Fix target content offset edge case for small content (#120)

airbnb · Feb 21, 2024 · bfc6077 · bfc6077
1 parent d7bb3ff
commit bfc6077
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Showing 2 changed files with 42 additions and 3 deletions.
diff --git a/MagazineLayout/LayoutCore/Types/TargetContentOffsetAnchor.swift b/MagazineLayout/LayoutCore/Types/TargetContentOffsetAnchor.swift
@@ -40,10 +40,19 @@ enum TargetContentOffsetAnchor: Equatable {
   {
     let top = (-topInset).alignedToPixel(forScreenWithScale: scale)
     let bottom = (contentHeight + bottomInset - bounds.height).alignedToPixel(forScreenWithScale: scale)
+    let isAtTop = bounds.minY <= top
+    let isAtBottom = bounds.minY >= bottom
     let position: Position
-    if bounds.minY <= top {
+    if isAtTop, isAtBottom {
+      switch verticalLayoutDirection {
+      case .topToBottom: 
+        position = .atTop
+      case .bottomToTop: 
+        position = .atBottom
+      }
+    } else if isAtTop {
       position = .atTop
-    } else if bounds.minY >= bottom {
+    } else if isAtBottom {
       position = .atBottom
     } else {
       position = .inMiddle

diff --git a/Tests/TargetContentOffsetAnchorTests.swift b/Tests/TargetContentOffsetAnchorTests.swift
@@ -66,6 +66,21 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
     XCTAssert(anchor == .topItem(id: "6", itemEdge: .top, distanceFromTop: 20))
   }
 
+  func testAnchor_TopToBottom_SmallContentHeight() throws {
+    let anchor = TargetContentOffsetAnchor.targetContentOffsetAnchor(
+      verticalLayoutDirection: .topToBottom,
+      topInset: 50,
+      bottomInset: 30,
+      bounds: CGRect(x: 0, y: -50, width: 300, height: 400),
+      contentHeight: 50,
+      scale: 1,
+      firstVisibleItemID: "0",
+      lastVisibleItemID: "1",
+      firstVisibleItemFrame: CGRect(x: 0, y: 0, width: 300, height: 20),
+      lastVisibleItemFrame: CGRect(x: 0, y: 30, width: 300, height: 20))
+    XCTAssert(anchor == .top)
+  }
+
   // MARK: Bottom-to-Top Anchor Tests
 
   func testAnchor_BottomToTop_ScrolledToTop() throws {
@@ -113,7 +128,22 @@ final class TargetContentOffsetAnchorTests: XCTestCase {
     XCTAssert(anchor == .bottom)
   }
 
-  // MARK: To-to-Bottom Target Content Offset Tests
+  func testAnchor_BottomToTop_SmallContentHeight() throws {
+    let anchor = TargetContentOffsetAnchor.targetContentOffsetAnchor(
+      verticalLayoutDirection: .bottomToTop,
+      topInset: 50,
+      bottomInset: 30,
+      bounds: CGRect(x: 0, y: -50, width: 300, height: 400),
+      contentHeight: 50,
+      scale: 1,
+      firstVisibleItemID: "0",
+      lastVisibleItemID: "1",
+      firstVisibleItemFrame: CGRect(x: 0, y: 0, width: 300, height: 20),
+      lastVisibleItemFrame: CGRect(x: 0, y: 30, width: 300, height: 20))
+    XCTAssert(anchor == .bottom)
+  }
+
+  // MARK: Top-to-Bottom Target Content Offset Tests
 
   func testOffset_TopToBottom_ScrolledToTop() {
     let anchor = TargetContentOffsetAnchor.top