self.view.addSubview(label1)
// Do any additional setup after loading the view, typically from a nib.
label1.text = "123你好啊？?"
label1.setTranslatesAutoresizingMaskIntoConstraints(false)
var constraints = [NSLayoutConstraint]()
NSLayoutConstraint.constraintsWithVisualFormat("[label1]-20-|",options:NSLayoutFormatOptions.allZeros,metrics: nil,views: ["label1": label1!]).map {
    constraints.append($0 as NSLayoutConstraint)
}
self.view.addConstraints(constraints)

需要注意，一定要先将元素放到view当中，才能触发。否则会报错。

几种格式：
Standard Space: [button]-[textField]
Width Constraint: [button(>=50)]
Connection to Superview: |-50-[purpleBox]-50-|
Vertical Layout: V:[topField]-10-[bottomField]
Flush Views: [maroonView][blueView]
Priority: [button(100@20)]
Equal Widths: [button1(==button2)]
Multiple Predicates: [flexibleButton(>=70,<=100)]
A Complete Line of Layout: |-[find]-[findNext]-[findField(>=20)]-|

这样制作的时候就可以通用于 3.5/4/4.7/5.5 寸的屏幕。

好像是只适用于IOS6+ 。