MVC、MVP、MVVM 理解简述

一、 模式的历史 —— 解决复杂的GUI应用的代码组织问题

所以这些都是为了搞定GUI的繁琐的代码组织、职责划分问题

1. MVC

• Controller: 管理所有的业务,等待View发请求，更新代码致Model

• View：请求发送给Controller，也可以直接更新Model（Model通过事件也可以更新View）

• Model：接受来自Controller的请求，也有View的请求，

• 问题：View和model直接存在依赖关系，View又和Controller存在依赖，导致职责并不单一
  

  image.png

import UIKit

struct Person { // Model
    let firstName: String
    let lastName: String
}

class GreetingViewController : UIViewController { // View + Controller
    var person: Person!
    let showGreetingButton = UIButton()
    let greetingLabel = UILabel()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.showGreetingButton.addTarget(self, action: "didTapButton:", forControlEvents: .TouchUpInside)
    }
    
    func didTapButton(button: UIButton) {
        let greeting = "Hello" + " " + self.person.firstName + " " + self.person.lastName
        self.greetingLabel.text = greeting
        
    }
    // layout code goes here
}
// Assembling of MVC
let model = Person(firstName: "David", lastName: "Blaine")
let view = GreetingViewController()

2. MVP

MVC的改良版本 —— 解决View耦合较高的问题，将大部分处理放置于Presenter中

• Presenter：接受View的请求，更新Model数据，也通过IView的接口来更新View
• View：提供更新自己页面的接口，交互请求Presenter
• Model：接受来自Presenter的请求，更新数据也发送给Presenter

image.png

import UIKit

struct Person { // Model
    let firstName: String
    let lastName: String
}

protocol GreetingView: class {
    func setGreeting(greeting: String)
}

protocol GreetingViewPresenter {
    init(view: GreetingView, person: Person)
    func showGreeting()
}

class GreetingPresenter : GreetingViewPresenter {
    unowned let view: GreetingView
    let person: Person
    required init(view: GreetingView, person: Person) {
        self.view = view
        self.person = person
    }
    func showGreeting() {
        let greeting = "Hello" + " " + self.person.firstName + " " + self.person.lastName
        self.view.setGreeting(greeting)
    }
}

class GreetingViewController : UIViewController, GreetingView {
    var presenter: GreetingViewPresenter!
    let showGreetingButton = UIButton()
    let greetingLabel = UILabel()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.showGreetingButton.addTarget(self, action: "didTapButton:", forControlEvents: .TouchUpInside)
    }
    
    func didTapButton(button: UIButton) {
        self.presenter.showGreeting()
    }
    
    func setGreeting(greeting: String) {
        self.greetingLabel.text = greeting
    }
    
    // layout code goes here
}
// Assembling of MVP
let model = Person(firstName: "David", lastName: "Blaine")
let view = GreetingViewController()
let presenter = GreetingPresenter(view: view, person: model)
view.presenter = presenter

3. MVVM

MVP的改良版本 —— 解决Presenter要显示调用IView接口的问题，转而使用实现好的Data Binding Engine（类似于get；set；）

• VM ：存储的数据及状态，其本身存储在ViewLogic这里，接受View的更改请求，也接受model的更改，自动渲染到View
• View：单纯的展示数据和绑定VM，等待VM的变化导致其View发生变化
• Model: 与VM交互，VM更新Model，然后Model更改后会更新VM，从而由 Data Binding Engine来更新View

MVVM示例图1
MVVM示例图2

import UIKit

struct Person { // Model
    let firstName: String
    let lastName: String
}

protocol GreetingViewModelProtocol: class {
    var greeting: String? { get }
    var greetingDidChange: ((GreetingViewModelProtocol) -> ())? { get set } // function to call when greeting did change
    init(person: Person)
    func showGreeting()
}

class GreetingViewModel : GreetingViewModelProtocol {
    let person: Person
    var greeting: String? {
        didSet {
            self.greetingDidChange?(self)
        }
    }
    var greetingDidChange: ((GreetingViewModelProtocol) -> ())?
    required init(person: Person) {
        self.person = person
    }
    func showGreeting() {
        self.greeting = "Hello" + " " + self.person.firstName + " " + self.person.lastName
    }
}

class GreetingViewController : UIViewController {
    var viewModel: GreetingViewModelProtocol! {
        didSet {
            self.viewModel.greetingDidChange = { [unowned self] viewModel in
                self.greetingLabel.text = viewModel.greeting
            }
        }
    }
    let showGreetingButton = UIButton()
    let greetingLabel = UILabel()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.showGreetingButton.addTarget(self.viewModel, action: "showGreeting", forControlEvents: .TouchUpInside)
    }
    // layout code goes here
}
// Assembling of MVVM
let model = Person(firstName: "David", lastName: "Blaine")
let viewModel = GreetingViewModel(person: model)
let view = GreetingViewController()
view.viewModel = viewModel