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MBL-1016: Create Paginator for pagination in Combine, plus Pagination…
…ExampleView for example usage
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Kickstarter-iOS/Features/PaginationExample/PaginationExampleView.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,82 @@ | ||
| import KsApi | ||
| import SwiftUI | ||
|
|
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| private struct PaginationExampleProjectCell: View { | ||
| let title: String | ||
| var body: some View { | ||
| Text(title) | ||
| .padding(.all, 10) | ||
| } | ||
| } | ||
|
|
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| private struct PaginationExampleProjectList: View { | ||
| @Binding var projectIdsAndTitles: [(Int, String)] | ||
| @Binding var showProgressView: Bool | ||
| @Binding var statusText: String | ||
|
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| let onRefresh: @Sendable() -> Void | ||
| let onDidShowProgressView: @Sendable() -> Void | ||
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| var body: some View { | ||
| HStack { | ||
| Spacer() | ||
| Text("👉 \(statusText)") | ||
| Spacer() | ||
| } | ||
| .padding(EdgeInsets(top: 20, leading: 0, bottom: 20, trailing: 0)) | ||
| .background(Color.yellow) | ||
| List { | ||
| ForEach(projectIdsAndTitles, id: \.0) { | ||
| let title = $0.1 | ||
| PaginationExampleProjectCell(title: $0.1) | ||
| } | ||
| if showProgressView { | ||
| HStack { | ||
| Spacer() | ||
| Text("Loading 😉") | ||
| .onAppear { | ||
| onDidShowProgressView() | ||
| } | ||
| Spacer() | ||
| } | ||
| .background(Color.yellow) | ||
| } | ||
| } | ||
| .refreshable { | ||
| onRefresh() | ||
| } | ||
| } | ||
| } | ||
|
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| public struct PaginationExampleView: View { | ||
| @StateObject private var viewModel = PaginationExampleViewModel() | ||
|
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| public var body: some View { | ||
| let capturedViewModel = viewModel | ||
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| PaginationExampleProjectList( | ||
| projectIdsAndTitles: $viewModel.projectIdsAndTitles, | ||
| showProgressView: $viewModel.showProgressView, | ||
| statusText: $viewModel.statusText, | ||
| onRefresh: { | ||
| capturedViewModel.didRefresh() | ||
| }, | ||
| onDidShowProgressView: { | ||
| capturedViewModel.didShowProgressView() | ||
| } | ||
| ) | ||
| } | ||
| } | ||
|
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| #Preview { | ||
| PaginationExampleProjectList( | ||
| projectIdsAndTitles: .constant([ | ||
| (1, "Cool project one"), | ||
| (2, "Cool project two"), | ||
| (3, "Cool project three") | ||
| ]), | ||
| showProgressView: .constant(true), | ||
| statusText: .constant("Example status text"), | ||
| onRefresh: {}, onDidShowProgressView: {} | ||
| ) | ||
| } |
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Kickstarter-iOS/Features/PaginationExample/PaginationExampleViewModel.swift
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,85 @@ | ||
| import Combine | ||
| import Foundation | ||
| import KsApi | ||
| import Library | ||
|
|
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| extension Project: Identifiable {} | ||
|
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| internal class PaginationExampleViewModel: ObservableObject { | ||
| var paginator: Paginator<DiscoveryEnvelope, Project, String, ErrorEnvelope, DiscoveryParams> | ||
|
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| @Published var projectIdsAndTitles: [(Int, String)] = [] | ||
| @Published var showProgressView: Bool = true | ||
| @Published var statusText: String = "" | ||
|
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| init() { | ||
| self.paginator = Paginator( | ||
| valuesFromEnvelope: { | ||
| $0.projects | ||
| }, | ||
| cursorFromEnvelope: { | ||
| $0.urls.api.moreProjects | ||
| }, | ||
| requestFromParams: { | ||
| AppEnvironment.current.apiService.fetchDiscovery_combine(params: $0) | ||
| }, | ||
| requestFromCursor: { | ||
| AppEnvironment.current.apiService.fetchDiscovery_combine(paginationUrl: $0) | ||
| } | ||
| ) | ||
|
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| self.paginator.$values.map { projects in | ||
| projects.map { ($0.id, $0.name) } | ||
| }.assign(to: &$projectIdsAndTitles) | ||
|
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| let canLoadMore = self.paginator.$state.map { state in | ||
| state == .someLoaded || state == .unloaded | ||
| } | ||
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| Publishers.CombineLatest(self.paginator.$isLoading, canLoadMore) | ||
| .map { isLoading, canLoadMore in | ||
| isLoading || canLoadMore | ||
| }.assign(to: &$showProgressView) | ||
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| self.paginator.$state.map { [weak self] state in | ||
| switch state { | ||
| case .error: | ||
| let errorText = self?.paginator.error?.errorMessages.first ?? "Unknown error" | ||
| return "Error: \(errorText)" | ||
| case .unloaded: | ||
| return "Waiting to load" | ||
| case .someLoaded: | ||
| let count = self?.paginator.values.count ?? 0 | ||
| return "Got \(count) results; more are available" | ||
| case .allLoaded: | ||
| return "Loaded all results" | ||
| case .empty: | ||
| return "No results" | ||
| } | ||
| } | ||
| .assign(to: &$statusText) | ||
| } | ||
|
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| var searchParams: DiscoveryParams { | ||
| var params = DiscoveryParams.defaults | ||
| params.staffPicks = true | ||
| params.sort = .magic | ||
| return params | ||
| } | ||
|
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| func didShowProgressView() { | ||
| if self.paginator.isLoading { | ||
| return | ||
| } | ||
|
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| if self.paginator.state == .someLoaded { | ||
| self.paginator.requestNextPage() | ||
| } else if self.paginator.state == .unloaded { | ||
| self.paginator.requestFirstPage(withParams: self.searchParams) | ||
| } | ||
| } | ||
|
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| func didRefresh() { | ||
| self.paginator.requestFirstPage(withParams: self.searchParams) | ||
| } | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,136 @@ | ||
| import Combine | ||
| import Foundation | ||
|
|
||
| /** | ||
| Used to coordinate the process of paginating through values. This class is specific to the type of pagination | ||
| in which a page's results contains a cursor that can be used to request the next page of values. | ||
| This class is designed to work with SwiftUI/Combine. For an example, see `PaginationExampleView.swift`. | ||
| This class is generic over the following types: | ||
| * `Value`: The type of value that is being paginated, i.e. a single row, not the array of rows. The | ||
| value must be equatable. | ||
| * `Envelope`: The type of response we get from fetching a new page of values. | ||
| * `SomeError`: The type of error we might get from fetching a new page of values. | ||
| * `Cursor`: The type of value that can be extracted from `Envelope` to request the next page of | ||
| values. | ||
| * `RequestParams`: The type that allows us to make a request for values without a cursor. | ||
| - parameter valuesFromEnvelope: A function to get an array of values from the results envelope. | ||
| - parameter cursorFromEnvelope: A function to get the cursor for the next page from a results envelope. | ||
| - parameter requestFromParams: A function to get a request for values from a params value. | ||
| - parameter requestFromCursor: A function to get a request for values from a cursor value. | ||
| You can observe the results of `values`, `isLoading`, `error` and `state` to access the loaded data. | ||
| */ | ||
|
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| public class Paginator<Envelope, Value: Equatable, Cursor, SomeError: Error, RequestParams> { | ||
| public enum Results: Equatable { | ||
| case unloaded | ||
| case someLoaded | ||
| case allLoaded | ||
| case empty | ||
| case error | ||
| } | ||
|
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| @Published public var values: [Value] | ||
| @Published public var isLoading: Bool | ||
| @Published public var error: SomeError? | ||
| @Published public var state: Results | ||
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| private var valuesFromEnvelope: (Envelope) -> [Value] | ||
| private var cursorFromEnvelope: (Envelope) -> Cursor? | ||
| private var requestFromParams: (RequestParams) -> AnyPublisher<Envelope, SomeError> | ||
| private var requestFromCursor: (Cursor) -> AnyPublisher<Envelope, SomeError> | ||
| private var cancellables = Set<AnyCancellable>() | ||
|
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| private var lastCursor: Cursor? | ||
|
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| public init(valuesFromEnvelope: @escaping ((Envelope) -> [Value]), | ||
| cursorFromEnvelope: @escaping ((Envelope) -> Cursor?), | ||
| requestFromParams: @escaping ((RequestParams) -> AnyPublisher<Envelope, SomeError>), | ||
| requestFromCursor: @escaping ((Cursor) -> AnyPublisher<Envelope, SomeError>)) { | ||
| self.values = [] | ||
| self.isLoading = false | ||
| self.error = nil | ||
| self.state = .unloaded | ||
|
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| self.valuesFromEnvelope = valuesFromEnvelope | ||
| self.cursorFromEnvelope = cursorFromEnvelope | ||
| self.requestFromParams = requestFromParams | ||
| self.requestFromCursor = requestFromCursor | ||
| } | ||
|
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| func handleRequest(_ request: AnyPublisher<Envelope, SomeError>) { | ||
| request | ||
| .receive(on: RunLoop.main) | ||
| .catch { [weak self] error -> AnyPublisher<Envelope, SomeError> in | ||
| self?.error = error | ||
| self?.state = .error | ||
| return Empty<Envelope, SomeError>().eraseToAnyPublisher() | ||
| } | ||
| .assertNoFailure() | ||
| .handleEvents(receiveCompletion: { [weak self] _ in | ||
| self?.isLoading = false | ||
| }, receiveCancel: { [weak self] in | ||
| self?.isLoading = false | ||
| }) | ||
| .sink(receiveValue: { [weak self] envelope in | ||
| guard let self = self else { | ||
| return | ||
| } | ||
|
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| let newValues = self.valuesFromEnvelope(envelope) | ||
| self.values.append(contentsOf: newValues) | ||
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| let cursor = self.cursorFromEnvelope(envelope) | ||
| self.lastCursor = cursor | ||
|
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| if self.values.count == 0 { | ||
| self.state = .empty | ||
| } else if cursor == nil || newValues.count == 0 { | ||
| self.state = .allLoaded | ||
| } else { | ||
| self.state = .someLoaded | ||
| } | ||
| }) | ||
| .store(in: &self.cancellables) | ||
| } | ||
|
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| public func requestFirstPage(withParams params: RequestParams) { | ||
| self.cancel() | ||
|
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| self.values = [] | ||
| self.isLoading = true | ||
| self.error = nil | ||
|
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| let request = self.requestFromParams(params) | ||
| self.handleRequest(request) | ||
| } | ||
|
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| public func requestNextPage() { | ||
| if self.isLoading { | ||
| return | ||
| } | ||
|
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| if self.state != .someLoaded { | ||
| return | ||
| } | ||
|
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| self.isLoading = true | ||
| guard let cursor = self.lastCursor else { | ||
| assert(false, "Requested next page, but there is no cursor.") | ||
| } | ||
|
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| let request = self.requestFromCursor(cursor) | ||
| self.handleRequest(request) | ||
| } | ||
|
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| public func cancel() { | ||
| self.cancellables.forEach { cancellable in | ||
| cancellable.cancel() | ||
| } | ||
| } | ||
| } |
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