What is the difference between UIView and CALayer?

UIView is a high-level abstraction that provides interactivity (touch and gesture handling), a coordinate system for rendering content, and support for Auto Layout. It is a subclass of UIResponder.

CALayer is a low-level graphics primitive responsible for rendering visual content. CALayer is not a subclass of UIResponder and does not participate in the event chain. Each UIView has its own root CALayer (accessible via the layer property), which manages its visual presentation. CALayer is used for performing complex animations, transformations, and managing shadows, borders, and sublayer content.