ios - 根据设备方向快速更改约束

Question

当设备从纵向旋转到横向时， View 的宽度约束会更新，但当设备从横向旋转到纵向时它不会更新

我的代码:

override func viewDidLoad() {
    super.viewDidLoad()
    theView.translatesAutoresizingMaskIntoConstraints = false
    theView.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
    theView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: 0).isActive = true
    theView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 0).isActive = true
    theView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: 0).isActive = true
  }

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {

当设备第一次从纵向旋转到横向时，“theView”宽度获得 View 宽度的 50%

    if UIDevice.current.orientation.isLandscape {  
       theView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.50).isActive = true

从横向旋转到纵向不会恢复原来的宽度

    } else {
       theView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1.00).isActive = true
    }   
}

这是一张显示我正在尝试做的事情的图片。

Answer 1

旋转时应该禁用右 anchor 约束。

因为 NSLayoutAnchor 类的 constraint 方法总是返回新的、不活动的约束，你应该保留对你想要激活/停用.

初始化可能看起来像这样。

override func viewDidLoad() {
    super.viewDidLoad()
    // ...        
    widthConstraint = theView.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 0.50)
    rightConstraint = theView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: 0)
    rightConstraint.isActive = true
}

有了这些引用，您就可以像这样实现您的 willRotate: 方法。

override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {
    if UIDevice.current.orientation.isLandscape {
        rightConstraint.isActive = false
        widthConstraint.isActive = true
    }
    else {
        rightConstraint.isActive = true
        widthConstraint.isActive = false
    }
}

它应该是这样的。