NSView

NSView is the foundational view class in macOS AppKit. It represents a rectangular region within a window, and it is responsible for drawing content, handling user input, and managing a hierarchy of subviews. NSView is a subclass of NSResponder, placing it in the macOS responder chain where it receives mouse, keyboard, and drag-and-drop events.

A view has a frame in its superview’s coordinate system and a bounds rectangle that describes its own coordinate space. Subviews are drawn in back-to-front order, and drawing is performed by overriding the drawRect: method or drawing with layer-backed content. A view can be marked for redisplay using setNeedsDisplay:, prompting the system to redraw during the next update cycle.

Coordinate systems in NSView are configurable. By default, the origin is at the bottom-left, but a view can override isFlipped to return true to adopt a top-left origin, which aligns with many modern UI layouts.

NSView supports layout and geometry management through the view hierarchy. It can have subviews and a superview, and provides methods to convert coordinates between views. It also participates in Auto Layout, with constraints used to define positions and sizes relative to other views.

Rendering performance can be enhanced by enabling layer-backed views via the wantsLayer property, which causes a CALayer to back the view. This enables hardware-accelerated compositing and animations, while preserving the view’s drawing and event-handling responsibilities.

Developers commonly subclass NSView to implement custom drawing, hit-testing, or interaction behavior. NSView remains a core building block for macOS interfaces, even as newer UI paradigms and SwiftUI evolve.