Swift | 以编程方式添加约束

自上周以来，我试图弄清楚这一点，而没有再进一步。 好的，所以我需要在Swift中以编程方式应用一些约束条件来使用这个代码：

 var new_view:UIView! = UIView(frame: CGRectMake(0, 0, 100, 100)); new_view.backgroundColor = UIColor.redColor(); view.addSubview(new_view); var constX:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0); self.view.addConstraint(constX); var constY:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: self.view, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0); self.view.addConstraint(constY); var constW:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: new_view, attribute: NSLayoutAttribute.Width, multiplier: 1, constant: 0); self.view.addConstraint(constW); var constH:NSLayoutConstraint = NSLayoutConstraint(item: new_view, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: new_view, attribute: NSLayoutAttribute.Height, multiplier: 1, constant: 0); self.view.addConstraint(constH); 

但Xcode返回这个奇怪的输出：

 2014-10-03 09:48:12.657 Test[35088:2454916] Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) ( "<NSLayoutConstraint:0x7fa4ea446830 UIView:0x7fa4ea429290.centerX == UIView:0x7fa4ea4470f0.centerX>", "<NSAutoresizingMaskLayoutConstraint:0x7fa4ea4516c0 h=--& v=--& UIView:0x7fa4ea429290.midX == + 50>", "<NSLayoutConstraint:0x7fa4ea452830 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7fa4ea4470f0(375)]>", "<NSAutoresizingMaskLayoutConstraint:0x7fa4ea446db0 h=-&- v=-&- 'UIView-Encapsulated-Layout-Left' H:|-(0)-[UIView:0x7fa4ea4470f0] (Names: '|':UIWindow:0x7fa4ea444b20 )>" ) Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7fa4ea446830 UIView:0x7fa4ea429290.centerX == UIView:0x7fa4ea4470f0.centerX> Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful. 2014-10-03 09:48:12.658 Test[35088:2454916] Unable to simultaneously satisfy constraints. Probably at least one of the constraints in the following list is one you don't want. Try this: (1) look at each constraint and try to figure out which you don't expect; (2) find the code that added the unwanted constraint or constraints and fix it. (Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) ( "<NSLayoutConstraint:0x7fa4ea44d160 UIView:0x7fa4ea429290.centerY == UIView:0x7fa4ea4470f0.centerY>", "<NSAutoresizingMaskLayoutConstraint:0x7fa4ea451b30 h=--& v=--& UIView:0x7fa4ea429290.midY == + 50>", "<NSLayoutConstraint:0x7fa4ea44cf00 'UIView-Encapsulated-Layout-Height' V:[UIView:0x7fa4ea4470f0(667)]>", "<NSAutoresizingMaskLayoutConstraint:0x7fa4ea452700 h=-&- v=-&- 'UIView-Encapsulated-Layout-Top' V:|-(0)-[UIView:0x7fa4ea4470f0] (Names: '|':UIWindow:0x7fa4ea444b20 )>" ) Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7fa4ea44d160 UIView:0x7fa4ea429290.centerY == UIView:0x7fa4ea4470f0.centerY> Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger. The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful. 

你可以帮我吗？ 非常感谢

Answer 1

你是否打算在UIViewController的UIView中有一个宽度为100 ， 高度为100的UIView ？ 如果是这样，你可以尝试以下6种自动布局风格之一（Swift 4 / iOS 11）：

---

1.使用NSLayoutConstraint初始值设定项

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let horizontalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0) let verticalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0) let widthConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100) let heightConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100) view.addConstraints([horizontalConstraint, verticalConstraint, widthConstraint, heightConstraint]) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let horizontalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0) let verticalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0) let widthConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100) let heightConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100) NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint, widthConstraint, heightConstraint]) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0).isActive = true NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0).isActive = true NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true } 

---

2.使用视觉格式语言

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let views = ["view": view!, "newView": newView] let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:[view]-(<=0)-[newView(100)]", options: NSLayoutFormatOptions.alignAllCenterY, metrics: nil, views: views) let verticalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:[view]-(<=0)-[newView(100)]", options: NSLayoutFormatOptions.alignAllCenterX, metrics: nil, views: views) view.addConstraints(horizontalConstraints) view.addConstraints(verticalConstraints) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let views = ["view": view!, "newView": newView] let horizontalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:[view]-(<=0)-[newView(100)]", options: NSLayoutFormatOptions.alignAllCenterY, metrics: nil, views: views) let verticalConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:[view]-(<=0)-[newView(100)]", options: NSLayoutFormatOptions.alignAllCenterX, metrics: nil, views: views) NSLayoutConstraint.activate(horizontalConstraints) NSLayoutConstraint.activate(verticalConstraints) } 

---

3.使用NSLayoutConstraint初始值设定项和Visual Format Language的组合

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let views = ["newView": newView] let widthConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:[newView(100)]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) let heightConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:[newView(100)]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) let horizontalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0) let verticalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0) view.addConstraints(widthConstraints) view.addConstraints(heightConstraints) view.addConstraints([horizontalConstraint, verticalConstraint]) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let views = ["newView": newView] let widthConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:[newView(100)]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) let heightConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:[newView(100)]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) let horizontalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0) let verticalConstraint = NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0) NSLayoutConstraint.activate(widthConstraints) NSLayoutConstraint.activate(heightConstraints) NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint]) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let views = ["newView": newView] let widthConstraints = NSLayoutConstraint.constraints(withVisualFormat: "H:[newView(100)]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) let heightConstraints = NSLayoutConstraint.constraints(withVisualFormat: "V:[newView(100)]", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: views) NSLayoutConstraint.activate(widthConstraints) NSLayoutConstraint.activate(heightConstraints) NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0).isActive = true NSLayoutConstraint(item: newView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0).isActive = true } 

---

4.使用UIViewAutoresizing

注意：在运行时，Spring和Struts将被转换成相应的自动布局约束。

 override func viewDidLoad() { let newView = UIView(frame: CGRect(x: 0, y: 0, width: 100, height: 100)) newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = true newView.center = CGPoint(x: view.bounds.midX, y: view.bounds.midY) newView.autoresizingMask = [UIViewAutoresizing.flexibleLeftMargin, UIViewAutoresizing.flexibleRightMargin, UIViewAutoresizing.flexibleTopMargin, UIViewAutoresizing.flexibleBottomMargin] } 

---

5.使用NSLayoutAnchor

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let horizontalConstraint = newView.centerXAnchor.constraint(equalTo: view.centerXAnchor) let verticalConstraint = newView.centerYAnchor.constraint(equalTo: view.centerYAnchor) let widthConstraint = newView.widthAnchor.constraint(equalToConstant: 100) let heightConstraint = newView.heightAnchor.constraint(equalToConstant: 100) view.addConstraints([horizontalConstraint, verticalConstraint, widthConstraint, heightConstraint]) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let horizontalConstraint = newView.centerXAnchor.constraint(equalTo: view.centerXAnchor) let verticalConstraint = newView.centerYAnchor.constraint(equalTo: view.centerYAnchor) let widthConstraint = newView.widthAnchor.constraint(equalToConstant: 100) let heightConstraint = newView.heightAnchor.constraint(equalToConstant: 100) NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint, widthConstraint, heightConstraint]) } 

 override func viewDidLoad() { let newView = UIView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false newView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true newView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true newView.widthAnchor.constraint(equalToConstant: 100).isActive = true newView.heightAnchor.constraint(equalToConstant: 100).isActive = true } 

---

6.使用intrinsicContentSize和NSLayoutAnchor

 import UIKit class CustomView: UIView { override var intrinsicContentSize: CGSize { return CGSize(width: 100, height: 100) } } class ViewController: UIViewController { override func viewDidLoad() { let newView = CustomView() newView.backgroundColor = UIColor.red view.addSubview(newView) newView.translatesAutoresizingMaskIntoConstraints = false let horizontalConstraint = newView.centerXAnchor.constraint(equalTo: view.centerXAnchor) let verticalConstraint = newView.centerYAnchor.constraint(equalTo: view.centerYAnchor) NSLayoutConstraint.activate([horizontalConstraint, verticalConstraint]) } } 

Answer 2

它帮助我学习视觉，所以这是一个补充答案。

样板代码

 override func viewDidLoad() { super.viewDidLoad() let myView = UIView() myView.backgroundColor = UIColor.blue myView.translatesAutoresizingMaskIntoConstraints = false view.addSubview(myView) // Add constraints code here // ... } 

以下每个例子都是独立的。

钉左边缘

myView.leading = leadingMargin + 20

方法1：锚定样式

 let margins = view.layoutMarginsGuide myView.leadingAnchor.constraint(equalTo: margins.leadingAnchor, constant: 20).isActive = true 

• 除了leadingAnchor ，还有topAnchor ， bottomAnchor和bottomAnchor 。

方法2：NSLayoutConstraint样式

 NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.leadingMargin, multiplier: 1.0, constant: 20.0).isActive = true 

• 除.leading之外，还有.trailing ， .bottom和.bottom 。
• 除了.leadingMargin ，还有.trailingMargin ， .topMargin和.bottomMargin 。

设置宽度和高度

width = 200
height = 100

方法1：锚定样式

 myView.widthAnchor.constraint(equalToConstant: 200).isActive = true myView.heightAnchor.constraint(equalToConstant: 100).isActive = true 

方法2：NSLayoutConstraint样式

 NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.width, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 200).isActive = true NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 100).isActive = true 

在容器中心

myView.centerX = centerX
myView.centerY = centerY

方法1：锚定样式

 myView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true myView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true 

方法2：NSLayoutConstraint样式

 NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0).isActive = true NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0).isActive = true 

笔记

• 锚样式是NSLayoutConstraint样式的首选方法，但它只能从iOS 9，所以如果你是支持iOS 8，那么你仍然应该使用NSLayoutConstraint样式。
• 上面的例子显示了正在关注的一个或两个限制。 但是，为了在我的testing项目中正确放置myView ，我需要有四个约束。

进一步阅读

• 以编程方式创build约束文档

Answer 3

如果你想填补你的超级观点，那么我build议更快捷的方式：

  view.translatesAutoresizingMaskIntoConstraints = false let attributes: [NSLayoutAttribute] = [.top, .bottom, .right, .left] NSLayoutConstraint.activate(attributes.map { NSLayoutConstraint(item: view, attribute: $0, relatedBy: .equal, toItem: view.superview, attribute: $0, multiplier: 1, constant: 0) }) 

其他方面，如果你需要非平等的约束检查从iOS 9的NSLayoutAnchor。它往往更容易阅读，直接使用NSLayoutConstraint：

  view.translatesAutoresizingMaskIntoConstraints = false view.topAnchor.constraint(equalTo: view.superview!.topAnchor).isActive = true view.bottomAnchor.constraint(equalTo: view.superview!.bottomAnchor).isActive = true view.leadingAnchor.constraint(equalTo: view.superview!.leadingAnchor, constant: 10).isActive = true view.trailingAnchor.constraint(equalTo: view.superview!.trailingAnchor, constant: 10).isActive = true 

Answer 4

如错误消息所示，问题是您有与显式约束冲突的NSAutoresizingMaskLayoutConstraintstypes的约束，因为new_view.translatesAutoresizingMaskIntoConstraints设置为true。

这是您在代码中创build的视图的默认设置。 你可以像这样closures它：

 var new_view:UIView! = UIView(frame: CGRectMake(0, 0, 100, 100)) new_view.translatesAutoresizingMaskIntoConstraints = false 

另外，你的宽度和高度的限制是奇怪的。 如果你希望视图具有恒定的宽度，这是正确的方法：

 new_view.addConstraint(NSLayoutConstraint( item:new_view, attribute:NSLayoutAttribute.Width, relatedBy:NSLayoutRelation.Equal, toItem:nil, attribute:NSLayoutAttribute.NotAnAttribute, multiplier:0, constant:100)) 

（用你想要的宽度replace100。）

如果您的部署目标是iOS 9.0或更高版本，则可以使用此较短的代码：

 new_view.widthAnchor.constraintEqualToConstant(100).active = true 

无论如何，对于这样的布局（固定大小和父视图居中），使用自动识别掩码会更简单，并让系统将掩码转换为约束：

 var new_view:UIView! = UIView(frame: CGRectMake(0, 0, 100, 100)) new_view.backgroundColor = UIColor.redColor(); view.addSubview(new_view); // This is the default setting but be explicit anyway... new_view.translatesAutoresizingMaskIntoConstraints = true new_view.autoresizingMask = [ .FlexibleTopMargin, .FlexibleBottomMargin, .FlexibleLeftMargin, .FlexibleRightMargin ] new_view.center = CGPointMake(view.bounds.midX, view.bounds.midY) 

请注意，使用自动调整是完全合法的，即使你也使用自动布局。 （UIKit在内部的很多地方仍然使用自动resize）。问题是，对使用自动调整的视图应用附加约束很困难。

Answer 5

更新了Swift 3

 import UIKit class ViewController: UIViewController { let redView: UIView = { let view = UIView() view.translatesAutoresizingMaskIntoConstraints = false view.backgroundColor = .red return view }() override func viewDidLoad() { super.viewDidLoad() setupViews() setupAutoLayout() } func setupViews() { view.backgroundColor = .white view.addSubview(redView) } func setupAutoLayout() { // Available from iOS 9 commonly known as Anchoring System for AutoLayout... redView.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 20).isActive = true redView.rightAnchor.constraint(equalTo: view.rightAnchor, constant: -20).isActive = true redView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true redView.heightAnchor.constraint(equalToConstant: 300).isActive = true // You can also modified above last two lines as follows by commenting above & uncommenting below lines... // redView.topAnchor.constraint(equalTo: view.topAnchor, constant: 20).isActive = true // redView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true } } 

约束types

  /* // regular use 1.leftAnchor 2.rightAnchor 3.topAnchor // intermediate use 4.widthAnchor 5.heightAnchor 6.bottomAnchor 7.centerXAnchor 8.centerYAnchor // rare use 9.leadingAnchor 10.trailingAnchor etc. (note: very project to project) */ 

Answer 6

  var xCenterConstraint : NSLayoutConstraint! var yCenterConstraint: NSLayoutConstraint! xCenterConstraint = NSLayoutConstraint(item: self.view, attribute: .CenterX, relatedBy: .Equal, toItem: (Your view NAme), attribute: .CenterX, multiplier: 1, constant: 0) self.view.addConstraint(xCenterConstraint) yCenterConstraint = NSLayoutConstraint(item: self.view, attribute: .CenterY, relatedBy: .Equal, toItem: (Your view Name), attribute: .CenterY, multiplier: 1, constant: 0) self.view.addConstraint(yCenterConstraint) 

Answer 7

它在xcode 7.3.1中有点不同。 这是我想出的

  // creating the view let newView = UIView() newView.backgroundColor = UIColor.redColor() newView.translatesAutoresizingMaskIntoConstraints = false view.addSubview(newView) // creating the constraint // attribute and relation cannot be set directyl you need to create a cariable of them let layout11 = NSLayoutAttribute.CenterX let layout21 = NSLayoutRelation.Equal let layout31 = NSLayoutAttribute.CenterY let layout41 = NSLayoutAttribute.Width let layout51 = NSLayoutAttribute.Height let layout61 = NSLayoutAttribute.NotAnAttribute // defining all the constraint let horizontalConstraint = NSLayoutConstraint(item: newView, attribute: layout11, relatedBy: layout21, toItem: view, attribute: layout11, multiplier: 1, constant: 0) let verticalConstraint = NSLayoutConstraint(item: newView, attribute: layout31, relatedBy: layout21, toItem: view, attribute: layout31, multiplier: 1, constant: 0) let widthConstraint = NSLayoutConstraint(item: newView, attribute: layout41, relatedBy: layout21, toItem: nil, attribute: layout61, multiplier: 1, constant: 100) let heightConstraint = NSLayoutConstraint(item: newView, attribute: layout51, relatedBy: layout21, toItem: nil, attribute: layout61, multiplier: 1, constant: 100) // adding all the constraint NSLayoutConstraint.activateConstraints([horizontalConstraint,verticalConstraint,widthConstraint,heightConstraint]) 

Answer 8

您将所有定义的约束添加到newView是错误的，因为宽度和高度约束应添加到您的newView 。

另外，据我所知你想设置恒定的宽度和高度100：100。 在这种情况下，您应该将您的代码更改为：

 var constW = NSLayoutConstraint(item: newView, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 100) newView.addConstraint(constW) var constH = NSLayoutConstraint(item: newView, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: 100) newView.addConstraint(constH) 

Answer 9

这是以编程方式添加约束的一种方法

 override func viewDidLoad() { super.viewDidLoad() let myLabel = UILabel() myLabel.labelFrameUpdate(label: myLabel, text: "Welcome User", font: UIFont(name: "times new roman", size: 40)!, textColor: UIColor.red, textAlignment: .center, numberOfLines: 0, borderWidth: 2.0, BorderColor: UIColor.red.cgColor) self.view.addSubview(myLabel) let myLabelhorizontalConstraint = NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.centerX, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.centerX, multiplier: 1, constant: 0) let myLabelverticalConstraint = NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.centerY, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.centerY, multiplier: 1, constant: 0) let mylabelLeading = NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.leading, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.leading, multiplier: 1, constant: 10) let mylabelTrailing = NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.trailing, relatedBy: NSLayoutRelation.equal, toItem: self.view, attribute: NSLayoutAttribute.trailing, multiplier: 1, constant: -10) let myLabelheightConstraint = NSLayoutConstraint(item: myLabel, attribute: NSLayoutAttribute.height, relatedBy: NSLayoutRelation.equal, toItem: nil, attribute: NSLayoutAttribute.notAnAttribute, multiplier: 1, constant: 50) NSLayoutConstraint.activate(\[myLabelhorizontalConstraint, myLabelverticalConstraint, myLabelheightConstraint,mylabelLeading,mylabelTrailing\]) } extension UILabel { func labelFrameUpdate(label:UILabel,text:String = "This is sample Label",font:UIFont = UIFont(name: "times new roman", size: 20)!,textColor:UIColor = UIColor.red,textAlignment:NSTextAlignment = .center,numberOfLines:Int = 0,borderWidth:CGFloat = 2.0,BorderColor:CGColor = UIColor.red.cgColor){ label.translatesAutoresizingMaskIntoConstraints = false label.text = text label.font = font label.textColor = textColor label.textAlignment = textAlignment label.numberOfLines = numberOfLines label.layer.borderWidth = borderWidth label.layer.borderColor = UIColor.red.cgColor } }