View .onHover { Bool in } modifier

Examples/Bundler.toml

@@ -59,3 +59,8 @@ version = '0.1.0'
 identifier = 'dev.swiftcrossui.WebViewExample'
 product = 'WebViewExample'
 version = '0.1.0'
+
+[apps.HoverExample]
+identifier = 'dev.swiftcrossui.HoverExample'
+product = 'HoverExample'
+version = '0.1.0'

Examples/Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version: 5.9
+// swift-tools-version: 5.10
 
 import Foundation
 import PackageDescription
@@ -72,6 +72,10 @@ let package = Package(
         .executableTarget(
             name: "WebViewExample",
             dependencies: exampleDependencies
+        ),
+        .executableTarget(
+            name: "HoverExample",
+            dependencies: exampleDependencies
         )
     ]
 )

Examples/Sources/HoverExample/HoverApp.swift

@@ -0,0 +1,54 @@
+import DefaultBackend
+import Foundation
+import SwiftCrossUI
+
+#if canImport(SwiftBundlerRuntime)
+    import SwiftBundlerRuntime
+#endif
+
+@main
+struct HoverExample: App {
+    var body: some Scene {
+        WindowGroup("Hover Example") {
+            VStack(spacing: 0) {
+                ForEach([Bool](repeating: false, count: 18)) { _ in
+                    HStack(spacing: 0) {
+                        ForEach([Bool](repeating: false, count: 30)) { _ in
+                            CellView()
+                        }
+                    }
+                }
+            }
+            .background(Color.black)
+        }
+        .defaultSize(width: 900, height: 540)
+    }
+}
+
+struct CellView: View {
+    @State var timer: Timer?
+    @State var opacity: Float = 0.0
+
+    var body: some View {
+        Rectangle()
+            .foregroundColor(Color.blue.opacity(opacity))
+            .onHover { hovering in
+                if !hovering {
+                    timer = Timer.scheduledTimer(withTimeInterval: 0.05, repeats: true) { timer in
+                        DispatchQueue.main.async {
+                            if opacity >= 0.05 {
+                                opacity -= 0.05
+                            } else {
+                                opacity = 0.0
+                                timer.invalidate()
+                            }
+                        }
+                    }
+                } else {
+                    opacity = 1.0
+                    timer?.invalidate()
+                    timer = nil
+                }
+            }
+    }
+}

Sources/AppKitBackend/AppKitBackend.swift

@@ -1425,6 +1425,40 @@ public final class AppKitBackend: AppBackend {
         }
     }
 
+    public func createHoverTarget(wrapping child: Widget) -> Widget {
+        let container = NSView()
+
+        container.addSubview(child)
+        child.leadingAnchor.constraint(equalTo: container.leadingAnchor)
+            .isActive = true
+        child.topAnchor.constraint(equalTo: container.topAnchor)
+            .isActive = true
+        child.translatesAutoresizingMaskIntoConstraints = false
+
+        let hoverGestureTarget = NSCustomHoverTarget()
+        container.addSubview(hoverGestureTarget)
+        hoverGestureTarget.leadingAnchor.constraint(equalTo: container.leadingAnchor)
+            .isActive = true
+        hoverGestureTarget.topAnchor.constraint(equalTo: container.topAnchor)
+            .isActive = true
+        hoverGestureTarget.trailingAnchor.constraint(equalTo: container.trailingAnchor)
+            .isActive = true
+        hoverGestureTarget.bottomAnchor.constraint(equalTo: container.bottomAnchor)
+            .isActive = true
+        hoverGestureTarget.translatesAutoresizingMaskIntoConstraints = false
+
+        return container
+    }
+
+    public func updateHoverTarget(
+        _ container: Widget,
+        environment: EnvironmentValues,
+        action: @escaping (Bool) -> Void
+    ) {
+        let hoverGestureTarget = container.subviews[1] as! NSCustomHoverTarget
+        hoverGestureTarget.hoverChangesHandler = action
+    }
+
     final class NSBezierPathView: NSView {
         var path: NSBezierPath!
         var fillColor: NSColor = .clear
@@ -1663,7 +1697,7 @@ final class NSCustomTapGestureTarget: NSView {
                 leftClickRecognizer = gestureRecognizer
             } else if leftClickHandler == nil, let leftClickRecognizer {
                 removeGestureRecognizer(leftClickRecognizer)
-                self.leftClickHandler = nil
+                self.leftClickRecognizer = nil
             }
         }
     }
@@ -1678,7 +1712,7 @@ final class NSCustomTapGestureTarget: NSView {
                 rightClickRecognizer = gestureRecognizer
             } else if rightClickHandler == nil, let rightClickRecognizer {
                 removeGestureRecognizer(rightClickRecognizer)
-                self.rightClickHandler = nil
+                self.rightClickRecognizer = nil
             }
         }
     }
@@ -1724,6 +1758,60 @@ final class NSCustomTapGestureTarget: NSView {
     }
 }
 
+final class NSCustomHoverTarget: NSView {
+    var hoverChangesHandler: ((Bool) -> Void)? {
+        didSet {
+            if hoverChangesHandler != nil && trackingArea == nil {
+                let options: NSTrackingArea.Options = [
+                    .mouseEnteredAndExited,
+                    .activeInKeyWindow,
+                ]
+                let area = NSTrackingArea(
+                    rect: self.bounds,
+                    options: options,
+                    owner: self,
+                    userInfo: nil)
+                addTrackingArea(area)
+                trackingArea = area
+            } else if hoverChangesHandler == nil, let trackingArea {
+                // should be impossible at the moment of implementation
+                // keeping it to be save in case of later changes
+                removeTrackingArea(trackingArea)
+                self.trackingArea = nil
+            }
+        }
+    }
+
+    private var trackingArea: NSTrackingArea?
+
+    override func updateTrackingAreas() {
+        super.updateTrackingAreas()
+        if let trackingArea = trackingArea {
+            self.removeTrackingArea(trackingArea)
+        }
+        let options: NSTrackingArea.Options = [
+            .mouseEnteredAndExited,
+            .activeInKeyWindow,
+        ]
+
+        trackingArea = NSTrackingArea(
+            rect: self.bounds,
+            options: options,
+            owner: self,
+            userInfo: nil)
+        self.addTrackingArea(trackingArea!)
+    }
+
+    override func mouseEntered(with event: NSEvent) {
+        hoverChangesHandler?(true)
+    }
+
+    override func mouseExited(with event: NSEvent) {
+        // Mouse exited the view's bounds
+        hoverChangesHandler?(false)
+    }
+}
+
 final class NSCustomMenuItem: NSMenuItem {
     /// This property's only purpose is to keep a strong reference to the wrapped
     /// action so that it sticks around for long enough to be useful.