我尝试重新分配推荐nslayoutconstraint。
class ViewController: UIViewController {
@IBOutlet weak var myConstraint: NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
exchangeConstraint(&myConstraint)
}
}
extension UIViewController {
func exchangeConstraint(_ constraint: inout NSLayoutConstraint) {
let spacing = constraint.constant
view.removeConstraint(constraint)
constraint = view.topAnchor.constraint(equalTo: anotherView.topAnchor, constant: spacing)
view.addConstraint(constraint)
}
}
,但这里给我带来了错误:
exchangeConstraint(&myConstraint)
-------------------^
Cannot pass immutable value of type 'NSLayoutConstraint' as inout argument
我不明白的是为什么它说不变的价值,而约束被声明为变量,而不是常数。
我通过简单地将constraint
参数声明为明确的无包裹的NSLayoutConstraint
。
func exchangeConstraint(_ constraint: inout NSLayoutConstraint!) {
...
}
update
这是一个我使用的项目:https://github.com/truffls/compatible-layout-anchors-anchors-ios