禁用视图中声明的带有函数的declared约束

Question

下面的代码在视图加载中声明了布局约束。当函数selena被调用时，我希望约束更改为Selena函数中的约束。当我调用函数时，我不会更改对象。它没有效果。我知道，不知怎么的，我必须解除原来的约束。

   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

您可以保存对它们的引用，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) 
    ])


}

高度连接没有改变，您可以将其从viewDidLoad中的数组中提取出来

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

并将其从selena函数中删除

Answer 2

您需要将约束赋值给变量，并在需要更改它们时更改它们的常量。下面是带有尾部约束的示例。没有必要改变锚，只有常数。你就是这样做的。

var iTrailingConstraint:NSLayoutConstraint?

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

调用selena时，可以将常量动画到所需的常量。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()
  })
}