Merge pull request #101 from square/entin/distribution-rtl

Fix horizontal distribution in RTL layout

Example/ParalayoutSnapshotTests/ViewDistributionSnapshotTests.swift

@@ -104,6 +104,21 @@ final class ViewDistributionSnapshotTests: SnapshotTestCase {
         assertSnapshot(matching: containerView, as: .image, named: nameForSnapshot(with: []))
     }
 
+    func testHorizontalDistributionFollowsLayoutDirection() {
+        let view = HorizontalDistributionView(frame: CGRect(x: 0, y: 0, width: 160, height: 60))
+
+        assertSnapshot(
+            matching: view,
+            as: .image,
+            named: nameForSnapshot(with: ["LTR"])
+        )
+        assertSnapshot(
+            matching: view,
+            as: .image(traits: .init(layoutDirection: .rightToLeft)),
+            named: nameForSnapshot(with: ["RTL"])
+        )
+    }
+
 }
 
 // MARK: -
@@ -137,3 +152,63 @@ extension UIUserInterfaceLayoutDirection {
     }
 
 }
+
+// MARK: -
+
+final class HorizontalDistributionView: UIView {
+
+    // MARK: - Life Cycle
+
+    override init(frame: CGRect) {
+        super.init(frame: frame)
+
+        firstView.bounds.size = .init(width: 40, height: 40)
+        firstView.backgroundColor = .red
+        addSubview(firstView)
+
+        secondView.bounds.size = .init(width: 40, height: 40)
+        secondView.backgroundColor = .green
+        addSubview(secondView)
+
+        thirdView.bounds.size = .init(width: 40, height: 40)
+        thirdView.backgroundColor = .blue
+        addSubview(thirdView)
+
+        // Set arbitrary semantic content attributes to ensure the layout relies on the _receiver's_ effective layout
+        // direction, not that of the distributed views.
+        firstView.semanticContentAttribute = .forceLeftToRight
+        secondView.semanticContentAttribute = .forceRightToLeft
+
+        backgroundColor = .white
+    }
+
+    @available(*, unavailable)
+    required init?(coder: NSCoder) {
+        fatalError("init(coder:) has not been implemented")
+    }
+
+    // MARK: - Private Properties
+
+    private let firstView: UIView = .init()
+
+    private let secondView: UIView = .init()
+
+    private let thirdView: UIView = .init()
+
+    // MARK: - UIView
+
+    override func layoutSubviews() {
+        applyHorizontalSubviewDistribution(
+            [
+                1.flexible,
+                firstView,
+                1.flexible,
+                secondView,
+                1.flexible,
+                thirdView,
+                1.flexible,
+            ]
+        )
+    }
+
+}

Paralayout/UIView+Distribution.swift

@@ -254,17 +254,21 @@ extension UIView {
         let receiverLayoutDirection = effectiveUserInterfaceLayoutDirection
 
         // Okay, ready to go!
-        var viewOrigin = axis.leadingEdge(of: layoutBounds, layoutDirection: receiverLayoutDirection)
+        var leadingEdgePosition = axis.leadingEdge(of: layoutBounds, layoutDirection: receiverLayoutDirection)
         for item in items {
             switch item {
             case .view(let subview, let insets):
                 var frame = subview.untransformedFrame
 
-                switch axis {
-                case .horizontal:
-                    frame.origin.x = (viewOrigin - insets.left).roundedToPixel(in: self)
-                case .vertical:
-                    frame.origin.y = (viewOrigin - insets.top).roundedToPixel(in: self)
+                switch (axis, receiverLayoutDirection) {
+                case (.horizontal, .leftToRight):
+                    frame.origin.x = (leadingEdgePosition - insets.left).roundedToPixel(in: self)
+                case (.horizontal, .rightToLeft):
+                    frame.origin.x = (leadingEdgePosition + insets.right - frame.width).roundedToPixel(in: self)
+                case (.vertical, _):
+                    frame.origin.y = (leadingEdgePosition - insets.top).roundedToPixel(in: self)
+                @unknown default:
+                    fatalError("Unknown user interface layout direction")
                 }
 
                 applyOrthogonalAlignment(&frame, layoutBounds)
@@ -287,9 +291,9 @@ extension UIView {
 
             switch (axis, receiverLayoutDirection) {
             case (.horizontal, .leftToRight), (.vertical, _):
-                viewOrigin += distanceToMoveOrigin
+                leadingEdgePosition += distanceToMoveOrigin
             case (.horizontal, .rightToLeft):
-                viewOrigin -= distanceToMoveOrigin
+                leadingEdgePosition -= distanceToMoveOrigin
             @unknown default:
                 fatalError("Unknown user interface layout direction")
             }