Reset initialScrollOffset after the attracting animation ends

.circleci/config.yml

@@ -1,14 +1,43 @@
 version: 2.1
 
 jobs:
+  build-swift_5_7:
+    macos:
+      xcode: 13.4.1
+    steps:
+      - checkout
+      - run: xcodebuild -scheme FloatingPanel -workspace FloatingPanel.xcworkspace SWIFT_VERSION=5.7 clean build
+
+  build-swiftpm_ios15_7:
+    macos:
+      xcode: 13.4.1
+    steps:
+      - checkout
+      - run: swift build -Xswiftc "-sdk" -Xswiftc "`xcrun --sdk iphonesimulator --show-sdk-path`" -Xswiftc "-target" -Xswiftc "x86_64-apple-ios15.7-simulator"
+      - run: swift build -Xswiftc "-sdk" -Xswiftc "`xcrun --sdk iphonesimulator --show-sdk-path`" -Xswiftc "-target" -Xswiftc "arm64-apple-ios15.7-simulator"
+
+  test-ios15_5-iPhone_13_Pro:
+    macos:
+      xcode: 13.4.1
+    steps:
+      - checkout
+      - run: xcodebuild clean test -scheme FloatingPanel -workspace FloatingPanel.xcworkspace -destination 'platform=iOS Simulator,OS=15.5,name=iPhone 13 Pro'
   test-ios14_5-iPhone_12_Pro:
     macos:
       xcode: 13.4.1
     steps:
       - checkout
       - run: xcodebuild clean test -scheme FloatingPanel -workspace FloatingPanel.xcworkspace -destination 'platform=iOS Simulator,OS=14.5,name=iPhone 12 Pro'
 
+
 workflows:
   test: 
     jobs:
-      - test-ios14_5-iPhone_12_Pro
+      - build-swift_5_7:
+          name: build (5.7, 13.4.1)
+      - build-swiftpm_ios15_7:
+          name: swiftpm ({x86_64,arm64}-apple-ios15.5-simulator, 13.4.1)
+      - test-ios14_5-iPhone_12_Pro:
+          name: test (15.5, 13.4.1, iPhone 12 Pro)
+      - test-ios15_5-iPhone_13_Pro:
+          name: test (14.5, 13.4.1, iPhone 13 Pro)

.github/workflows/ci.yml

@@ -27,15 +27,6 @@ jobs:
           - swift: "5.8"
             xcode: "14.3.1"
             runs-on: macos-13
-          - swift: "5.7"
-            xcode: "14.1"
-            runs-on: macos-12
-          - swift: "5.6"
-            xcode: "13.4.1"
-            runs-on: macos-12
-          - swift: "5.5"
-            xcode: "13.2.1"
-            runs-on: macos-12
     steps:
       - uses: actions/checkout@v4
       - name: Building in Swift ${{ matrix.swift }}
@@ -59,11 +50,6 @@ jobs:
             sim: "iPhone 14 Pro"
             parallel: NO  # Stop random test job failures
             runs-on: macos-13
-          - os: "15.5"
-            xcode: "13.4.1"
-            sim: "iPhone 13 Pro"
-            parallel: NO  # Stop random test job failures
-            runs-on: macos-12
     steps:
     - uses: actions/checkout@v4
     - name: Testing in iOS ${{ matrix.os }}
@@ -137,13 +123,6 @@ jobs:
           - target: "arm64-apple-ios16.4-simulator"
             xcode: "14.3.1"
             runs-on: macos-13
-          # 15.7
-          - target: "x86_64-apple-ios15.7-simulator"
-            xcode: "14.1"
-            runs-on: macos-12
-          - target: "arm64-apple-ios15.7-simulator"
-            xcode: "14.1"
-            runs-on: macos-12
     steps:
     - uses: actions/checkout@v4
     - name: "Swift Package Manager build"

Sources/Core.swift

@@ -71,7 +71,7 @@ class Core: NSObject, UIGestureRecognizerDelegate {
     var removalVector: CGVector = .zero
 
     // Scroll handling
-    private var initialScrollOffset: CGPoint = .zero
+    private var initialScrollOffset: CGPoint?
     private var scrollBounce = false
     private var scrollIndictorVisible = false
     private var scrollBounceThreshold: CGFloat = -30.0
@@ -411,7 +411,7 @@ class Core: NSObject, UIGestureRecognizerDelegate {
 
             if insideMostExpandedAnchor {
                 // Prevent scrolling if needed
-                if isScrollable(state: state) {
+                if isScrollable(state: state), let initialScrollOffset = initialScrollOffset {
                     if interactionInProgress {
                         os_log(msg, log: devLog, type: .debug, "settle offset -- \(value(of: initialScrollOffset))")
                         // Return content offset to initial offset to prevent scrolling
@@ -429,7 +429,7 @@ class Core: NSObject, UIGestureRecognizerDelegate {
                             stopScrolling(at: initialScrollOffset)
                         }
                     }
-                } else {
+                } else if let initialScrollOffset = initialScrollOffset {
                     // Return content offset to initial offset to prevent scrolling
                     stopScrolling(at: initialScrollOffset)
                 }
@@ -471,7 +471,8 @@ class Core: NSObject, UIGestureRecognizerDelegate {
                     }
                     if isScrollable(state: state) {
                         // Adjust a small gap of the scroll offset just after swiping down starts in the grabber area.
-                        if surfaceView.grabberAreaContains(location), surfaceView.grabberAreaContains(initialLocation) {
+                        if surfaceView.grabberAreaContains(location), surfaceView.grabberAreaContains(initialLocation),
+                            let initialScrollOffset = initialScrollOffset {
                             stopScrolling(at: initialScrollOffset)
                         }
                     }
@@ -499,7 +500,8 @@ class Core: NSObject, UIGestureRecognizerDelegate {
                             }
                         }
                         // Adjust a small gap of the scroll offset just before swiping down starts in the grabber area,
-                        if surfaceView.grabberAreaContains(location), surfaceView.grabberAreaContains(initialLocation) {
+                        if surfaceView.grabberAreaContains(location), surfaceView.grabberAreaContains(initialLocation),
+                            let initialScrollOffset = initialScrollOffset {
                             stopScrolling(at: initialScrollOffset)
                         }
                     }
@@ -847,7 +849,7 @@ class Core: NSObject, UIGestureRecognizerDelegate {
             } else {
                 initialScrollOffset = scrollView.contentOffset
             }
-            os_log(msg, log: devLog, type: .debug, "initial scroll offset -- \(initialScrollOffset)")
+            os_log(msg, log: devLog, type: .debug, "initial scroll offset -- \(optional: initialScrollOffset)")
         }
 
         initialTranslation = translation
@@ -894,17 +896,6 @@ class Core: NSObject, UIGestureRecognizerDelegate {
         return true
     }
 
-    func endWithoutAttraction(_ target: FloatingPanelState) {
-        self.state = target
-        self.updateLayout(to: target)
-        self.unlockScrollView()
-        // The `floatingPanelDidEndDragging(_:willAttract:)` must be called after the state property changes.
-        // This allows library users to get the correct state in the delegate method.
-        if let vc = ownerVC {
-            vc.delegate?.floatingPanelDidEndDragging?(vc, willAttract: false)
-        }
-    }
-
     private func startAttraction(to state: FloatingPanelState, with velocity: CGPoint, completion: @escaping (() -> Void)) {
         os_log(msg, log: devLog, type: .debug, "startAnimation to \(state) -- velocity = \(value(of: velocity))")
         guard let vc = ownerVC else { return }
@@ -934,8 +925,8 @@ class Core: NSObject, UIGestureRecognizerDelegate {
                 self.backdropView.alpha = self.getBackdropAlpha(at: current, with: translation)
 
                 // Pin the offset of the tracking scroll view while moving by this animator
-                if let scrollView = self.scrollView {
-                    self.stopScrolling(at: self.initialScrollOffset)
+                if let scrollView = self.scrollView, let initialScrollOffset = self.initialScrollOffset {
+                    self.stopScrolling(at: initialScrollOffset)
                     os_log(msg, log: devLog, type: .debug, "move -- pinning scroll offset = \(scrollView.contentOffset)")
                 }
 
@@ -959,6 +950,12 @@ class Core: NSObject, UIGestureRecognizerDelegate {
         self.isAttracting = false
         self.moveAnimator = nil
 
+        // We need to reset `initialScrollOffset` because the scroll offset can become unexpected
+        // under the following circumstances:
+        // 1. The scroll offset changes while the panel does not move.
+        // 2. The panel is then moved using `move(to:animate:completion:)`.
+        self.initialScrollOffset = nil
+
         if let vc = ownerVC {
             vc.delegate?.floatingPanelDidEndAttracting?(vc)
         }
@@ -981,6 +978,20 @@ class Core: NSObject, UIGestureRecognizerDelegate {
         }
     }
 
+    func endWithoutAttraction(_ target: FloatingPanelState) {
+        // See comments in `endAttraction`
+        self.initialScrollOffset = nil
+
+        self.state = target
+        self.updateLayout(to: target)
+        self.unlockScrollView()
+        // The `floatingPanelDidEndDragging(_:willAttract:)` must be called after the state property changes.
+        // This allows library users to get the correct state in the delegate method.
+        if let vc = ownerVC {
+            vc.delegate?.floatingPanelDidEndDragging?(vc, willAttract: false)
+        }
+    }
+
     func value(of point: CGPoint) -> CGFloat {
         return layoutAdapter.position.mainLocation(point)
     }

Sources/Logging.swift

@@ -15,3 +15,14 @@ struct Logging {
     static let category = "FloatingPanel"
     private init() {}
 }
+
+extension String.StringInterpolation {
+    mutating func appendInterpolation<T>(optional: T?, defaultValue: String = "nil") {
+        switch optional {
+        case let value?:
+            appendLiteral(String(describing: value))
+        case nil:
+            appendLiteral(defaultValue)
+        }
+    }
+}

Tests/CoreTests.swift

@@ -916,6 +916,34 @@ class CoreTests: XCTestCase {
         }
     }
 
+    func test_initial_scroll_offset_reset() {
+        let fpc = FloatingPanelController()
+        let scrollView = UIScrollView()
+        fpc.layout = FloatingPanelBottomLayout()
+        fpc.track(scrollView: scrollView)
+        fpc.showForTest()
+
+        fpc.move(to: .full, animated: false)
+
+        fpc.panGestureRecognizer.state = .began
+        fpc.floatingPanel.handle(panGesture: fpc.panGestureRecognizer)
+
+        fpc.panGestureRecognizer.state = .cancelled
+        fpc.floatingPanel.handle(panGesture: fpc.panGestureRecognizer)
+
+        waitRunLoop(secs: 1.0)
+
+        let expect = CGPoint(x: 0, y: 100)
+
+        scrollView.setContentOffset(expect, animated: false)
+
+        fpc.move(to: .half, animated: true)
+
+        waitRunLoop(secs: 1.0)
+
+        XCTAssertEqual(expect, scrollView.contentOffset)
+    }
+
     func test_handleGesture_endWithoutAttraction() throws {
         class Delegate: FloatingPanelControllerDelegate {
             var willAttract: Bool?