iOS 用代码添加约束
contentView.translatesAutoresizingMaskIntoConstraints = false
let attributes: [NSLayoutConstraint.Attribute] = [.leading, .trailing, .top, .bottom]
let constraints = attributes.map({
NSLayoutConstraint(
item: contentView,
attribute: $0,
relatedBy: .equal,
toItem: view,
attribute: $0,
multiplier: 1,
constant: 0)
})
view.addConstraints(constraints)
