didModifyRange

DidModifyRange is a method associated with the text system used by Cocoa and Cocoa Touch, primarily within the NSTextStorage class of the Text Kit architecture. It serves as a hook for notifying that a specific portion of the text storage has been changed.

In the text system, edits to a text storage can affect its layout and rendering. didModifyRange provides a targeted signal indicating that the characters within a given range were modified, allowing dependent components such as layout managers to focus work only on the affected portion rather than performing a full refresh. The exact behavior is typically implemented by subclasses of NSTextStorage or by components that manage or observe text storage.

The method is generally considered a lower-level notification. It is often used in conjunction with other editing APIs, such as the standard edited:range:changeInLength: notifications, to coordinate incremental updates across the text system. The default implementation of didModifyRange does not impose any specific action, so implementations that need to react to range-specific changes must override it.

Practical implications include more efficient rendering and layout updates when only a subset of text changes, avoiding unnecessary work on unchanged regions. Because didModifyRange is tied to the internal text system, it is primarily relevant to developers implementing custom text storage subclasses or extending text-handling behavior rather than to typical app-level text manipulation.

See also: NSTextStorage, NSLayoutManager, NSAttributedString, edited:range:changeInLength:.