RxState: Redux + RxSwift

RxState a predictable state container for Swift apps. It's a tiny library built on top of RxSwift and inspired by Redux that facilitates building Unidirectional Data Flow architecture.

Why Unidirectional Data Flow Architecture?

1. Helps you manage state in a consistent and unified way that guaranty it’s always predictable (After all, state is the source of all evil and you wanna keep that evil in check).
2. Limits the way app state can be mutated, which makes your app easier to understand.
3. Makes your code easy to test.
4. Enables faster debugging.
5. It’s is entirely platform independent - you can easily use the same business logic and share it between apps for multiple platforms (iOS, tvOS, etc.).

Architecture Components

• App State: A single immutable data structure. It includes the UI state, the navigation state and the state of your model layer.

• Store:Contains the app state and notifies the App State Observers of the App State updates.

• Reducer: A pure function that takes the current app state and an Action as input, creates a new App State that reflects the changes described by the Action, and returns the new App State.

• Action: Actions describe a state change. The only way to modified the App State is by dispatching Actions to the Store.

• Action Creators and Dispatchers: Creates Actions and dispatch them to the store.

• App State Observers: Observers the App State in the Store to transform it to presentable data, write logs, etc.

• View: Presents the presentable data that was deriver from the App State and delivers the user's interactions to the Action Creators and Dispatchers.

How it works?

1. The View/View Controller sends events (The View Model's inputs) to the View Model.

2. The View Model creates an Action from the received inputs and dispatch them to the Store.

• The View Model can use a dedicated Action Creators to create Actions. Action Creators do can async work and, based on the results it gets, returns different Actions to the View Model to dispatch.

3. The Store sends the App State and the received Action to the Reducer.

4. The Reducer receives the current App State and the dispatched Action, computes and returns new App State.

5. The Store sends the new App State to the subscribers.

• One of the subscribers could be a Middleware that logs the App State resulted from dispatching an Action.

6. The View Model receives the new App State, transform it presentable data, and send it to the View/View Controller.

• The View Model can use Transformers to transform the App State to presentable data. This helps you reuse the transformation code in different View Models.

7. The View/View Controller render the UI to show the presentable data to the user.

How does RxState helps you build the Architecture?

RxState defines the main component for you:

1. Store: Contains the App State in the form of Driver<[SubstateType]>.

2. SubstateType: A protocol that tags structs representing a substate. Ex.

struct TasksState: SubstateType {   
    var tasks: [Task]
    var addingTask: Bool
}

You can add a Substates to the App State by dispatching StoreAction.add(states: [SubstateType]).

let tasksState = TasksState()
let action = StoreAction.add(states: [tasksState])
store.dispatch(action: action)

3. ActionType: A protocol that tags an Action. The Store has the following Actions:

public enum StoreAction: ActionType {
    /// Adds substates to the application state.
    case add(states: [SubstateType])

    /// Removes all substates in the application state.
    case reset
}

4. MainReducer: A reducer used by the Store's dispatch function to call the respective reducer based on the Action type.

let mainReducer: MainReducer = { (state: [SubstateType], action: ActionType) -> [SubstateType] in
    // Copy the `App State`
    var state: [SubstateType] = state
    
    // Cast to a specific `Action`.
    switch action {
    case let action as TasksAction:

        // Extract the `Substate`.
        guard var (tasksStateIndex, tasksState) = state
            .enumerated()
            .first(where: { (_, substate: SubstateType) -> Bool in
                return substate is Store.TasksState}
            ) as? (Int, Store.TasksState)
            else {
                fatalError("You need to register `TasksState` first")
        }

        // Reduce the `Substate` to get a new `Substate`.
        tasksState = Store.reduce(state: tasksState, action: action)
    
        // Replace the `Substate` in the `App State` with the new `Substate`.
        state[tasksStateIndex] = tasksState as SubstateType
    
    default:
        fatalError("Unknown action type")
    }
    
    // Return the new `App State`
    return state
}

4. MiddlewareType: A protocol defining an object that can observe the App State and the last dispatched Action and does something with it like logging:

protocol LoggingMiddlewareType: Middleware, HasDisposeBag {}

final class LoggingMiddleware: LoggingMiddlewareType {
    var disposeBag = DisposeBag()

    func observe(currentStateLastAction: Driver<CurrentStateLastAction>) {
        currentStateLastAction
            .drive(
                onNext: { (currentState: [SubstateType], lastAction: ActionType?) in
                    print(currentState)
                    print(lastAction)
                }, onCompleted: nil, onDisposed: nil)
            .disposed(by: disposeBag)
        }
    }
}

Dependencies

• RxSwift (>= 5.1)
• RxCocoa (>= 5.1)

Requirements

• Swift 5

Installation

• Using CocoaPods:

pod 'RxState'

• Using Swift Package Manager:

Create a Package.Swift file in your project's root folder.

Add following content into the Package.swift file

// swift-tools-version:5.0

import PackageDescription

let package = Package(
  name: "YourProjectName",
  dependencies: [
    .package(url: "https://github.com/RxSwiftCommunity/RxState.git", from: "0.6.0")
  ],
  targets: [
    .target(name: "YourProjectTarget", dependencies: ["RxState"])
  ]
)

Demo

I have tried to make the demo app as comprehensive as possible. It currently runs on iOS and macOS. Notice how, because of the architecture, only the View/ View Controller layer needed to change in order to port the app from iOS to macOS.

Contributing

We would love to see you involved! Feedback and contribution are greatly appreciated :) Checkout the Contributing Guide and the Code of Conduct.

Influences and credits

• RxSwift: Reactive Programming in Swift.
• Redux: a predictable state container for JavaScript apps.

Author

Nazih Shoura, [email protected]

License

This library belongs to RxSwiftCommunity.

RxState is available under the MIT license. See the LICENSE file for more info.