# 7.3 ReactorKit

![](/files/-MWlwPGiT5wcZNFkqMtJ)

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## 作者

[Jeon Suyeol](https://github.com/devxoul) 是 [ReactorKit](https://github.com/ReactorKit/ReactorKit) 的作者。他也发布了一些富有创造性的框架，如 [Then](https://github.com/devxoul/Then)，[URLNavigator](https://github.com/devxoul/URLNavigator)，[SwiftyImage](https://github.com/devxoul/SwiftyImage) 以及一些开源项目 [RxTodo](https://github.com/devxoul/RxTodo)，[Drrrible](https://github.com/devxoul/Drrrible)。他也是多个组织的成员 [RxSwiftCommunity](https://github.com/RxSwiftCommunity)，[Moya](https://github.com/Moya)，[SwiftKorea](https://github.com/SwiftKorea)。

## 介绍

[ReactorKit](https://github.com/ReactorKit/ReactorKit) 结合了 [Flux](https://facebook.github.io/flux/) 和[响应式编程](https://zh.wikipedia.org/wiki/响应式编程)。用户行为和页面状态都是通过序列相互传递。这些序列都是单向的：页面只能发出用户行为，然而反应器（Reactor）只能发出状态。

![](/files/-MWlwPGjyVh4xTO_n0-8)

## View

**View** 用于展示数据。`ViewController` 和 `Cell` 都可以看作是 **View**。**View** 将用户输入绑定到 **Action** 的序列上，同时将页面状态绑定到 UI 组件上。

定义一个 **View** 只需要让它遵循 `View` 协议即可。然后你的类将自动获得一个 `reactor` 属性。这个属性应该在 **View** 的外面被设置：

```swift
class ProfileViewController: UIViewController, View {
  var disposeBag = DisposeBag()
}

profileViewController.reactor = UserViewReactor() // 注入 reactor
```

当 `reactor` 属性被设置时，`bind(reactor:)` 方法就会被调用。执行这个方法来进行用户输入绑定和状态输出绑定。

```swift
func bind(reactor: ProfileViewReactor) {
  // action (View -> Reactor)
  refreshButton.rx.tap.map { Reactor.Action.refresh }
    .bind(to: reactor.action)
    .disposed(by: self.disposeBag)

  // state (Reactor -> View)
  reactor.state.map { $0.isFollowing }
    .bind(to: followButton.rx.isSelected)
    .disposed(by: self.disposeBag)
}
```

## Reactor

**Reactor** 是与 UI 相互独立的一层，主要负责状态管理。**Reactor** 最重要的作用就是将业务逻辑从 **View** 中抽离。每一个 **View** 都有对应的 **Reactor** 并且将所有的逻辑代理给 **Reactor**。**Reactor** 不需要依赖 **View**，所以它很容易被测试。

遵循 `Reactor` 协议即可定义一个 **Reactor**。这个协议需要定义三个类型：`Action`，`Mutation` 和 `State`。它也需要一个 `initialState` 属性。

```swift
class ProfileViewReactor: Reactor {
  // 代表用户行为
  enum Action {
    case refreshFollowingStatus(Int)
    case follow(Int)
  }

  // 代表附加作用
  enum Mutation {
    case setFollowing(Bool)
  }

  // 代表页面状态
  struct State {
    var isFollowing: Bool = false
  }

  let initialState: State = State()
}
```

**Action** 代表用户行为，**State** 代表页面状态。**Mutation** 是 **Action** 和 **State** 的桥梁。**Reactor** 通过两步将**用户行为序列**转换为**页面状态序列**：`mutate()` 和 `reduce()`。

![](/files/-MWlwPGl3jlaDHwOgOVD)

**mutate()**

`mutate()` 接收一个 **Action** ，然后创建一个 `Observable<Mutation>`。

```swift
func mutate(action: Action) -> Observable<Mutation>
```

每种[附加作用](/rxswift/recipes/side_effects.md)，如，异步操作，API 调用都是在这个方法内执行。

```swift
func mutate(action: Action) -> Observable<Mutation> {
  switch action {
  case let .refreshFollowingStatus(userID): // receive an action
    return UserAPI.isFollowing(userID) // create an API stream
      .map { (isFollowing: Bool) -> Mutation in
        return Mutation.setFollowing(isFollowing) // convert to Mutation stream
      }

  case let .follow(userID):
    return UserAPI.follow()
      .map { _ -> Mutation in
        return Mutation.setFollowing(true)
      }
  }
}
```

**reduce()**

`reduce()` 通过旧的 **State** 以及 **Mutation** 创建一个新的 **State**。

```swift
func reduce(state: State, mutation: Mutation) -> State
```

这个方法是一个纯函数。它将同步的返回一个 **State**。不会产生其他的作用。

```swift
func reduce(state: State, mutation: Mutation) -> State {
  var state = state // create a copy of the old state
  switch mutation {
  case let .setFollowing(isFollowing):
    state.isFollowing = isFollowing // manipulate the state, creating a new state
    return state // return the new state
  }
}
```

**transform()**

`transform()` 转换每一种序列。有三种转换方法：

```swift
func transform(action: Observable<Action>) -> Observable<Action>
func transform(mutation: Observable<Mutation>) -> Observable<Mutation>
func transform(state: Observable<State>) -> Observable<State>
```

执行这些方法可以转换或者组合其他的序列。例如，`transform(mutation:)` 最适合用来组合一个全局事件，生成一个 **Mutation** 序列。

它也可用来做调试：

```swift
func transform(action: Observable<Action>) -> Observable<Action> {
  return action.debug("action") // Use RxSwift's debug() operator
}
```

## 示例

下一节将用 [Github Search](/rxswift/architecture/reactorkit/github_search.md) 来演示如何使用 [ReactorKit](https://github.com/ReactorKit/ReactorKit)。


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