Why is UIView necessary if we already have CALayer?

UIView is a high-level abstraction that provides:

• Touch and gesture event handling.
• Management of the subview hierarchy.
• Support for Auto Layout and old Autoresizing Masks.
• Specialized behavior through subclasses (e.g., UIButton, UILabel, UIImageView).
• Integration with UIKit and the UIViewController lifecycle.
• A convenient invalidation and redraw mechanism (setNeedsDisplay()).

CALayer is a low-level Core Animation component responsible for visual representation:

• Contains a bitmap or graphic primitives for display.
• Handles positioning, transformations, shadows, borders, etc.
• Serves as the basis for animation.
• Does not directly handle touch events.

A UIView contains one or more CALayers to display its content and handle user interactions and other views in the hierarchy. CALayer, being more primitive, does not provide the same level of functionality for building user interfaces in UIKit.