iOS开发之进阶篇（13）—— MVC / MVP / MVVM / VIPER 架构

概述

本文基本转译自这篇博文 iOS Architecture Patterns.
事实上, 网上大多数关于讨论这几个架构的博文, 均出自于此.
本文将惜字如金般、直截了当地抛论点, 上代码.
祝各位看官阅读愉快!!

如题, 我们将对 MVC / MVP / MVVM / VIPER 这四个常用iOS架构进行一一讨论.
先来看看它们之间的综合对比:

图中三个对比要素分别为:

1. 各实体(指Views/Models/Controller/Presenter/ViewModel等)之间均摊职责
2. 代码可测试性
3. 易于使用

我们统称MVC / MVP / MVVM为MV(X)派别. 其中MVP、MVVM均由MVC发展而来, 是为了将Controller瘦身而发展成不同的产物. 我们将这三者进行归纳讨论:

• Models — 负责操纵数据(本地或远端), 或指代操纵数据的数据访问层.
• Views — 负责展示内容的视图. 如UIImageView, UILabel等带UI开头的内容.
• Controller/Presenter/ViewModel — View和Model之间的连接"桥梁", 负责将View中的用户行为(如点击某个button)转变为Model, 也将Model的改变通过View表现出来.

VIPER有点不同, 它不属于MV(X)类别. VIPER对职责分离的想法进行了另一次迭代, 将整个架构划分为五个层级, 使得职责的划分更为细致. 对于这五个层级, 我们在后文中再根据图示来一一讨论.

MVC

图中, 上半部分是苹果所期望的MVC的样子, 但由于View和View Controller过度耦合, 导致了实际上我们的MVC的样子看起来更像下半部分.

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()
view.person = model;

三要素:

• Distribution — View和Model虽然分离, 但View和Controller紧耦合.
• Testability — Model易于测试, 而View和Controller难以测试.
• Ease of use — 相较于其他架构, 代码量最小.

MVP

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

三要素:

• Distribution — 职责划分明确
• Testability — 可测试性非常好, 虽然是以使用笨拙的View(VC)作为代价.
• Easy of use — 代码量是MVC的两倍. 但MVP概念清晰.

MVVM

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

三要素:

• Distribution — MVVM的View的责任比MVP的View的责任更大
• Testability — View Model不关心View的实现, 因此易于测试
• Easy of use — MVVM的代码量与MVP相当.

绑定
绑定对于OS X开发是开箱即用的，但是我们在iOS工具箱中没有绑定。当然，我们有KVO和通知，但它们不如绑定方便。

因此，如果我们不想自己编写它们，我们有两个选择：

• 基于KVO的绑定库之一，例如RZDataBinding或SwiftBond
• 全规模函数反应性编程巨兽，例如ReactiveCocoa，RxSwift或PromiseKit

VIPER

• Interactor — 交互器. 包含与数据（实体）或网络相关的业务逻辑，例如创建实体的新实例或从服务器获取它们。为此，您将使用一些服务和管理器，这些服务和管理器不被视为VIPER模块的一部分，而是外部依赖项。
• Presenter — 包含UI相关(但独立于UIKit)的业务逻辑，调用Interactor上的方法。
• Entities — 普通数据对象，而不是数据访问层，因为这是交互者的职责。
• Router — 负责VIPER 模块之间的隔离。
• View — UI展示. 包括View和VC.

import UIKit

struct Person { // Entity (usually more complex e.g. NSManagedObject)
    let firstName: String
    let lastName: String
}

struct GreetingData { // Transport data structure (not Entity)
    let greeting: String
    let subject: String
}

protocol GreetingProvider {
    func provideGreetingData()
}

protocol GreetingOutput: class {
    func receiveGreetingData(greetingData: GreetingData)
}

class GreetingInteractor : GreetingProvider {
    weak var output: GreetingOutput!
    
    func provideGreetingData() {
        let person = Person(firstName: "David", lastName: "Blaine") // usually comes from data access layer
        let subject = person.firstName + " " + person.lastName
        let greeting = GreetingData(greeting: "Hello", subject: subject)
        self.output.receiveGreetingData(greeting)
    }
}

protocol GreetingViewEventHandler {
    func didTapShowGreetingButton()
}

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

class GreetingPresenter : GreetingOutput, GreetingViewEventHandler {
    weak var view: GreetingView!
    var greetingProvider: GreetingProvider!
    
    func didTapShowGreetingButton() {
        self.greetingProvider.provideGreetingData()
    }
    
    func receiveGreetingData(greetingData: GreetingData) {
        let greeting = greetingData.greeting + " " + greetingData.subject
        self.view.setGreeting(greeting)
    }
}

class GreetingViewController : UIViewController, GreetingView {
    var eventHandler: GreetingViewEventHandler!
    let showGreetingButton = UIButton()
    let greetingLabel = UILabel()

    override func viewDidLoad() {
        super.viewDidLoad()
        self.showGreetingButton.addTarget(self, action: "didTapButton:", forControlEvents: .TouchUpInside)
    }
    
    func didTapButton(button: UIButton) {
        self.eventHandler.didTapShowGreetingButton()
    }
    
    func setGreeting(greeting: String) {
        self.greetingLabel.text = greeting
    }
    
    // layout code goes here
}
// Assembling of VIPER module, without Router
let view = GreetingViewController()
let presenter = GreetingPresenter()
let interactor = GreetingInteractor()
view.eventHandler = presenter
presenter.view = view
presenter.greetingProvider = interactor
interactor.output = presenter

三要素:

• Distribution — 职责分配最优者 (相较于另外三种架构).
• Testability — 最好的可测试性 (相较于另外三种架构).
• Easy of use — 代码量巨大 (接口多).

结语

1. 大胆地在同一工程中混合使用不同的MV(X)架构, 它们本身的兼容性很好.
2. 根据业务需求选择架构, 不要为了架构而架构.
3. 没有最好的架构, 只有最合适的架构.