NSLayoutManager

NSLayoutManager is a class in Apple's Text Kit framework that coordinates the layout and rendering of text. It sits between NSTextStorage, which holds the underlying characters and attributes, and NSTextContainer, which defines the region where text is laid out. An NSLayoutManager can manage multiple NSTextContainers, allowing text to be laid out across several regions or views.

Its responsibilities include creating and mapping glyphs from characters, laying out lines, handling hyphenation and justification, wrapping and truncation, and drawing the laid-out glyphs within the containers’ coordinate system. It provides conversions between character ranges and glyph ranges and a drawing API to render glyphs at a specified point.

Interaction with the system is provided through the NSLayoutManagerDelegate protocol, which enables customization of layout behavior such as line fragment rectangles, glyph generation, and invalidation. When the NSTextStorage changes, the layout manager recalculates the layout and informs its text containers to redraw.

Typical usage: a single layout manager can back a NSTextView or other views; multiple text containers can share the same layout manager, enabling non-uniform layouts. The component is central to rich text editing and complex typography beyond simple labels.

History: NSLayoutManager was introduced with Text Kit in OS X 10.8 and iOS 7 and remains a core element of advanced text rendering in Apple platforms.