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，视图的宽度约束会更新，但是当设备从横向旋转到纵向时，视图的宽度约束不会更新

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) {

首次将设备从纵向旋转为横向时，“ theView”宽度为视图宽度的50％

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

从横向旋转到纵向无法恢复原始宽度

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

这是一张图像，显示了我正在尝试做的事情。

Answer 1

旋转时，应禁用右锚约束。

因为类的constraintmethod NSLayoutAnchor总是返回新的非活动约束，所以您应保留对要激活/停用的约束的引用。

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，您可以willRotate:像这样实现您的方法。

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
    }
}

它应该看起来像这样。