Simplify Reusable Download Component (#756)

Author: stephencelis

Examples/CaseStudies/SwiftUICaseStudies/04-HigherOrderReducers-ResuableOfflineDownloads/DownloadClient.swift

@@ -3,8 +3,7 @@ import ComposableArchitecture
 import Foundation
 
 struct DownloadClient {
-  var cancel: (AnyHashable) -> Effect<Never, Never>
-  var download: (AnyHashable, URL) -> Effect<Action, Error>
+  var download: (URL) -> Effect<Action, Error>
 
   struct Error: Swift.Error, Equatable {}
 
@@ -16,14 +15,7 @@ struct DownloadClient {
 
 extension DownloadClient {
   static let live = DownloadClient(
-    cancel: { id in
-      .fireAndForget {
-        dependencies[id]?.observation.invalidate()
-        dependencies[id]?.task.cancel()
-        dependencies[id] = nil
-      }
-    },
-    download: { id, url in
+    download: { url in
       .run { subscriber in
         let task = URLSession.shared.dataTask(with: url) { data, _, error in
           switch (data, error) {
@@ -41,26 +33,13 @@ extension DownloadClient {
           subscriber.send(.updateProgress(progress.fractionCompleted))
         }
 
-        dependencies[id] = Dependencies(
-          observation: observation,
-          task: task
-        )
-
         task.resume()
 
         return AnyCancellable {
           observation.invalidate()
           task.cancel()
-          dependencies[id] = nil
         }
       }
     }
   )
 }
-
-private struct Dependencies {
-  let observation: NSKeyValueObservation
-  let task: URLSessionDataTask
-}
-
-private var dependencies: [AnyHashable: Dependencies] = [:]

Examples/CaseStudies/SwiftUICaseStudies/04-HigherOrderReducers-ResuableOfflineDownloads/DownloadComponent.swift

@@ -60,8 +60,7 @@ extension Reducer {
         case .alert(.cancelButtonTapped):
           state.mode = .notDownloaded
           state.alert = nil
-          return environment.downloadClient.cancel(state.id)
-            .fireAndForget()
+          return .cancel(id: state.id)
 
         case .alert(.deleteButtonTapped):
           state.alert = nil
@@ -86,9 +85,10 @@ extension Reducer {
           case .notDownloaded:
             state.mode = .startingToDownload
             return environment.downloadClient
-              .download(state.id, state.url)
+              .download(state.url)
               .throttle(for: 1, scheduler: environment.mainQueue, latest: true)
               .catchToEffect(DownloadComponentAction.downloadClient)
+              .cancellable(id: state.id)
 
           case .startingToDownload:
             state.alert = cancelAlert

Examples/CaseStudies/SwiftUICaseStudiesTests/04-HigherOrderReducers-ReusableOfflineDownloadsTests.swift

@@ -19,7 +19,7 @@ class ReusableComponentsDownloadComponentTests: XCTestCase {
 
   func testDownloadFlow() {
     var downloadClient = DownloadClient.failing
-    downloadClient.download = { _, _ in self.downloadSubject.eraseToEffect() }
+    downloadClient.download = { _ in self.downloadSubject.eraseToEffect() }
 
     let store = TestStore(
       initialState: DownloadComponentState(
@@ -54,7 +54,7 @@ class ReusableComponentsDownloadComponentTests: XCTestCase {
 
   func testDownloadThrottling() {
     var downloadClient = DownloadClient.failing
-    downloadClient.download = { _, _ in self.downloadSubject.eraseToEffect() }
+    downloadClient.download = { _ in self.downloadSubject.eraseToEffect() }
 
     let store = TestStore(
       initialState: DownloadComponentState(
@@ -94,10 +94,7 @@ class ReusableComponentsDownloadComponentTests: XCTestCase {
 
   func testCancelDownloadFlow() {
     var downloadClient = DownloadClient.failing
-    downloadClient.cancel = { _ in
-      .fireAndForget { self.downloadSubject.send(completion: .finished) }
-    }
-    downloadClient.download = { _, _ in self.downloadSubject.eraseToEffect() }
+    downloadClient.download = { _ in self.downloadSubject.eraseToEffect() }
 
     let store = TestStore(
       initialState: DownloadComponentState(
@@ -134,10 +131,7 @@ class ReusableComponentsDownloadComponentTests: XCTestCase {
 
   func testDownloadFinishesWhileTryingToCancel() {
     var downloadClient = DownloadClient.failing
-    downloadClient.cancel = { _ in
-      .fireAndForget { self.downloadSubject.send(completion: .finished) }
-    }
-    downloadClient.download = { _, _ in self.downloadSubject.eraseToEffect() }
+    downloadClient.download = { _ in self.downloadSubject.eraseToEffect() }
 
     let store = TestStore(
       initialState: DownloadComponentState(
@@ -175,10 +169,7 @@ class ReusableComponentsDownloadComponentTests: XCTestCase {
 
   func testDeleteDownloadFlow() {
     var downloadClient = DownloadClient.failing
-    downloadClient.cancel = { _ in
-      .fireAndForget { self.downloadSubject.send(completion: .finished) }
-    }
-    downloadClient.download = { _, _ in self.downloadSubject.eraseToEffect() }
+    downloadClient.download = { _ in self.downloadSubject.eraseToEffect() }
 
     let store = TestStore(
       initialState: DownloadComponentState(
@@ -210,7 +201,6 @@ class ReusableComponentsDownloadComponentTests: XCTestCase {
 
 extension DownloadClient {
   static let failing = Self(
-    cancel: { _ in .failing("DownloadClient.cancel") },
-    download: { _, _ in .failing("DownloadClient.download") }
+    download: { _ in .failing("DownloadClient.download") }
   )
 }