Bug on UIKit #2963
arnauddorgans
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Bug on UIKit
#2963
Replies: 5 comments
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Hi @arnauddorgans, when you say:
I'm not sure what you mean by "internal ID". What ID are you referring to? |
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Maybe some internal behavior with |
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Hi @arnauddorgans, what led you to believe that this is an issue with the "identity" of the store, or |
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@mbrandonw The fact that using an 
The complete code of the app is available under But I put it here with the print message where you can add the breakpoint to debug it (line 101) The full app code is available hereimport SwiftUI
import ComposableArchitecture
import Combine
@Reducer
struct Feature {
@ObservableState
struct State: Equatable {
let id: Int
var child: ChildFeature.State?
var isSelected: Bool = false
var isPending: Bool = false
}
enum Action {
case task
case selectionReceived(Int)
case pendingSelectionReceived(Set<Int>)
case child(ChildFeature.Action)
}
let child: ChildFeature
@Dependency(\.selectionClient) var selectionClient
var body: some Reducer<State, Action> {
Reduce { state, action in
switch action {
case .task:
return .run { send in
try await withThrowingTaskGroup(of: Void.self) { group in
group.addTask {
for await selection in selectionClient.selection.values {
await send(.selectionReceived(selection))
}
}
group.addTask {
for await selections in selectionClient.pendingSelection.values {
await send(.pendingSelectionReceived(selections))
}
}
try await group.waitForAll()
}
}
case let .selectionReceived(id):
let stateID = state.id
state.isSelected = id == stateID
return updateEffect(state: &state)
case let .pendingSelectionReceived(ids):
let stateID = state.id
state.isPending = ids.contains(stateID)
return updateEffect(state: &state)
case .child:
return .none
}
}
.ifLet(\.child, action: \.child) {
child
}
}
func updateEffect(state: inout State) -> Effect<Action> {
let isPending = state.isPending
let isSelected = state.isSelected
let shouldSelect = isPending || isSelected
if shouldSelect != (state.child != nil) {
state.child = shouldSelect ? .init(id: state.id) : nil
}
state.child?.isSelected = isSelected
state.child?.isPending = isPending
return .none
}
}
@Reducer
struct ChildFeature {
@ObservableState
struct State: Equatable {
let id: Int
var seconds: Int = 0
var isSelected: Bool = false
var isPending: Bool = false
}
enum Action {
case task
case timeReceived
}
var body: some Reducer<State, Action> {
Reduce { state, action in
switch action {
case .task:
return .run { [id = state.id] send in
await withTaskCancellationHandler(operation: {
for await _ in Timer.publish(every: 1, on: .main, in: .common).autoconnect().values {
await send(.timeReceived)
}
}, onCancel: {
if id == 0 {
print("CANCEL \(id)")
}
})
}
case .timeReceived:
state.seconds += 1
return .none
}
}
}
}
struct ContentView: View {
let store: StoreOf<Feature>
var body: some View {
ZStack {
if let childStore = store.scope(state: \.child, action: \.child) {
ChildView(store: childStore)
}
}
.task {
await store.send(.task).finish()
}
}
}
struct ChildView: View {
let store: StoreOf<ChildFeature>
var body: some View {
ZStack {
if store.isSelected {
Color.green
} else if store.isPending {
Color.yellow
}
Text(store.seconds, format: .number)
.font(.title)
}
.task {
await store.send(.task).finish()
}
}
}
struct SelectionClient: DependencyKey {
let selection: AnyPublisher<Int, Never>
let select: (Int) -> Void
let pendingSelection: AnyPublisher<Set<Int>, Never>
let setPendingSelection: (Set<Int>) -> Void
static let liveValue: SelectionClient = {
let subject = CurrentValueSubject<Int, Never>(0)
let pendingSelectionSubject = CurrentValueSubject<Set<Int>, Never>([])
return .init(
selection: subject.eraseToAnyPublisher(),
select: { subject.value = $0 },
pendingSelection: pendingSelectionSubject.eraseToAnyPublisher(),
setPendingSelection: { pendingSelectionSubject.value = $0 }
)
}()
}
extension DependencyValues {
var selectionClient: SelectionClient {
self[SelectionClient.self]
}
}
@main
struct TCABugApp: App {
@State var idSelected = false
var body: some Scene {
WindowGroup {
VStack {
Button(idSelected ? "ID" : "No ID") {
idSelected.toggle()
}
HostingView(idView: idSelected)
.id(idSelected)
}
}
}
}
struct HostingView: UIViewControllerRepresentable {
let idView: Bool
func makeUIViewController(context: Context) -> ViewController {
.init(idView: idView)
}
func updateUIViewController(_ uiViewController: ViewController, context: Context) { }
}
extension HostingView {
final class ViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
private let idView: Bool
@Dependency(\.selectionClient) private var selectionClient
private lazy var childControllers: [UIViewController] = [
childController(id: 0),
childController(id: 1),
childController(id: 2),
childController(id: 3)
]
init(idView: Bool) {
self.idView = idView
super.init(transitionStyle: .scroll, navigationOrientation: .vertical)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func viewDidLoad() {
super.viewDidLoad()
dataSource = self
delegate = self
selectionClient.select(0)
setViewControllers([childControllers[0]], direction: .forward, animated: false)
}
func childController(id: Int) -> UIViewController {
let view = childView(id: id)
return UIHostingController(rootView: view)
}
@ViewBuilder
func childView(id: Int) -> some View {
if idView {
let store = IDStoreOf<Feature>(initialState: .init(id: id)) {
Feature(child: .init())
}
IDStoreView(store: store) { store in
ContentView(store: store)
}
} else {
ContentView(store: .init(initialState: .init(id: id), reducer: {
Feature(child: .init())
}))
}
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let index = childControllers.firstIndex(of: viewController), childControllers.indices.contains(index - 1) else { return nil }
return childControllers[index - 1]
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let index = childControllers.firstIndex(of: viewController), childControllers.indices.contains(index + 1) else { return nil }
return childControllers[index + 1]
}
func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
selectionClient.setPendingSelection(Set(pendingViewControllers.compactMap {
childControllers.firstIndex(of: $0)
}))
}
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
if completed, let viewController = pageViewController.viewControllers?.last, let index = childControllers.firstIndex(of: viewController) {
selectionClient.select(index)
}
selectionClient.setPendingSelection([])
}
}
}
struct IDStoreView<ChildReducer, ChildView>: View where ChildView: View, ChildReducer: Reducer {
let store: StoreOf<IDReducer>
let content: (StoreOf<ChildReducer>) -> ChildView
init(
store idStore: IDStoreOf<ChildReducer>,
content: @escaping (StoreOf<ChildReducer>) -> ChildView
) {
let id = ChildID()
self.store = .init(
initialState: .init(idChild: .init(id: id, child: idStore.initialState)),
reducer: { IDReducer(child: idStore.reducer) }
)
self.content = content
}
var body: some View {
ForEach(store.scope(state: \.elements, action: \.elements), id: \.id) { store in
content(store.scope(state: \.child, action: \.child))
}
}
}
struct IDStoreOf<ChildReducer> where ChildReducer: Reducer {
let initialState: ChildReducer.State
let reducer: ChildReducer
init(
initialState: ChildReducer.State,
@ReducerBuilder<ChildReducer.State, ChildReducer.Action> reducer: () -> ChildReducer
) {
self.initialState = initialState
self.reducer = reducer()
}
init<BaseReducer>(
initialState: @autoclosure () -> ChildReducer.State,
@ReducerBuilder<ChildReducer.State, ChildReducer.Action> reducer: () -> ChildReducer,
withDependencies prepareDependencies: (inout DependencyValues) -> Void
) where ChildReducer == _DependencyKeyWritingReducer<BaseReducer> {
let (initialState, reducer, dependencies) = withDependencies(prepareDependencies) {
@Dependency(\.self) var dependencies
return (initialState(), reducer(), dependencies)
}
self.init(
initialState: initialState,
reducer: { reducer.dependency(\.self, dependencies) }
)
}
}
extension IDStoreView {
typealias ChildID = UUID
@Reducer
struct IDReducer {
@ObservableState
struct State {
var elements: IdentifiedArrayOf<IDChild.State>
init(idChild: IDChild.State) {
self.elements = .init(uniqueElements: [idChild])
}
}
enum Action {
case elements(IdentifiedActionOf<IDChild>)
}
let child: ChildReducer
var body: some Reducer<State, Action> {
Reduce { state, action in
switch action {
case .elements:
return .none
}
}
.forEach(\.elements, action: \.elements) {
IDChild(child: child)
}
}
}
}
extension IDStoreView.IDReducer {
@Reducer
struct IDChild {
@ObservableState
struct State: Identifiable {
var id: IDStoreView.ChildID
var child: ChildReducer.State
}
enum Action {
case child(ChildReducer.Action)
}
let child: ChildReducer
var body: some Reducer<State, Action> {
Scope(state: \.child, action: \.child) {
child
}
}
}
} |
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Hi @arnauddorgans, ok I see what is happening in your project now. While you do have multiple separate stores for each page, they are technically sharing the same cancellation ID. This is just how TCA is expected to operate today. Sometime soon there will be the idea of effects being quarantined to each store, but that just isn't how it works today. However, in my opinion it would be better to have a parent feature that encapsulates all of the pages of the controller and scope child stores from that feature rather than having 4 completely independent stores running your feature. Here is how you can do that: Full code:import SwiftUI
import ComposableArchitecture
import Combine
@Reducer
struct ParentFeature {
@ObservableState
struct State {
var features: IdentifiedArrayOf<Feature.State> = []
}
enum Action {
case features(IdentifiedActionOf<Feature>)
}
var body: some ReducerOf<Self> {
Reduce { state, action in
switch action {
case .features:
return .none
}
}
.forEach(\.features, action: \.features) {
Feature()
}
}
}
@Reducer
struct Feature {
@ObservableState
struct State: Equatable, Identifiable {
let id: Int
var child: ChildFeature.State?
var isSelected: Bool = false
var isPending: Bool = false
}
enum Action {
case task
case selectionReceived(Int)
case pendingSelectionReceived(Set<Int>)
case child(ChildFeature.Action)
}
@Dependency(\.selectionClient) var selectionClient
var body: some Reducer<State, Action> {
Reduce { state, action in
switch action {
case .task:
return .run { send in
try await withThrowingTaskGroup(of: Void.self) { group in
group.addTask {
for await selection in selectionClient.selection.values {
await send(.selectionReceived(selection))
}
}
group.addTask {
for await selections in selectionClient.pendingSelection.values {
await send(.pendingSelectionReceived(selections))
}
}
try await group.waitForAll()
}
}
case let .selectionReceived(id):
let stateID = state.id
state.isSelected = id == stateID
return updateEffect(state: &state)
case let .pendingSelectionReceived(ids):
let stateID = state.id
state.isPending = ids.contains(stateID)
return updateEffect(state: &state)
case .child:
return .none
}
}
.ifLet(\.child, action: \.child) {
ChildFeature()
}
}
func updateEffect(state: inout State) -> Effect<Action> {
let isPending = state.isPending
let isSelected = state.isSelected
let shouldSelect = isPending || isSelected
if shouldSelect != (state.child != nil) {
state.child = shouldSelect ? .init(id: state.id) : nil
}
state.child?.isSelected = isSelected
state.child?.isPending = isPending
return .none
}
}
@Reducer
struct ChildFeature {
@ObservableState
struct State: Equatable {
let id: Int
var seconds: Int = 0
var isSelected: Bool = false
var isPending: Bool = false
}
enum Action {
case task
case timeReceived
}
var body: some Reducer<State, Action> {
Reduce { state, action in
switch action {
case .task:
return .run { [id = state.id] send in
await withTaskCancellationHandler(operation: {
for await _ in Timer.publish(every: 1, on: .main, in: .common).autoconnect().values {
await send(.timeReceived)
}
}, onCancel: {
if id == 0 {
print("CANCEL \(id)")
}
})
}
case .timeReceived:
state.seconds += 1
return .none
}
}
}
}
struct ContentView: View {
let store: StoreOf<Feature>
var body: some View {
ZStack {
if let childStore = store.scope(state: \.child, action: \.child) {
ChildView(store: childStore)
}
}
.task {
await store.send(.task).finish()
}
}
}
struct ChildView: View {
let store: StoreOf<ChildFeature>
var body: some View {
ZStack {
if store.isSelected {
Color.green
} else if store.isPending {
Color.yellow
}
Text(store.seconds, format: .number)
.font(.title)
}
.task {
await store.send(.task).finish()
}
}
}
struct SelectionClient: DependencyKey {
let selection: AnyPublisher<Int, Never>
let select: (Int) -> Void
let pendingSelection: AnyPublisher<Set<Int>, Never>
let setPendingSelection: (Set<Int>) -> Void
static let liveValue: SelectionClient = {
let subject = CurrentValueSubject<Int, Never>(0)
let pendingSelectionSubject = CurrentValueSubject<Set<Int>, Never>([])
return .init(
selection: subject.eraseToAnyPublisher(),
select: { subject.value = $0 },
pendingSelection: pendingSelectionSubject.eraseToAnyPublisher(),
setPendingSelection: { pendingSelectionSubject.value = $0 }
)
}()
}
extension DependencyValues {
var selectionClient: SelectionClient {
self[SelectionClient.self]
}
}
@main
struct TCABugApp: App {
@State var idSelected = false
var body: some Scene {
WindowGroup {
HostingView()
}
}
}
struct HostingView: UIViewControllerRepresentable {
func makeUIViewController(context: Context) -> ViewController {
.init()
}
func updateUIViewController(_ uiViewController: ViewController, context: Context) { }
}
extension HostingView {
final class ViewController: UIPageViewController, UIPageViewControllerDataSource, UIPageViewControllerDelegate {
@Dependency(\.selectionClient) private var selectionClient
let store = Store(
initialState: ParentFeature.State(
features: [
Feature.State(id: 0),
Feature.State(id: 1),
Feature.State(id: 2),
Feature.State(id: 3),
]
)
) {
ParentFeature()
}
private var featureControllers: [UIViewController] = []
init() {
super.init(transitionStyle: .scroll, navigationOrientation: .vertical)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func viewDidLoad() {
super.viewDidLoad()
dataSource = self
delegate = self
observe { [weak self] in
guard let self else { return }
featureControllers = store.features.ids.map { id in
UIHostingController(
rootView: ContentView(
store: self.store.scope(
state: \.features[id: id]!,
action: \.features[id: id]
)
)
)
}
}
selectionClient.select(0)
setViewControllers([featureControllers[0]], direction: .forward, animated: false)
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerBefore viewController: UIViewController) -> UIViewController? {
guard let index = featureControllers.firstIndex(of: viewController), featureControllers.indices.contains(index - 1) else { return nil }
return featureControllers[index - 1]
}
func pageViewController(_ pageViewController: UIPageViewController, viewControllerAfter viewController: UIViewController) -> UIViewController? {
guard let index = featureControllers.firstIndex(of: viewController), featureControllers.indices.contains(index + 1) else { return nil }
return featureControllers[index + 1]
}
func pageViewController(_ pageViewController: UIPageViewController, willTransitionTo pendingViewControllers: [UIViewController]) {
selectionClient.setPendingSelection(Set(pendingViewControllers.compactMap {
featureControllers.firstIndex(of: $0)
}))
}
func pageViewController(_ pageViewController: UIPageViewController, didFinishAnimating finished: Bool, previousViewControllers: [UIViewController], transitionCompleted completed: Bool) {
if completed, let viewController = pageViewController.viewControllers?.last, let index = featureControllers.firstIndex(of: viewController) {
selectionClient.select(index)
}
selectionClient.setPendingSelection([])
}
}
}Putting in a little bit of upfront work to model the domains correctly comes with a lot of benefits. Since this isn't an issue with the library I am going to convert it to a discussion and feel free to continue the conversation over there. |
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Description
I found a bug when using multiple stores inside a
UIPageViewController.I made a demo app to reproduce the bug.
Basically, we have a
UIPageViewControllerthat contains 4 stores, each store is updated from a dependency and should display information about the current page's selection.When a page is selected, we increment a counter, and the background should be green; when the page is pending, the background should be yellow, and the counter should keep going.
Simulator.Screen.Recording.-.iPhone.15.-.2024-03-28.at.02.16.12.mp4
In the first part of the video, when the header button is "No ID," you will see that the first page's counter stops after the gesture is canceled.
This is because the
taskis canceled on the second page but should not be canceled on the first page.As far as I understand, the issue may come from multiple stores having the same internal IDs.
In the second part of the video, when the header button is "ID," you will see that everything is working as expected.
To workaround the issue, I created a store with
IdentifiedArrayOfwith a single item, and it seems to fix the bug because now each store has a different ID.Maybe it would be great to allow "detached" store creation to avoid this kind of issue.
The full app code is available here
Checklist
mainbranch of this package.The Composable Architecture version information
1.9.2
Destination operating system
iOS 17
Xcode version information
Xcode 15.3
Swift Compiler version information
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