constraint_height])
}