improve onPreferenceChange closure MainActor handling

Package.swift

@@ -29,6 +29,7 @@ let package = Package(
     ],
     dependencies: [
         .package(url: "https://github.com/StanfordSpezi/Spezi.git", from: "1.8.0"),
+        .package(url: "https://github.com/StanfordSpezi/SpeziFoundation.git", from: "2.0.1"),
         .package(url: "https://github.com/apple/swift-collections.git", from: "1.1.0"),
         .package(url: "https://github.com/pointfreeco/swift-snapshot-testing.git", from: "1.17.0")
     ] + swiftLintPackage(),

Sources/SpeziValidation/ValidationState/ReceiveValidationModifier.swift

@@ -6,19 +6,10 @@
 // SPDX-License-Identifier: MIT
 //
 
+import SpeziFoundation
 import SwiftUI
 
 
-@MainActor
-private struct IsolatedValidationBinding: Sendable {
-    let state: ValidationState.Binding
-
-    init(_ state: ValidationState.Binding) {
-        self.state = state
-    }
-}
-
-
 /// Provide access to validation state to the parent view.
 ///
 /// The internal preference key to provide parent views access to all configured ``ValidationEngine`` and input
@@ -46,11 +37,9 @@ extension View {
     /// - Parameter state: The binding to the ``ValidationState``.
     /// - Returns: The modified view.
     public func receiveValidation(in state: ValidationState.Binding) -> some View {
-        let binding = IsolatedValidationBinding(state)
-
-        return onPreferenceChange(CapturedValidationStateKey.self) { entries in
-            Task { @Sendable @MainActor in
-                binding.state.wrappedValue = ValidationContext(entries: entries)
+        onPreferenceChange(CapturedValidationStateKey.self) { entries in
+            runOrScheduleOnMainActor {
+                state.wrappedValue = ValidationContext(entries: entries)
             }
         }
     }

Sources/SpeziValidation/ValidationState/ValidationContext.swift

@@ -17,7 +17,7 @@ import SwiftUI
 ///
 /// You can use this structure to retrieve the state of all ``ValidationEngine``s of a subview or manually
 /// initiate validation by calling ``validateSubviews(switchFocus:)``. E.g., when pressing on a submit button of a form.
-public struct ValidationContext {
+public struct ValidationContext: Sendable {
     private let entries: [CapturedValidationState]
 
 

Sources/SpeziValidation/ValidationState/ValidationState.swift

@@ -67,8 +67,8 @@ public struct ValidationState: DynamicProperty {
 extension ValidationState {
     /// A binding to a ``ValidationState``.
     @propertyWrapper
-    public struct Binding {
-        private let binding: SwiftUI.Binding<ValidationContext>
+    public struct Binding: Sendable {
+        @MainActor private let binding: SwiftUI.Binding<ValidationContext>
 
         /// The validation context.
         public var wrappedValue: ValidationContext {

Sources/SpeziViews/Views/Layout/HorizontalGeometryReader.swift

@@ -6,6 +6,7 @@
 // SPDX-License-Identifier: MIT
 //
 
+import SpeziFoundation
 import SwiftUI
 
 
@@ -39,18 +40,8 @@ public struct HorizontalGeometryReader<Content: View>: View {
                 }
             )
             .onPreferenceChange(WidthPreferenceKey.self) { width in
-                // The `onPreferenceChange` view modfier now takes a `@Sendable` closure, therefore we cannot capture `@MainActor` isolated properties
-                // on the `View` directly anymore: https://developer.apple.com/documentation/swiftui/view/onpreferencechange(_:perform:)?changes=latest_minor
-                // However, as the `@Sendable` closure is still run on the MainActor (at least in my testing on 18.2 RC SDKs), we can use `MainActor.assumeIsolated`
-                // to avoid scheduling a `MainActor` `Task`, which could delay execution and cause unexpected UI behavior.
-                if Thread.isMainThread {
-                    MainActor.assumeIsolated {
-                        self.width = width
-                    }
-                } else {
-                    Task { @MainActor in
-                        self.width = width
-                    }
+                runOrScheduleOnMainActor {
+                    self.width = width
                 }
             }
     }

Tests/SpeziViewsTests/SnapshotTests.swift

@@ -20,8 +20,7 @@ final class SnapshotTests: XCTestCase {
                 Text(verbatim: "20 °C, Sunny")
             }
         }
-
-
+
         let largeRow = row
             .dynamicTypeSize(.accessibility3)
 

Tests/UITests/TestApp/ViewsTests/CanvasTestView.swift

@@ -8,6 +8,7 @@
 
 #if canImport(PencilKit) && !os(macOS)
 import PencilKit
+import SpeziFoundation
 import SpeziViews
 import SwiftUI
 
@@ -47,15 +48,8 @@ struct CanvasTestView: View {
             }
             .navigationBarTitleDisplayMode(.inline)
             .onPreferenceChange(CanvasView.CanvasSizePreferenceKey.self) { size in
-                // See `HorizontalGeometryReader.swift`
-                if Thread.isMainThread {
-                    MainActor.assumeIsolated {
-                        self.receivedSize = size
-                    }
-                } else {
-                    Task { @MainActor in
-                        self.receivedSize = size
-                    }
+                runOrScheduleOnMainActor {
+                    self.receivedSize = size
                 }
             }
     }

Tests/UITests/TestAppUITests/SpeziViews/ViewsTests.swift

@@ -34,17 +34,17 @@
 
         #if os(visionOS)
         // visionOS doesn't have the image anymore, this should be enough to check
-        let paletteView = app.scrollViews.otherElements["Pen, black"]
+        let penView = app.scrollViews.otherElements["Pen, black"]
         #else
-        let paletteView = app.images["palette_tool_pencil_base"]
+        let penView = app.buttons["Pen"]
         #endif
 
 
         XCTAssert(app.collectionViews.buttons["Canvas"].waitForExistence(timeout: 2))
         app.collectionViews.buttons["Canvas"].tap()
 
         XCTAssert(app.staticTexts["Did Draw Anything: false"].waitForExistence(timeout: 2))
-        XCTAssertFalse(paletteView.exists)
+        XCTAssertFalse(penView.exists)
 
         let canvasView = app.scrollViews.firstMatch
         canvasView.swipeRight()
@@ -55,7 +55,7 @@
         XCTAssert(app.buttons["Show Tool Picker"].waitForExistence(timeout: 2))
         app.buttons["Show Tool Picker"].tap()
 
-        XCTAssertTrue(paletteView.waitForExistence(timeout: 5))
+        XCTAssertTrue(penView.waitForExistence(timeout: 5))
         canvasView.swipeLeft()
 
         XCTAssertTrue(canvasView.waitForExistence(timeout: 2.0))
@@ -65,12 +65,7 @@
         return // the pencilKit toolbar cannot be hidden anymore on visionOS
         #endif
 
-#if compiler(>=6)
-        XCTAssertTrue(paletteView.waitForNonExistence(timeout: 15))
-#else
-        sleep(15) // waitForExistence will otherwise return immediately
-        XCTAssertFalse(paletteView.exists)
-#endif
+        XCTAssertTrue(penView.waitForNonExistence(timeout: 15))
         canvasView.swipeUp()
     }