如何在使用constraintEqualToAnchor（）设置它们后更改自动布局约束？

我尝试使用constraintEqualToAnchor()设置具有AutoLayout约束的视图：

 override func viewDidLoad() { super.viewDidLoad() let myView = UIView() myView.backgroundColor = UIColor.orangeColor() myView.translatesAutoresizingMaskIntoConstraints = false view.addSubview(myView) myView.leftAnchor.constraintEqualToAnchor(view.leftAnchor).active = true myView.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor).active = true myView.topAnchor.constraintEqualToAnchor(view.topAnchor).active = true myView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor).active = true /******************************************/ /* I try to change one of the constraints */ /******************************************/ myView.leftAnchor.constraintEqualToAnchor(view.rightAnchor, constant: -100).active = true } 

在最后一行代码中，我尝试更改其中一个约束。 我认为它会工作，但它在控制台日志中给出了一些错误

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使用constraintEqualToAnchor()? ，在我设置它们后，改变约束的正确方法是什么？

Answer 1

您需要在激活新约束时停用先前的约束，这样您才不会过度约束视图。 为此，将每个约束的引用存储为ViewController的属性，然后在创建和激活新约束之前将旧约束的active属性设置为false ：

Swift 2.x：

 class ViewController: UIViewController { var leftConstraint: NSLayoutConstraint? var trailingConstraint: NSLayoutConstraint? var topConstraint: NSLayoutConstraint? var bottomConstraint: NSLayoutConstraint? override func viewDidLoad() { super.viewDidLoad() let myView = UIView() myView.backgroundColor = UIColor.orangeColor() myView.translatesAutoresizingMaskIntoConstraints = false view.addSubview(myView) leftConstraint = myView.leftAnchor.constraintEqualToAnchor(view.leftAnchor) leftConstraint?.active = true trailingConstraint = myView.trailingAnchor.constraintEqualToAnchor(view.trailingAnchor) trailingConstraint?.active = true topConstraint = myView.topAnchor.constraintEqualToAnchor(view.topAnchor) topConstraint?.active = true bottomConstraint = myView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor) bottomConstraint?.active = true /******************************************/ /* I try to change one of the constraints */ /******************************************/ leftConstraint?.active = false leftConstraint = myView.leftAnchor.constraintEqualToAnchor(view.rightAnchor, constant: -100) leftConstraint?.active = true } } 

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更新Swift 3语法：

 class ViewController: UIViewController { var leftConstraint: NSLayoutConstraint? var trailingConstraint: NSLayoutConstraint? var topConstraint: NSLayoutConstraint? var bottomConstraint: NSLayoutConstraint? override func viewDidLoad() { super.viewDidLoad() let myView = UIView() myView.backgroundColor = UIColor.orange myView.translatesAutoresizingMaskIntoConstraints = false view.addSubview(myView) leftConstraint = myView.leftAnchor.constraint(equalTo: view.leftAnchor) leftConstraint?.isActive = true trailingConstraint = myView.trailingAnchor.constraint(equalTo: view.trailingAnchor) trailingConstraint?.isActive = true topConstraint = myView.topAnchor.constraint(equalTo: view.topAnchor) topConstraint?.isActive = true bottomConstraint = myView.bottomAnchor.constraint(equalTo: view.bottomAnchor) bottomConstraint?.isActive = true /******************************************/ /* I try to change one of the constraints */ /******************************************/ leftConstraint?.isActive = false leftConstraint = myView.leftAnchor.constraint(equalTo: view.rightAnchor, constant: -100) leftConstraint?.isActive = true } } 

Answer 2

这是一个声明约束c的示例，该约束将在稍后的时间引用。 我们设置一个新的常量值，然后在superview上调用layout 。

 myView.translatesAutoresizingMaskIntoConstraints = false var constraints: [NSLayoutConstraint] = [ myView.topAnchor.constraintEqualToAnchor(view.topAnchor), myView.leftAnchor.constraintEqualToAnchor(view.leftAnchor), myView.bottomAnchor.constraintEqualToAnchor(view.bottomAnchor) ] let c = myView.rightAnchor.constraintEqualToAnchor(view.rightAnchor) constraints.append(c) view.addSubview(myView) NSLayoutConstraint.activateConstraints(constraints) // Some time later c.constant = -100 view.setNeedsLayout() 

Answer 3

 // method myView.topAnchor.constraintEqualToAnchor creates new one inactive anchor // and not returns exist with equal relationships // you can set identifier for any constraint in Interface Builder or code and find & update in code for ( NSLayoutConstraint *c in [self.view constraintsAffectingLayoutForAxis:UILayoutConstraintAxisHorizontal] ) { if ( YES == [c.identifier isEqualToString:@"my.layout-constraint.id"] ) { // Unlike the other properties, the constant can be modified // after constraint creation. // Setting the constant on an existing constraint performs much better // than removing the constraint and adding a new one that's exactly like // the old except that it has a different constant. c.constant = 123; // if needed // [self.view setNeedsUpdateConstraints]; break; } } 

Answer 4

以下是IF语句在单击分段时修改StackView和View的示例：

 if (sender as AnyObject).selectedSegmentIndex == 0{ // Shrink the white view and stack view heightConstraintView = containerView.heightAnchor.constraint(equalToConstant: 100) heightConstraintView?.isActive = true heightConstraintStackView = stackView.heightAnchor.constraint(equalToConstant: 100) heightConstraintStackView?.isActive = true } else { // Before returning back the white view and stack view DEACTIVATE teh previous constraints heightConstraintView?.isActive = false heightConstraintStackView?.isActive = false // Returning back the white view and stack view to normal size heightConstraintView = containerView.heightAnchor.constraint(equalToConstant: 200) heightConstraintView?.isActive = true heightConstraintStackView = stackView.heightAnchor.constraint(equalToConstant: 200) heightConstraintStackView?.isActive = true }