improve onPreferenceChange closure MainActor handling (#51)

# improve `onPreferenceChange` closure MainActor handling

## ♻️ Current situation & Problem
In response to Apple changing the `onPreferenceChange` API to no longer
MainActor-constrain its closure parameter,
#48 and
#50 updated all
`onPreferenceChange` calls to either schedule the change onto the
MainActor, or (in some cases) check if the closure is being called on
the MainActor, and then run it directly.

This PR fixes this, by using the `runOrScheduleOnMainActor` function
from SpeziFoundation


## ⚙️ Release Notes 
- Improve MainActor interactions in `onPreferenceChange` closures.


## 📚 Documentation
n/a


## ✅ Testing
There are no dedicated new tests but these changes do in fact fix tests
elsewhere.

## 📝 Code of Conduct & Contributing Guidelines 

By submitting creating this pull request, you agree to follow our [Code
of
Conduct](https://github.com/StanfordSpezi/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordSpezi/.github/blob/main/CONTRIBUTING.md):
- [x] I agree to follow the [Code of
Conduct](https://github.com/StanfordSpezi/.github/blob/main/CODE_OF_CONDUCT.md)
and [Contributing
Guidelines](https://github.com/StanfordSpezi/.github/blob/main/CONTRIBUTING.md).

---------

Co-authored-by: Andreas Bauer <[email protected]>

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 @@ final class ViewsTests: XCTestCase {
 
         #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 @@ final class ViewsTests: XCTestCase {
         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 @@ final class ViewsTests: XCTestCase {
         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()
     }