以编程方式设置约束

Boilerplate 代码示例

override func viewDidLoad() {
    super.viewDidLoad()

    let myView = UIView()
    myView.backgroundColor = UIColor.blueColor()
    myView.translatesAutoresizingMaskIntoConstraints = false
    view.addSubview(myView)

    // Add constraints code here
    // ...
}

在下面的示例中，Anchor Style 是 NSLayoutConstraint Style 的首选方法，但它仅适用于 iOS 9，所以如果你支持 iOS 8，那么你仍然应该使用 NSLayoutConstraint Style。

钢钉

锚式

let margins = view.layoutMarginsGuide
myView.leadingAnchor.constraintEqualToAnchor(margins.leadingAnchor, constant: 20).active = true

• 除了 leadingAnchor，还有 trailingAnchor，topAnchor 和 bottomAnchor。

NSLayoutConstraint 风格

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.Leading, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.LeadingMargin, multiplier: 1.0, constant: 20.0).active = true

• 除了 .Leading，还有 .Trailing，.Top 和 .Bottom。
• 除了 .LeadingMargin，还有 .TrailingMargin，.TopMargin 和 .BottomMargin。

视觉格式语言风格

NSLayoutConstraint.constraintsWithVisualFormat("H:|-20-[myViewKey]", options: [], metrics: nil, views: ["myViewKey": myView])

宽度和高度

锚式

myView.widthAnchor.constraintEqualToAnchor(nil, constant: 200).active = true
myView.heightAnchor.constraintEqualToAnchor(nil, constant: 100).active = true

NSLayoutConstraint 风格

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: 200).active = true
NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem: nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1, constant: 100).active = true

视觉格式语言风格

NSLayoutConstraint.constraintsWithVisualFormat("H:[myViewKey(200)]", options: [], metrics: nil, views: ["myViewKey": myView])
NSLayoutConstraint.constraintsWithVisualFormat("V:[myViewKey(100)]", options: [], metrics: nil, views: ["myViewKey": myView])

容器中心

锚式

myView.centerXAnchor.constraintEqualToAnchor(view.centerXAnchor).active = true
myView.centerYAnchor.constraintEqualToAnchor(view.centerYAnchor).active = true

NSLayoutConstraint 风格

NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.CenterX, multiplier: 1, constant: 0).active = true
NSLayoutConstraint(item: myView, attribute: NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: view, attribute: NSLayoutAttribute.CenterY, multiplier: 1, constant: 0).active = true

视觉格式语言风格

NSLayoutConstraint.constraintsWithVisualFormat("V:[viewKey]-(<=0)-[myViewKey]", options: NSLayoutFormatOptions.AlignAllCenterX, metrics: nil, views: ["myViewKey": myView, "viewKey": view])
NSLayoutConstraint.constraintsWithVisualFormat("H:[viewKey]-(<=0)-[myViewKey]", options: NSLayoutFormatOptions.AlignAllCenterY, metrics: nil, views: ["myViewKey": myView, "viewKey": view])