**优点：**
- 低耦合
- 可重用性
- 独立开发
- 可测试： 针对viewmodel测试
  
    //
    //  ViewController.swift
    //  GA_MVC
    //
    //  Created by houjianan on 2017/3/15.
    //  Copyright © 2017年 houjianan. All rights reserved.
    //
    
    import UIKit
    
    // Controller
    class ViewController: UIViewController {
    
        private lazy var viewModel: ViewModel = ViewModel()
        
        private lazy var myView: MyView = {
            let v = MyView(frame: CGRect(x: 100, y: 100, width: 200, height: 40), handler: {
                [weak self] in
                if let weakSelf = self {
                    weakSelf.loadData(name: "GA_清风又来")
                }
            })
            return v
        }()
        
        override func viewDidLoad() {
            super.viewDidLoad()
            
            self.view.addSubview(myView)
            
            loadData(name: "GA_清风自来")
        }
        
        private func loadData(name: String) {
            viewModel.reloadData(name: name, over: {
                [weak self] in
                if let weakSelf = self {
                    weakSelf.myView.model = weakSelf.viewModel.model
                }
            })
        }
        
    }
    // View
    class MyView: UIView {
        // 别名闭包
        typealias Handler = () -> ()
        var handler: Handler!
        // 传入view的模型
        var model: Model? {
            didSet {
                //更新UI
                nameLabel.text = model?.name
            }
        }
        // 创建UI对象Label
        lazy var nameLabel: UILabel = {
            let l = UILabel(frame: self.bounds)
            l.textColor = UIColor.white
            l.textAlignment = .center
            self.addSubview(l)
            return l
        }()
      
        convenience init(frame: CGRect, handler: @escaping () -> ()) {
            self.init(frame: frame)
            createUI()
            self.handler = handler
        }
        
        private func createUI() {
            self.backgroundColor = UIColor.orange
            self.layer.borderColor = UIColor.brown.cgColor
            self.layer.borderWidth = 2.0
        }
        // view的点击事件，事件传到controller，可用：代理，通知，闭包。
        override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
            self.handler()
        }
    }
    // Model
    class Model {
        var name: String!
        
        init(name: String) {
            self.name = "名字:" + name
        }
    }
    
    class ViewModel {
        
        var model: Model?
        
        public func reloadData(name: String, over: @escaping () -> ()) {
            // 模拟网络请求
            let time = DispatchTime.now() + Double(Int64(2 * 1000 * 1000000)) / Double(NSEC_PER_SEC)
            DispatchQueue.global().asyncAfter(deadline: time, execute: {
                let model = Model(name: name)
                DispatchQueue.main.async {
                    [weak self] in
                    if let weakSelf = self {
                        weakSelf.model = model
                        over()
                    }
                }
            })
        }
    }