SwiftUI State Management
CacheStore is a SwiftUI state management framework that uses a dictionary as the state. Scoping creates a single source of truth for the parent state. CacheStore uses c, which a simple composition framework. c has the ability to create transformations that are either unidirectional or bidirectional.
A [AnyHashable: Any] can be used as the single source of truth for an app. Scoping can be done by limiting the known keys. Modification to the scoped value or parent value should be reflected throughout the app.
CacheStore: An object that needs defined Keys to get and set values.Store: An object that needs defined Keys, Actions, and Dependencies. (Preferred)TestStore: A testable wrapper aroundStoreto make it easy to write XCTestCases
A Store is an object that you send actions to and read state from. Stores use a CacheStore to manage state behind the scenes. All state changes must be defined in a StoreActionHandler where the state gets modified depending on an action.
When creating tests you should use TestStore to send and receive actions while making expectations. If any expectation is false it will be reported in a XCTestCase. If there are any effects left at the end of the test, there will be a failure as all effects must be completed and all resulting actions handled. TestStore uses a FIFO (first in first out) queue to manage the effects.
Store Example
import CacheStore
import SwiftUI
struct Post: Codable, Hashable {
var id: Int
var userId: Int
var title: String
var body: String
}
enum StoreKey {
case url
case posts
case isLoading
}
enum Action {
case fetchPosts
case postsResponse(Result<[Post], Error>)
}
extension String: Error { }
struct Dependency {
var fetchPosts: (URL) async -> Result<[Post], Error>
}
extension Dependency {
static var mock: Dependency {
Dependency(
fetchPosts: { _ in
sleep(1)
return .success([Post(id: 1, userId: 1, title: "Mock", body: "Post")])
}
)
}
static var live: Dependency {
Dependency { url in
do {
let (data, _) = try await URLSession.shared.data(from: url)
return .success(try JSONDecoder().decode([Post].self, from: data))
} catch {
return .failure(error)
}
}
}
}
let actionHandler = StoreActionHandler<StoreKey, Action, Dependency> { cacheStore, action, dependency in
switch action {
case .fetchPosts:
struct FetchPostsID: Hashable { }
guard let url = cacheStore.get(.url, as: URL.self) else {
return ActionEffect(.postsResponse(.failure("Key `.url` was not a URL")))
}
cacheStore.set(value: true, forKey: .isLoading)
return ActionEffect(id: FetchPostsID()) {
.postsResponse(await dependency.fetchPosts(url))
}
case let .postsResponse(.success(posts)):
cacheStore.set(value: false, forKey: .isLoading)
cacheStore.set(value: posts, forKey: .posts)
case let .postsResponse(.failure(error)):
cacheStore.set(value: false, forKey: .isLoading)
}
return .none
}
struct ContentView: View {
@ObservedObject var store: Store<StoreKey, Action, Dependency> = .init(
initialValues: [
.url: URL(string: "https://jsonplaceholder.typicode.com/posts")!
],
actionHandler: actionHandler,
dependency: .live
)
.debug
private var isLoading: Bool {
store.get(.isLoading, as: Bool.self) ?? true
}
var body: some View {
if
!isLoading,
let posts = store.get(.posts, as: [Post].self)
{
List(posts, id: \.self) { post in
Text(post.title)
}
} else {
ProgressView()
.onAppear {
store.handle(action: .fetchPosts)
}
}
}
}Testing
import CacheStore
import XCTest
@testable import CacheStoreDemo
class CacheStoreDemoTests: XCTestCase {
func testExample_success() throws {
let store = TestStore(
initialValues: [
.url: URL(string: "https://jsonplaceholder.typicode.com/posts") as Any
],
actionHandler: actionHandler,
dependency: .mock
)
store.send(.fetchPosts) { cacheStore in
cacheStore.set(value: true, forKey: .isLoading)
}
store.send(.fetchPosts) { cacheStore in
cacheStore.set(value: true, forKey: .isLoading)
}
let expectedPosts: [Post] = [Post(id: 1, userId: 1, title: "Mock", body: "Post")]
store.receive(.postsResponse(.success(expectedPosts))) { cacheStore in
cacheStore.set(value: false, forKey: .isLoading)
cacheStore.set(value: expectedPosts, forKey: .posts)
}
}
func testExample_failure() throws {
let store = TestStore(
initialValues: [
:
],
actionHandler: actionHandler,
dependency: .mock
)
store.send(.fetchPosts, expecting: { _ in })
store.receive(.postsResponse(.failure("Key `.url` was not a URL"))) { cacheStore in
cacheStore.set(value: false, forKey: .isLoading)
}
}
}