🚀Comprehensive Redux library for SwiftUI, ensures State consistency across Stores with type-safe pub/sub pattern.

Cheng Zhang

Last update: Mar 9, 2022

Related tags

Overview

SwiftUIRedux

Comprehensive Redux library for SwiftUI.

Keep State consistent across Stores by type safe pub/sub pattern with Reducers of RootStore.
Waterfall Action propagation flow from root to State subtree.

Unidirectional Data Flow

RootStore/Dispatcher: Propagates domained actions
Reducer: Subscribes to RootStore and reduces Action to generate new state
Action: Action driven - more loosely coupled pattern than Delegation pattern
State:
- Reduces Action and outputs new State
- Waterfall reduce flow: propagates Action to children nodes via State tree

Declarative/Stateful/Immutable/Predictable

Efficient tree diff algorithm, no more imperative manual update code.

Usage Example

FeedListView

struct FeedListView: View {
  @ObservedObject var state = FeedListState()
  
  var body: some View {
    List {
      ForEach(state.feeds, id: \.diffId) { feed in
        FeedCell(feed: feed)
      }
    }
  }
}

FeedListState

public class FeedListState: ReduxReducer, ObservableObject {  
  @Published var feeds: [Feed] = []
  
  public override func reduce(action: ReduxActionProtocol) {
    // Propagates `action` to the substate tree.
    // Setting `self.feeds` with new feeds triggers list UI reloading 
    // and SwiftUI will diff efficiently based on list identifier.
    feeds = feeds.map { $0.reduce(action: action) }
}

Dispatch FeedLikeAction

dispatch(action: FeedLikeAction(feed: feed))

Reduce FeedLikeAction

public struct Feed {
  public var diffId = UUID()
  public let feedId: Int
  public let title: String
  public var isLiked: Bool { didSet { diffId = UUID() } }     
}

extension Feed: ReduxStateProtocol {
  @discardableResult
  public func reduce(action: ReduxActionProtocol) -> Self {
    // Makes the deep copy of self.
    var feedCopy = self    
    switch action {
    case let action as FeedLikeAction:
      // Reduces the `FeedLikeAction`.
      if feedId == action.feed.feedId {
        feedCopy.isLiked = !action.feed.isLiked
      }
    default: break
    }
    return feedCopy
  }
}

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Comments

Reduce(action:) mutates the same model instance twice, if model is Reference Type

Example

If FeedList/FeedDetails shares the same Feed reference, LikeFeed action in FeedDetails will possibly mutate Feed instance twice by both reduce(action:) in FeedDetailsState and FeedListState.

Solution

Recommendation is to define conformance as struct and return deep copy of self, e.g. var newSelf = self, to avoid duplicate mutations on the same model if with reference type.

Workaround is to return complete deep copy of the instance if you have to use Reference type.
bug

opened by geekaurora 1