为了更好地解释，我编写了以下内容。这演示了两种修复子视图布局的方法。使用约束时，我更喜欢将约束创建为数组，并在一次激活它们，正如您将在createredSquareWithConstraints的代码中看到的那样。约束只是一个线性方程，将一个视图的特征与另一个视图的特征相关联。例如，在“伪代码”中，我的数组中的第一个约束可以写成：
“将子视图的前导边距设置为容器视图的前导边距的1倍加上常数0。”
（这就是为什么我之前感到困惑的原因，因为在我看来，您正在根据其子视图的特征设置包含视图的约束。）
虽然使用布局约束仍然完全有效，但我认为现在首选的方法是覆盖viewWillTransitionToSize（）委托方法，该方法仅要求您指定给定包含视图大小的情况下，视图控制器的子视图的框架应该是什么。因此，我也包括了这种实现，创建了一个具有初始框架的黄色正方形，每当调用viewWillTransitionToSize时就会修改该框架。我个人发现这比使用布局约束要简单得多。
如果您尝试按下按钮并旋转屏幕，您会发现两种方法都可以实现同样的效果。[注意：我将一个正方形标记为受限制的，另一个标记为不受限制的，但实际上它们当然都是受限制的，只是以不同的方式。我想补充说明的是，这显然不是您在实践中应该采取的做法 - 您应该选择一种方法并坚持使用，否则您的代码将无处不在！]
希望这有所帮助！
import UIKit
class ViewController: UIViewController {
var constrainedredSquare : UIView!
var unconstrainedRedSquare : UIView!
var methodOneButton : UIButton!
var methodTwoButton : UIButton!
override func viewDidLoad() {
super.viewDidLoad()
self.view.backgroundColor = UIColor.blue
func getButton(name: String) -> UIButton {
let button : UIButton = UIButton()
button.backgroundColor = UIColor.white
button.layer.cornerRadius = 3
button.clipsToBounds = true
button.setTitle(name, for: UIControlState.normal)
button.setTitleColor(UIColor.black, for: UIControlState.normal)
return button
}
self.methodOneButton = getButton(name: "Red - Constraints")
self.methodTwoButton = getButton(name: "Yellow - viewWillTransitionToSize")
self.methodOneButton.addTarget(self, action: #selector(self.createRedSquareWithConstraints), for: .touchUpInside)
self.methodTwoButton.addTarget(self, action: #selector(self.createYellowSquareWithoutConstraints), for: .touchUpInside)
self.methodOneButton.frame = CGRect(origin: CGPoint(x: 200, y: 100), size: CGSize(width: 300, height: 300))
self.methodTwoButton.frame = CGRect(origin: CGPoint(x: self.view.frame.width - 500, y: 100), size: CGSize(width: 300, height: 300))
self.view.addSubview(self.methodOneButton)
self.view.addSubview(self.methodTwoButton)
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
}
override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
if let _ = self.unconstrainedRedSquare {
self.unconstrainedRedSquare.frame = CGRect(origin: CGPoint.zero, size: size)
}
self.methodOneButton.frame = CGRect(origin: CGPoint(x: 200, y: 100), size: CGSize(width: 300, height: 300))
self.methodTwoButton.frame = CGRect(origin: CGPoint(x: size.width - 500, y: 100), size: CGSize(width: 300, height: 300))
}
func createYellowSquareWithoutConstraints() {
if let _ = self.unconstrainedRedSquare {
self.unconstrainedRedSquare.removeFromSuperview()
}
else
{
if let _ = constrainedredSquare {
self.constrainedredSquare.removeFromSuperview()
}
self.unconstrainedRedSquare = UIView()
self.unconstrainedRedSquare.backgroundColor = UIColor.yellow
self.unconstrainedRedSquare.frame = CGRect(origin: CGPoint.zero, size: self.view.frame.size)
self.view.addSubview(self.unconstrainedRedSquare)
self.view.bringSubview(toFront: self.methodOneButton)
self.view.bringSubview(toFront: self.methodTwoButton)
}
}
func createRedSquareWithConstraints() {
if let _ = self.constrainedredSquare {
self.constrainedredSquare.removeFromSuperview()
}
else
{
if let _ = self.unconstrainedRedSquare {
self.unconstrainedRedSquare.removeFromSuperview()
}
let redSquare : UIView = UIView()
redSquare.backgroundColor = UIColor.red
self.view.addSubview(redSquare)
self.view.bringSubview(toFront: self.methodOneButton)
self.view.bringSubview(toFront: self.methodTwoButton)
let rsConstraints : [NSLayoutConstraint] = [NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.leading, multiplier: 1.0, constant: 0),
NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.trailing, multiplier: 1.0, constant: 0),
NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.top, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.top, multiplier: 1.0, constant: 0),
NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.bottom, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.bottom, multiplier: 1.0, constant: 0),
NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.width, multiplier: 1.0, constant: 0),
NSLayoutConstraint(item: redSquare, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.height, multiplier: 1.0, constant: 0)]
redSquare.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate(rsConstraints)
}
}
}
