Why is UIView needed if there is a layer (CALayer)?

UIView is the fundamental building block of the user interface in iOS. It is a subclass of NSResponder and handles touch events, manages subviews, and manages layout and rendering of content.

CALayer is a layer that provides the visual representation of a UIView's content. It does not participate in event handling or layout but manages properties such as position, size, transparency, borders, and shadows.

UIView exists to provide a high-level abstraction for user interaction and managing the visual presentation provided by CALayer. UIView delegates most of its drawing tasks to its associated CALayer but adds functionality for event handling, managing the view hierarchy, and supporting Auto Layout/Constraint-based Layout.

In short: CALayer is responsible for visual presentation, while UIView adds interactivity and hierarchy management.

// Example of creating a UIView and adding a subview
let parentView = UIView()
let childView = UIView()
parentView.addSubview(childView)
// childView also has an associated CALayer managed by UIView