使用函数停用 viewdidload 中声明的 nslayoutconstraint

Question

我下面的代码在 viewdidload 中声明了布局约束。当调用函数 Selena 时，我希望将约束更改为函数 selena 中的内容。当我调用函数时，我不会更改对象。它没有效果。我知道我必须以某种方式停用原始约束。

   override func viewDidLoad() {

    NSLayoutConstraint.activate ([
        i.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
        i.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -200),

        i.widthAnchor.constraint(equalToConstant: 300),
        i.heightAnchor.constraint(equalToConstant: 450),

    ])

}


@objc func selena(){
    NSLayoutConstraint.activate ([
        i.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :50),
        i.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -50),

        i.widthAnchor.constraint(equalToConstant: 20),
        i.heightAnchor.constraint(equalToConstant: 450),

    ])

}

Answer 1

您需要将约束分配给变量，并在需要更改它们时更改其常量。这是带有尾随约束的示例。无需更改锚点，只需更改常量即可。这就是你的做法。

var iTrailingConstraint:NSLayoutConstraint?

override func viewDidLoad() {
   iTrailingConstraint = i.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150).isActive = true
}

调用 selena 时，您将常量设置为所需的动画。在控制器视图上调用 layoutIfNeeded()

@objc func selena(){
  UIView.animate(withDuration: 0.5, animations: {
    self.iTrailingConstraint?.constant = 50
    self.view.layoutIfNeeded()
  })
}

Answer 2

您可以引用它们然后使用 deactivate

  var oldCons = [NSLayoutConstraint]()

   override func viewDidLoad() {
       super.viewDidLoad()
     oldCons = [
        i.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :150),
        i.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -200), 
        i.widthAnchor.constraint(equalToConstant: 300),
        i.heightAnchor.constraint(equalToConstant: 450)
     ]
    NSLayoutConstraint.activate(oldCons)

}


@objc func selena(){

    NSLayoutConstraint.deactivate(oldCons)
    NSLayoutConstraint.activate ([
        i.trailingAnchor.constraint(equalTo: view.centerXAnchor, constant :50),
        i.topAnchor.constraint(equalTo: view.centerYAnchor, constant : -50), 
        i.widthAnchor.constraint(equalToConstant: 20),
        i.heightAnchor.constraint(equalToConstant: 450) 
    ])


}

height connstraint没有改变你可以从viewDidLoad

里面的数组中取出来

 i.heightAnchor.constraint(equalToConstant: 450).isActive = true

并将其从 selena 函数中删除

使用函数停用 viewdidload 中声明的 nslayoutconstraint

deactivate nslayoutconstraint declared in viewdidload with function

function

viewdidload

nslayoutconstraint

swift