Merge commit '7621e2f8dec938cf48181c8b10afc9b01f444e68' into beta

submodules/Components/HierarchyTrackingLayer/Sources/HierarchyTrackingLayer.swift

@@ -0,0 +1,33 @@
+import UIKit
+
+private final class NullActionClass: NSObject, CAAction {
+    @objc public func run(forKey event: String, object anObject: Any, arguments dict: [AnyHashable : Any]?) {
+    }
+}
+
+private let nullAction = NullActionClass()
+
+open class HierarchyTrackingLayer: CALayer {
+    public var didEnterHierarchy: (() -> Void)?
+    public var didExitHierarchy: (() -> Void)?
+    public var isInHierarchyUpdated: ((Bool) -> Void)?
+    
+    public private(set) var isInHierarchy: Bool = false {
+        didSet {
+            if self.isInHierarchy != oldValue {
+                self.isInHierarchyUpdated?(self.isInHierarchy)
+            }
+        }
+    }
+    
+    override open func action(forKey event: String) -> CAAction? {
+        if event == kCAOnOrderIn {
+            self.isInHierarchy = true
+            self.didEnterHierarchy?()
+        } else if event == kCAOnOrderOut {
+            self.isInHierarchy = false
+            self.didExitHierarchy?()
+        }
+        return nullAction
+    }
+}