iOS Architecture Patterns
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:
各架构综合对比.png
图中三个对比要素分别为:
- 各实体(指
Views/Models/Controller/Presenter/ViewModel等)之间均摊职责- 代码可测试性
- 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
Apple's MVC.png
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
MVP.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
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
MVVM.png
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
VIPER.png
- 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
- 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.
- 根据业务需求选择架构, 不要为了架构而架构.
- 没有最好的架构, 只有最合适的架构.