Xcode8已经发布，带了Swift3的预览版本，以后都是默认采用Swift3的语法。

这个例子主要是演示iOS中如何用纯代码实现自动布局，先看看效果。

还是先创建程序入口文件main.swift:

import UIKit

let argc = Process.argc
let argv = UnsafeMutablePointer<UnsafeMutablePointer<CChar>>(Process.unsafeArgv)

UIApplicationMain(argc,argv,NSStringFromClass(MainApp),NSStringFromClass(MainAppDelegate))

创建UI程序入口App.swift，增加了一个导航栏：

import UIKit

class MainApp: UIApplication {
	override func sendEvent(_ event: UIEvent) {
		super.sendEvent(event)
	}
}

class MainAppDelegate: UIResponder,UIApplicationDelegate {
	
	var window: UIWindow?
	
	func application(_ app: UIApplication,didFinishLaunchingWithOptions opt: [NSObject: AnyObject]?) -> Bool {
		
		self.window = UIWindow(frame: UIScreen.main().bounds)

		self.window!.rootViewController = UINavigationController(rootViewController:MainViewController())
		self.window!.backgroundColor = UIColor.white()
		self.window!.makeKeyAndVisible()
		
		return true
	}
}

然后创建视图控制器ViewController.swift,在这里实现自动布局：

import UIKit

class MainViewController: UIViewController {

	var label0_: UILabel!
	var label1_: UILabel!
	var label2_: UILabel!

	override func viewDidLoad() {
		super.viewDidLoad()
		
		self.title = "主视图"

		self.label0_ = {
			let label = UILabel()
			label.textAlignment = .center
			label.text = "Hello,AutoLayout!"
			return label
		}()

		self.label1_ = {
			let label = UILabel()
			label.textColor = UIColor.red()
			label.textAlignment = .center
			label.text = "=== 你好,AutoLayout! ==="
			return label
		}()
		
		self.label2_ = {
			let label = UILabel()
			label.textColor = UIColor.blue()
			label.textAlignment = .center
			label.text = "=== 底部 ==="
			return label
		}()

		self.view.addSubview(self.label0_)
		self.view.addSubview(self.label1_)
		self.view.addSubview(self.label2_)

		self.view.setupAutoLayout {
			return (
				layputs: [
					("H:|-(20)-[label0]-20-|",[]),("H:|-(20)-[label1]-20-|",("H:|-(20)-[label2]-20-|",("V:|[topGuide]-(0)-[label0(20)]-20-[label1(20)]-(>=0)-[label2]-[bottomGuide]|",[])
				],viewsMap: [
					"topGuide": self.topLayoutGuide,"bottomGuide": self.bottomLayoutGuide,"label0": self.label0_,"label1": self.label1_,"label2": self.label2_
				]
			)
		}
	}
}

其中self.view.setupAutoLayout是针对UIView类型作的扩展:

extension UIView {
	func setupAutoLayout(closure: () -> (layouts: [(String,NSLayoutFormatOptions)],viewsMap: [String:AnyObject]) ) {
		let (viewsLayouts,viewsMap) = closure()
		
		// 采用自动布局
		for view in viewsMap.values {
			if let v = view as? UIView {
				v.translatesAutoresizingMaskIntoConstraints = false
			}
		}
		
		// 添加自动布局规则
		for layout in viewsLayouts {
			self.addConstraints(
				NSLayoutConstraint.constraints(
					withVisualFormat: layout.0,options: layout.1,metrics: nil,views: viewsMap
				)
			)
		}
	}
}

完成。