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https://github.com/sergdort/CombineFeedback
Unidirectional reactive architecture using new Apple Combine framework https://developer.apple.com/documentation/combine
https://github.com/sergdort/CombineFeedback
architecture combine swift swiftui unidirectional
Last synced: about 2 months ago
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Unidirectional reactive architecture using new Apple Combine framework https://developer.apple.com/documentation/combine
- Host: GitHub
- URL: https://github.com/sergdort/CombineFeedback
- Owner: sergdort
- License: mit
- Created: 2019-06-07T06:22:44.000Z (over 5 years ago)
- Default Branch: master
- Last Pushed: 2021-11-23T12:59:46.000Z (almost 3 years ago)
- Last Synced: 2024-05-22T15:32:48.717Z (4 months ago)
- Topics: architecture, combine, swift, swiftui, unidirectional
- Language: Swift
- Size: 13.8 MB
- Stars: 689
- Watchers: 20
- Forks: 54
- Open Issues: 12
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
- awesome-combine - Combine Feedback
- fucking-about-SwiftUI - CombineFeedback
README
# CombineFeedback
Unidirectional Reactive Architecture. This is a [Combine](https://developer.apple.com/documentation/combine) implemetation of [ReactiveFeedback](https://github.com/Babylonpartners/ReactiveFeedback) and [RxFeedback](https://github.com/kzaher/RxFeedback)
## Diagram
## Motivation
Requirements for iOS apps have become huge. Our code has to manage a lot of state e.g. server responses, cached data, UI state, routing etc. Some may say that Reactive Programming can help us a lot but, in the wrong hands, it can do even more harm to your code base.
The goal of this library is to provide a simple and intuitive approach to designing reactive state machines.
## Core Concepts
### State
`State` is the single source of truth. It represents a state of your system and is usually a plain Swift type. Your state is immutable. The only way to transition from one `State` to another is to emit an `Event`.
### Event
Represents all possible events that can happen in your system which can cause a transition to a new `State`.
### Reducer
A Reducer is a pure function with a signature of `( inout State, Event) -> Void`. While `Event` represents an action that results in a `State` change, it's actually not what _causes_ the change. An `Event` is just that, a representation of the intention to transition from one state to another. What actually causes the `State` to change, the embodiment of the corresponding `Event`, is a Reducer. A Reducer is the only place where a `State` can be changed.
### Feedback
While `State` represents where the system is at a given time, `Event` represents a state change, and a `Reducer` is the pure function that enacts the event causing the state to change, there is not as of yet any type to decide which event should take place given a particular current state. That's the job of the `Feedback`. It's essentially a "processing engine", listening to changes in the current `State` and emitting the corresponding next events to take place. Feedbacks don't directly mutate states. Instead, they only emit events which then cause states to change in reducers.
To some extent it's like reactive [Middleware](https://redux.js.org/advanced/middleware) in [Redux](https://redux.js.org)
### Dependency
Dependency is the type that holds all services that feature needs, such as API clients, analytics clients, etc.
#### Store
Store - is a base class responsible for initializing a UI state machine. It provides two ways to interact with it.
- We can start a state machine by observing `var state: AnyPublisher`.
- We can send input events into it via `public final func send(event: Event)`.
This is useful if we want to mutate our state in response to user input. Let's consider a `Counter` example
```swift
struct State {
var count = 0
}
enum Event {
case increment
case decrement
}
```
When we press **+** button we want the `State` of the system to be incremented by `1`. To do that somewhere in our UI we can do:
```swift
Button(action: {
store.send(event: .increment)
}) {
return Text("+").font(.largeTitle)
}
```
Also, we can use the `send(event:)` method to initiate side effects. For example, imagine that we are building an infinite list, and we want to trigger the next batch load when a user reaches the end of the list.
```swift
enum Event {
case didLoad(Results)
case didFail(Error)
case fetchNext
}
struct State: Builder {
var batch: Results
var movies: [Movie]
var status: Status
}
enum Status {
case idle
case loading
case failed(Error)
}
struct MoviesView: View {
typealias State = MoviesViewModel.State
typealias Event = MoviesViewModel.Event
let context: Context
var body: some View {
List {
ForEach(context.movies.identified(by: \.id)) { movie in
MovieCell(movie: movie).onAppear {
// When we reach the end of the list
// we send `fetchNext` event
if self.context.movies.last == movie {
self.context.send(event: .fetchNext)
}
}
}
}
}
}
```
When we send `.fetchNext` event, it goes to the `reducer` where we put our system into `.loading` state, which in response triggers effect in the `whenLoading` feedback, which is reacting to particular state changes
```swift
static func reducer(state: inout State, event: Event) {
switch event {
case .didLoad(let batch):
state.movies += batch.results
state.status = .idle
state.batch = batch
case .didFail(let error):
state.status = .failed(error)
case .retry:
state.status = .loading
case .fetchNext:
state.status = .loading
}
}
static var feedback: Feedback {
return Feedback(lensing: { $0.nextPage }) { page in
URLSession.shared
.fetchMovies(page: page)
.map(Event.didLoad)
.replaceError(replace: Event.didFail)
.receive(on: DispatchQueue.main)
}
}
```
#### Composition
Taking inspiration from [TCA](https://github.com/pointfreeco/swift-composable-architecture) `CombineFeedback` is build with a composition in mind.
Meaning that we can compose smaller states into bigger states. For more details please see Example App.
#### ViewContext
`ViewContext` - is a rendering context that we can use to interact with UI and render information. Via `@dynamicMemberLookup` it has all of the properties of the `State` and several conveniences methods for more seamless integration with SwiftUI. (Credits to [@andersio](https://github.com/andersio))
```swift
struct State {
var email = ""
var password = ""
}
enum Event {
case signIn
}
struct SignInView: View {
private let store: Store
init(store: Store) {
self.store = store
}
var body: some View {
WithContextView(store: store) { context in
Form {
Section {
TextField(context.binding(for: \.email, event: Event.emailDidChange))
TextField(context.binding(for: \.password, event: Event.passwordDidCange))
Button(action: context.action(for: .signIn)) {
Text("Sign In")
}
}
}
}
}
}
```
### Example
| Counter | Infinite List | SignIn Form | Traffic Light |
| --- | --- | --- | --- |
|
| 
| 
| 
### References
[Automata theory](https://en.wikipedia.org/wiki/Automata_theory)
[TCA](https://github.com/pointfreeco/swift-composable-architecture)
[Finite-state machine](https://en.wikipedia.org/wiki/Finite-state_machine)
[Mealy machine](https://en.wikipedia.org/wiki/Mealy_machine)