Split subscription logic.

ReactiveCocoa · May 28, 2020 · 2a29ae7 · 2a29ae7
1 parent e4d65d7
commit 2a29ae7
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Showing 6 changed files with 78 additions and 37 deletions.
diff --git a/Loop.xcodeproj/project.pbxproj b/Loop.xcodeproj/project.pbxproj
@@ -47,6 +47,9 @@
 		5B8F922124732C4600C1C90E /* SwiftUIBasicBindingHomeView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5B8F922024732C4600C1C90E /* SwiftUIBasicBindingHomeView.swift */; };
 		5B8F922324732C9500C1C90E /* LoopBindingExampleView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5B8F922224732C9500C1C90E /* LoopBindingExampleView.swift */; };
 		5B8F922724732E1700C1C90E /* SimpleCounterView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5B8F922624732E1700C1C90E /* SimpleCounterView.swift */; };
+		5BAB9750247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BAB974F247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift */; };
+		5BAB9751247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BAB974F247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift */; };
+		5BAB9752247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BAB974F247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift */; };
 		5BC88F842469CBA300394C63 /* Nimble.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 5BC88F832469CBA300394C63 /* Nimble.framework */; };
 		5BC88F862469CBAB00394C63 /* Nimble.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 5BC88F852469CBAB00394C63 /* Nimble.framework */; };
 		5BC88F88246AFC5900394C63 /* ReactiveSwift+EnqueueTo.swift in Sources */ = {isa = PBXBuildFile; fileRef = 5BC88F87246AFC5900394C63 /* ReactiveSwift+EnqueueTo.swift */; };
@@ -228,6 +231,7 @@
 		5B8F922224732C9500C1C90E /* LoopBindingExampleView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = LoopBindingExampleView.swift; sourceTree = "<group>"; };
 		5B8F922424732CA000C1C90E /* EnvironmentLoopExampleView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = EnvironmentLoopExampleView.swift; sourceTree = "<group>"; };
 		5B8F922624732E1700C1C90E /* SimpleCounterView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SimpleCounterView.swift; sourceTree = "<group>"; };
+		5BAB974F247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = SwiftUIHotSwappableSubscription.swift; sourceTree = "<group>"; };
 		5BC88F832469CBA300394C63 /* Nimble.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = Nimble.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		5BC88F852469CBAB00394C63 /* Nimble.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; path = Nimble.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		5BC88F87246AFC5900394C63 /* ReactiveSwift+EnqueueTo.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = "ReactiveSwift+EnqueueTo.swift"; sourceTree = "<group>"; };
@@ -468,6 +472,7 @@
 				5B8F92132473250E00C1C90E /* EnvironmentLoop.swift */,
 				5B8F921B247325C300C1C90E /* EnvironmentValues.swift */,
 				5B8F920F2473242900C1C90E /* SwiftUISubscription.swift */,
+				5BAB974F247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift */,
 			);
 			path = SwiftUI;
 			sourceTree = "<group>";
@@ -815,6 +820,7 @@
 				65761B2E23CF4CA2004D5506 /* NSLock+Extensions.swift in Sources */,
 				5BC88F9C246B1CDE00394C63 /* SignalProducer+Loop.swift in Sources */,
 				5BC88F92246B17B200394C63 /* Context.swift in Sources */,
+				5BAB9750247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift in Sources */,
 				585CD87B239E6A39004BE9CC /* Reducer.swift in Sources */,
 				9AD5D42D1F97375E00E6AE5A /* Property+System.swift in Sources */,
 				5BC88F88246AFC5900394C63 /* ReactiveSwift+EnqueueTo.swift in Sources */,
@@ -869,6 +875,7 @@
 				65761B2F23CF4CA2004D5506 /* NSLock+Extensions.swift in Sources */,
 				5BC88F9D246B1CDE00394C63 /* SignalProducer+Loop.swift in Sources */,
 				5BC88F93246B17B200394C63 /* Context.swift in Sources */,
+				5BAB9751247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift in Sources */,
 				585CD87C239E6A3E004BE9CC /* Reducer.swift in Sources */,
 				65F8C262218371A800924657 /* Property+System.swift in Sources */,
 				5BC88F89246AFC5900394C63 /* ReactiveSwift+EnqueueTo.swift in Sources */,
@@ -893,6 +900,7 @@
 				65761B3023CF4CA2004D5506 /* NSLock+Extensions.swift in Sources */,
 				5BC88F9E246B1CDE00394C63 /* SignalProducer+Loop.swift in Sources */,
 				5BC88F94246B17B200394C63 /* Context.swift in Sources */,
+				5BAB9752247FFBC10079B532 /* SwiftUIHotSwappableSubscription.swift in Sources */,
 				585CD87D239E6A3E004BE9CC /* Reducer.swift in Sources */,
 				65F8C271218371AC00924657 /* Property+System.swift in Sources */,
 				5BC88F8A246AFC5900394C63 /* ReactiveSwift+EnqueueTo.swift in Sources */,

diff --git a/Loop/Public/SwiftUI/EnvironmentLoop.swift b/Loop/Public/SwiftUI/EnvironmentLoop.swift
@@ -7,11 +7,11 @@ import ReactiveSwift
 @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
 @propertyWrapper
 public struct EnvironmentLoop<State, Event>: DynamicProperty {
-    @Environment(\.loops[ObjectIdentifier(Loop<State, Event>.self)])
-    var erasedLoop: Any?
+    @Environment(\.loops[LoopType(Loop<State, Event>.self)])
+    var erasedLoop: AnyObject?
 
     @ObservedObject
-    private var subscription: SwiftUISubscription<State, Event>
+    private var subscription: SwiftUIHotSwappableSubscription<State, Event>
 
     @inlinable
     public var wrappedValue: State {
@@ -30,23 +30,15 @@ public struct EnvironmentLoop<State, Event>: DynamicProperty {
     internal var acknowledgedState: State!
 
     public init() {
-        self.subscription = SwiftUISubscription()
+        self.subscription = SwiftUIHotSwappableSubscription()
     }
 
     public mutating func update() {
-        if isKnownUniquelyReferenced(&subscription) == false {
-            subscription = SwiftUISubscription()
-        }
-
-        if subscription.hasStarted == false {
-            guard let loop = erasedLoop as! Loop<State, Event>? else {
-                fatalError("Expect parent view to inject a `Loop<\(State.self), \(Event.self)>` through `View.environmentLoop(_:)`. Found none.")
-            }
-
-            subscription.attach(to: loop)
+        guard let loop = erasedLoop as! Loop<State, Event>? else {
+            fatalError("Expect parent view to inject a `Loop<\(State.self), \(Event.self)>` through `View.environmentLoop(_:)`. Found none.")
         }
 
-        acknowledgedState = subscription.latestValue
+        acknowledgedState = subscription.currentState(in: loop)
     }
 }
 

diff --git a/Loop/Public/SwiftUI/EnvironmentValues.swift b/Loop/Public/SwiftUI/EnvironmentValues.swift
@@ -6,7 +6,7 @@ import SwiftUI
 extension View {
     @inlinable
     public func environmentLoop<State, Event>(_ loop: Loop<State, Event>) -> some View {
-        let typeId = ObjectIdentifier(type(of: loop))
+        let typeId = LoopType(type(of: loop))
 
         return transformEnvironment(\.loops) { loops in
             loops[typeId] = loop
@@ -16,17 +16,28 @@ extension View {
 
 @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
 extension EnvironmentValues {
-    public var loops: [ObjectIdentifier: Any] {
+    @usableFromInline
+    internal var loops: [LoopType: AnyObject] {
         get { self[LoopEnvironmentKey.self] }
         set { self[LoopEnvironmentKey.self] = newValue }
     }
 }
 
 @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
 internal enum LoopEnvironmentKey: EnvironmentKey {
-    static var defaultValue: [ObjectIdentifier: Any] {
+    static var defaultValue: [LoopType: AnyObject] {
         return [:]
     }
 }
 
+@usableFromInline
+struct LoopType: Hashable {
+    let id: ObjectIdentifier
+
+    @usableFromInline
+    init(_ type: Any.Type) {
+        id = ObjectIdentifier(type)
+    }
+}
+
 #endif
diff --git a/Loop/Public/SwiftUI/LoopBinding.swift b/Loop/Public/SwiftUI/LoopBinding.swift
@@ -22,19 +22,19 @@ public struct LoopBinding<State, Event>: DynamicProperty {
     }
 
     @usableFromInline
-    internal var acknowledgedState: State!
+    internal var acknowledgedState: State
 
     public init(_ loop: Loop<State, Event>) {
         // The subscription can be copied without restrictions.
-        self.subscription = SwiftUISubscription()
+        let subscription = SwiftUISubscription(loop: loop)
+
+        self.subscription = subscription
+        self.acknowledgedState = subscription.latestValue
         self.loop = loop
     }
 
     public mutating func update() {
-        if subscription.hasStarted == false {
-            subscription.attach(to: loop)
-        }
-
+        // Move latest value from the subscription only when SwiftUI has requested an update.
         acknowledgedState = subscription.latestValue
     }
 

diff --git a/Loop/Public/SwiftUI/SwiftUIHotSwappableSubscription.swift b/Loop/Public/SwiftUI/SwiftUIHotSwappableSubscription.swift
@@ -0,0 +1,37 @@
+#if canImport(Combine)
+
+import Combine
+import ReactiveSwift
+
+@available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
+internal final class SwiftUIHotSwappableSubscription<State, Event>: ObservableObject {
+
+    @Published private var latestValue: State!
+    private weak var attachedLoop: Loop<State, Event>?
+    private var disposable: Disposable?
+
+    init() {}
+
+    deinit {
+        disposable?.dispose()
+    }
+
+    func currentState(in loop: Loop<State, Event>) -> State {
+        if attachedLoop !== loop {
+            disposable?.dispose()
+
+            latestValue = loop.box._current
+
+            disposable = loop.producer
+                .observe(on: UIScheduler())
+                .startWithValues { [weak self] state in
+                    guard let self = self else { return }
+                    self.latestValue = state
+                }
+        }
+
+        return latestValue
+    }
+}
+
+#endif
diff --git a/Loop/Public/SwiftUI/SwiftUISubscription.swift b/Loop/Public/SwiftUI/SwiftUISubscription.swift
@@ -1,26 +1,15 @@
-import SwiftUI
 #if canImport(Combine)
 
 import Combine
 import ReactiveSwift
 
 @available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
 internal final class SwiftUISubscription<State, Event>: ObservableObject {
-    @Published var latestValue: State!
-    private(set) var hasStarted = false
 
+    @Published var latestValue: State
     private var disposable: Disposable?
 
-    init() {}
-
-    deinit {
-        disposable?.dispose()
-    }
-
-    func attach(to loop: Loop<State, Event>) {
-        guard hasStarted == false else { return }
-        hasStarted = true
-
+    init(loop: Loop<State, Event>) {
         latestValue = loop.box._current
         disposable = loop.producer
             .observe(on: UIScheduler())
@@ -29,6 +18,10 @@ internal final class SwiftUISubscription<State, Event>: ObservableObject {
                 self.latestValue = state
             }
     }
+
+    deinit {
+        disposable?.dispose()
+    }
 }
 
 #endif