Fix split views on Catalyst

Prevent resizeHandler() from being called twice in one pass

Author: bbrk24

.github/workflows/build-test-and-docs.yml

@@ -173,8 +173,7 @@ jobs:
         buildtarget RandomNumberGeneratorExample
         buildtarget WebViewExample
         buildtarget AdvancedCustomizationExample
-        # TODO test whether this works on Catalyst
-        # buildtarget SplitExample
+        buildtarget SplitExample
 
   windows:
     runs-on: windows-latest

Examples/Bundler.toml

@@ -35,6 +35,10 @@ identifier = 'dev.swiftcrossui.SplitExample'
 product = 'SplitExample'
 version = '0.1.0'
 
+[[apps.SplitExample.overlays]]
+condition = "platform(macCatalyst)"
+interface_idiom = "mac"
+
 [apps.SpreadsheetExample]
 identifier = 'dev.swiftcrossui.SpreadsheetExample'
 product = 'SpreadsheetExample'

Sources/UIKitBackend/UIKitBackend+SplitView.swift

@@ -1,20 +1,71 @@
 import UIKit
 
-#if os(iOS)
+#if os(iOS) || targetEnvironment(macCatalyst)
     final class SplitWidget: WrapperControllerWidget<UISplitViewController>,
         UISplitViewControllerDelegate
     {
-        var resizeHandler: (() -> Void)?
-        private let sidebarContainer: ContainerWidget
-        private let mainContainer: ContainerWidget
+        private final class ColumnView: UIView {
+            unowned var splitWidget: SplitWidget!
+
+            @available(*, unavailable)
+            required init?(coder: NSCoder) {
+                fatalError("init(coder:) is not used for this view")
+            }
+
+            init() {
+                super.init(frame: .zero)
+            }
+
+            override func layoutSubviews() {
+                super.layoutSubviews()
+                if !splitWidget.hasCalledResizeHandler {
+                    splitWidget.resizeHandler?()
+                    splitWidget.hasCalledResizeHandler = true
+                }
+            }
+        }
+
+        private final class ColumnWidget: ContainerWidget {
+            let columnView = ColumnView()
+
+            override func loadView() {
+                view = columnView
+            }
+        }
+
+        var resizeHandler: (() -> Void)? {
+            didSet {
+                hasCalledResizeHandler = false
+            }
+        }
+
+        // This is just a flag so that we don't call resizeHandler twice in one pass through the run loop.
+        var hasCalledResizeHandler = false {
+            willSet {
+                if newValue {
+                    DispatchQueue.main.async { [weak self] in
+                        self?.hasCalledResizeHandler = false
+                    }
+                }
+            }
+        }
+
+        private let sidebarContainer: ColumnWidget
+        private let mainContainer: ColumnWidget
 
         init(sidebarWidget: some WidgetProtocol, mainWidget: some WidgetProtocol) {
             // UISplitViewController requires its children to be controllers, not views
-            sidebarContainer = ContainerWidget(child: sidebarWidget)
-            mainContainer = ContainerWidget(child: mainWidget)
+            sidebarContainer = ColumnWidget(child: sidebarWidget)
+            mainContainer = ColumnWidget(child: mainWidget)
 
             super.init(child: UISplitViewController())
 
+            sidebarContainer.parentWidget = self
+            mainContainer.parentWidget = self
+            childWidgets = [sidebarContainer, mainContainer]
+            sidebarContainer.columnView.splitWidget = self
+            mainContainer.columnView.splitWidget = self
+
             child.delegate = self
 
             child.preferredDisplayMode = .oneBesideSecondary
@@ -45,11 +96,6 @@ import UIKit
 
             super.viewDidLoad()
         }
-
-        override func viewDidLayoutSubviews() {
-            super.viewDidLayoutSubviews()
-            resizeHandler?()
-        }
     }
 
     extension UIKitBackend {