TextKit 2 Reference

Complete reference for TextKit 2 covering architecture, migration from TextKit 1, Writing Tools integration, and SwiftUI TextEditor with AttributedString through iOS 26.

Architecture

TextKit 2 uses MVC pattern with new classes optimized for correctness, safety, and performance.

Model Layer

NSTextContentManager (abstract)

• Generates NSTextElement objects from backing store

• Tracks element ranges within document

• Default implementation: NSTextContentStorage

NSTextContentStorage

• Uses NSTextStorage as backing store

• Automatically divides content into NSTextParagraph elements

• Generates updated elements when text changes

NSTextElement (abstract)

• Represents portion of content (paragraph, attachment, custom type)

• Immutable value semantics

• Properties cannot change after creation

• Default implementation: NSTextParagraph

NSTextParagraph

• Represents single paragraph

• Contains range within document

Controller Layer

NSTextLayoutManager

• Replaces TextKit 1's NSLayoutManager

• NO glyph APIs (abstracts away glyphs entirely)

• Takes elements, lays out into container, generates layout fragments

• Always uses noncontiguous layout

NSTextLayoutFragment

• Immutable layout information for one or more elements

• Key properties:

• textLineFragments — array of NSTextLineFragment

• layoutFragmentFrame — layout bounds within container

• renderingSurfaceBounds — actual drawing bounds (can exceed frame)

NSTextLineFragment

• Measurement info for single line of text

• Used for line counting and geometric queries

View Layer

NSTextViewportLayoutController

• Source of truth for viewport layout

• Coordinates visible-only layout

• Calls delegate methods: willLayout , configureRenderingSurface , didLayout

NSTextContainer

• Provides geometric information for layout destination

• Can define exclusion paths (non-rectangular layout)

Object-Based Ranges

NSTextLocation (protocol)

• Represents single location in text

• Replaces integer indices

• Supports structured documents (e.g., DOM with nested elements)

NSTextRange

• Start and end locations (end is excluded)

• Can represent nested structure

• Incompatible with NSRange for non-linear documents

NSTextSelection

• Contains: granularity, affinity, possibly disjoint ranges

• Read-only properties

• Immutable value semantics

NSTextSelectionNavigation

• Performs actions on selections

• Returns new NSTextSelection instances

• Handles bidirectional text correctly

Core Design Principles

1. Correctness — No Glyph APIs

From WWDC 2021:

"TextKit 2 abstracts away glyph handling to provide a consistent experience for international text."

Why no glyphs?

Problem: In scripts like Kannada and Arabic:

• One glyph can represent multiple characters (ligatures)

• One character can split into multiple glyphs

• Glyphs reorder during shaping

• No correct character→glyph mapping

Example (Kannada word "October"):

• Character 4 splits into 2 glyphs

• Glyphs reorder before ligature application

• Glyph 3 becomes conjoining form and moves below another glyph

Solution: Use NSTextLocation, NSTextRange, NSTextSelection instead of glyph indices.

2. Safety — Value Semantics

Immutable objects:

• NSTextElement

• NSTextLayoutFragment

• NSTextLineFragment

• NSTextSelection

Benefits:

• No unintended sharing

• No side effects from mutations

• Easier to reason about state

Pattern: To change layout/selection, create new instances with desired changes.

3. Performance — Viewport Layout

Always Noncontiguous: TextKit 2 performs layout only for visible content + overscroll region.

TextKit 1:

• Optional noncontiguous layout (boolean property)

• No visibility into layout state

• Can't control which parts get laid out

TextKit 2:

• Always noncontiguous

• Viewport defines visible area

• Consistent layout info for viewport

• Notifications for viewport layout updates

Viewport Delegate Methods:

• textViewportLayoutControllerWillLayout(_:) — setup before layout

• textViewportLayoutController(_:configureRenderingSurfaceFor:) — per fragment

• textViewportLayoutControllerDidLayout(_:) — cleanup after layout

Migration from TextKit 1

Key Paradigm Shift

TextKit 1 TextKit 2

Glyphs Elements

NSRange NSTextLocation/NSTextRange

NSLayoutManager NSTextLayoutManager

Glyph APIs NO glyph APIs

Optional noncontiguous Always noncontiguous

NSTextStorage directly Via NSTextContentManager

API Naming Heuristics

From WWDC 2022:

• .offset in name → TextKit 1

• .location in name → TextKit 2

NSRange ↔ NSTextRange Conversion

NSRange → NSTextRange:

// UITextView/NSTextView let nsRange = NSRange(location: 0, length: 10)

// Via content manager let startLocation = textContentManager.location( textContentManager.documentRange.location, offsetBy: nsRange.location )! let endLocation = textContentManager.location( startLocation, offsetBy: nsRange.length )! let textRange = NSTextRange(location: startLocation, end: endLocation)

NSTextRange → NSRange:

let startOffset = textContentManager.offset( from: textContentManager.documentRange.location, to: textRange.location ) let length = textContentManager.offset( from: textRange.location, to: textRange.endLocation ) let nsRange = NSRange(location: startOffset, length: length)

Glyph API Replacements

NO direct glyph API equivalents. Must use higher-level structures.

Example (TextKit 1 - counting lines):

// TextKit 1 - iterate glyphs var lineCount = 0 let glyphRange = layoutManager.glyphRange(for: textContainer) for glyphIndex in glyphRange.location..<NSMaxRange(glyphRange) { let lineRect = layoutManager.lineFragmentRect( forGlyphAt: glyphIndex, effectiveRange: nil ) // Count unique rects... }

Replacement (TextKit 2 - enumerate fragments):

// TextKit 2 - enumerate layout fragments var lineCount = 0 textLayoutManager.enumerateTextLayoutFragments( from: textLayoutManager.documentRange.location, options: [.ensuresLayout] ) { fragment in lineCount += fragment.textLineFragments.count return true }

Compatibility Mode (UITextView/NSTextView)

Automatic Fallback to TextKit 1: Happens when you access .layoutManager property.

Warning (WWDC 2022):

"Accessing textView.layoutManager triggers TK1 fallback"

Once fallback occurs:

• No automatic way back to TextKit 2

• Expensive to switch

• Lose UI state (selection, scroll position)

• One-way operation

Prevent Fallback:

• Check .textLayoutManager first (TextKit 2)

• Only access .layoutManager in else clause

• Opt out at initialization if TK1 required

// Check TextKit 2 first if let textLayoutManager = textView.textLayoutManager { // TextKit 2 code } else if let layoutManager = textView.layoutManager { // TextKit 1 fallback (old OS versions) }

Debug Fallback:

• UIKit: Breakpoint on _UITextViewEnablingCompatibilityMode

• AppKit: Subscribe to willSwitchToNSLayoutManagerNotification

NSTextView Opt-In (macOS)

Create TextKit 2 NSTextView:

let textLayoutManager = NSTextLayoutManager() let textContainer = NSTextContainer() textLayoutManager.textContainer = textContainer

let textView = NSTextView(frame: .zero, textContainer: textContainer) // textView.textLayoutManager now available

New Convenience Constructor:

// iOS 16+ / macOS 13+ let textView = UITextView(usingTextLayoutManager: true) let nsTextView = NSTextView(usingTextLayoutManager: true)

Delegate Hooks

NSTextContentStorageDelegate

Customize attributes without modifying storage:

func textContentStorage( _ textContentStorage: NSTextContentStorage, textParagraphWith range: NSRange ) -> NSTextParagraph? { // Modify attributes for display var attributedString = textContentStorage.attributedString! .attributedSubstring(from: range)

// Add custom attributes
if isComment(range) {
    attributedString.addAttribute(
        .foregroundColor,
        value: UIColor.systemIndigo,
        range: NSRange(location: 0, length: attributedString.length)
    )
}

return NSTextParagraph(attributedString: attributedString)

}

Filter elements (hide/show content):

func textContentManager( _ textContentManager: NSTextContentManager, shouldEnumerate textElement: NSTextElement, options: NSTextContentManager.EnumerationOptions ) -> Bool { // Return false to hide element if hideComments && isComment(textElement) { return false } return true }

NSTextLayoutManagerDelegate

Provide custom layout fragments:

func textLayoutManager( _ textLayoutManager: NSTextLayoutManager, textLayoutFragmentFor location: NSTextLocation, in textElement: NSTextElement ) -> NSTextLayoutFragment { // Return custom fragment for special styling if isComment(textElement) { return BubbleLayoutFragment( textElement: textElement, range: textElement.elementRange ) } return NSTextLayoutFragment( textElement: textElement, range: textElement.elementRange ) }

NSTextViewportLayoutController.Delegate

Viewport layout lifecycle:

func textViewportLayoutControllerWillLayout(_ controller: NSTextViewportLayoutController) { // Prepare for layout: clear sublayers, begin animation }

func textViewportLayoutController( _ controller: NSTextViewportLayoutController, configureRenderingSurfaceFor textLayoutFragment: NSTextLayoutFragment ) { // Update geometry for each visible fragment let layer = getOrCreateLayer(for: textLayoutFragment) layer.frame = textLayoutFragment.layoutFragmentFrame // Animate to new position if needed }

func textViewportLayoutControllerDidLayout(_ controller: NSTextViewportLayoutController) { // Finish: commit animations, update scroll indicators }

Practical Patterns

Custom Layout Fragment (Bubble Backgrounds)

class BubbleLayoutFragment: NSTextLayoutFragment { override func draw(at point: CGPoint, in context: CGContext) { // Draw custom background context.setFillColor(UIColor.systemIndigo.cgColor) let bubblePath = UIBezierPath( roundedRect: layoutFragmentFrame, cornerRadius: 8 ) context.addPath(bubblePath.cgPath) context.fillPath()

    // Draw text on top
    super.draw(at: point, in: context)
}

}

Rendering Attributes (Temporary Styling)

Add attributes that don't modify text storage:

textLayoutManager.addRenderingAttribute( .foregroundColor, value: UIColor.green, for: ingredientRange )

// Remove when no longer needed textLayoutManager.removeRenderingAttribute( .foregroundColor, for: ingredientRange )

Text Attachment with UIView

// iOS 15+ let attachment = NSTextAttachment() attachment.image = UIImage(systemName: "star.fill")

// Provide view for interaction class AttachmentViewProvider: NSTextAttachmentViewProvider { override func loadView() { super.loadView() let button = UIButton(type: .system) button.setTitle("Tap me", for: .normal) button.addTarget(self, action: #selector(didTap), for: .touchUpInside) view = button }

@objc func didTap() {
    // Handle tap
}

}

Lists and Tables

// Create list let listItem = NSTextList(markerFormat: .disc, options: 0) let paragraphStyle = NSMutableParagraphStyle() paragraphStyle.textLists = [listItem]

attributedString.addAttribute( .paragraphStyle, value: paragraphStyle, range: range )

NSTextList available in UIKit (iOS 16+), previously AppKit-only.

Hit Testing & Selection Geometry

// Get text range at point let location = textLayoutManager.location( interactingAt: point, inContainerAt: textContainer.location )

// Get bounding rect for range var boundingRect = CGRect.zero textLayoutManager.enumerateTextSegments( in: textRange, type: .standard, options: [] ) { segmentRange, segmentRect, baselinePosition, textContainer in boundingRect = boundingRect.union(segmentRect) return true }

Writing Tools (iOS 18+)

Basic Integration (TextKit 2 Required)

From WWDC 2024:

"UITextView or NSTextView has to use TextKit 2 to support the full Writing Tools experience. If using TextKit 1, you will get a limited experience that just shows rewritten results in a panel."

Free for native text views:

// UITextView, NSTextView, WKWebView // Writing Tools appears automatically

Lifecycle Delegate Methods

func textViewWritingToolsWillBegin(_ textView: UITextView) { // Pause syncing, prevent edits isSyncing = false }

func textViewWritingToolsDidEnd(_ textView: UITextView) { // Resume syncing isSyncing = true }

// Check if active if textView.isWritingToolsActive { // Don't persist text storage }

Controlling Behavior

// Opt out completely textView.writingToolsBehavior = .none

// Panel-only experience (no in-line edits) textView.writingToolsBehavior = .limited

// Full experience (default) textView.writingToolsBehavior = .default

Result Options

// Plain text only textView.writingToolsResultOptions = [.plainText]

// Rich text textView.writingToolsResultOptions = [.richText]

// Rich text + tables textView.writingToolsResultOptions = [.richText, .table]

// Rich text + lists textView.writingToolsResultOptions = [.richText, .list]

Protected Ranges

// UITextViewDelegate / NSTextViewDelegate func textView( _ textView: UITextView, writingToolsIgnoredRangesIn enclosingRange: NSRange ) -> [NSRange] { // Return ranges that Writing Tools should not modify return codeBlockRanges + quoteRanges }

WKWebView: <blockquote> and <pre> tags automatically ignored.

Writing Tools Coordinator (iOS 26+)

Advanced integration for custom text engines.

Setup

// UIKit let coordinator = UIWritingToolsCoordinator() coordinator.delegate = self textView.addInteraction(coordinator) coordinator.writingToolsBehavior = .default coordinator.writingToolsResultOptions = [.richText]

// AppKit let coordinator = NSWritingToolsCoordinator() coordinator.delegate = self customView.writingToolsCoordinator = coordinator

Coordinator Delegate

Provide context:

func writingToolsCoordinator( _ coordinator: NSWritingToolsCoordinator, requestContexts scope: NSWritingToolsCoordinator.ContextScope ) async -> [NSWritingToolsCoordinator.Context] { // Return attributed string + selection range let context = NSWritingToolsCoordinator.Context( attributedString: currentText, range: currentSelection ) return [context] }

Apply changes:

func writingToolsCoordinator( _ coordinator: NSWritingToolsCoordinator, replace context: NSWritingToolsCoordinator.Context, range: NSRange, with attributedString: NSAttributedString ) async { // Update text storage textStorage.replaceCharacters(in: range, with: attributedString) }

Update selection:

func writingToolsCoordinator( _ coordinator: NSWritingToolsCoordinator, updateSelectedRange selectedRange: NSRange, in context: NSWritingToolsCoordinator.Context ) async { // Update selection self.selectedRange = selectedRange }

Provide previews for animation:

// macOS func writingToolsCoordinator( _ coordinator: NSWritingToolsCoordinator, previewsFor context: NSWritingToolsCoordinator.Context, range: NSRange ) async -> [NSTextPreview] { // Return one preview per line for smooth animation return textLines.map { line in NSTextPreview( image: renderImage(for: line), frame: line.frame ) } }

// iOS func writingToolsCoordinator( _ coordinator: UIWritingToolsCoordinator, previewFor context: UIWritingToolsCoordinator.Context, range: NSRange ) async -> UITargetedPreview { // Return single preview return UITargetedPreview( view: previewView, parameters: parameters ) }

Proofreading marks:

func writingToolsCoordinator( _ coordinator: NSWritingToolsCoordinator, underlinesFor context: NSWritingToolsCoordinator.Context, range: NSRange ) async -> [NSValue] { // Return bezier paths for underlines return ranges.map { range in let path = bezierPath(for: range) return NSValue(bytes: &path, objCType: "CGPath") } }

PresentationIntent (iOS 26+)

Semantic rich text result option:

coordinator.writingToolsResultOptions = [.richText, .presentationIntent]

Difference from display attributes:

Display attributes (bold, italic):

• Concrete font info (point sizes, font names)

• No semantic meaning

PresentationIntent (header, code block, emphasis):

• Semantic style info

• App converts to internal styles

• Lists, tables, code blocks use presentation intent

• Underline, subscript, superscript still use display attributes

Example:

// Check for presentation intent if attributedString.runs[.presentationIntent].contains(where: { $0?.components.contains(.header(level: 1)) == true }) { // This is a heading }

SwiftUI TextEditor + AttributedString (iOS 26+)

Basic Usage

struct RecipeEditor: View { @State private var text: AttributedString = "Recipe text"

var body: some View {
    TextEditor(text: $text)
}

}

Supported attributes:

• Bold, italic, underline, strikethrough

• Custom fonts, point size

• Foreground and background colors

• Kerning, tracking, baseline offset

• Genmoji

• Line height, text alignment, base writing direction

TextAlignment and WritingDirection

// Text alignment (AttributedString.TextAlignment) var text = AttributedString("Centered paragraph") text.alignment = .center // .left, .right, .center

// Writing direction for bidirectional text var bidiText = AttributedString("Hello عربي") bidiText.writingDirection = .rightToLeft // .leftToRight, .rightToLeft

LineHeight Control

var multiline = AttributedString("Paragraph\nwith multiple\nlines.") multiline.lineHeight = .exact(points: 32) // Fixed height multiline.lineHeight = .multiple(factor: 2.5) // Multiplier multiline.lineHeight = .loose // System loose spacing

Selection Binding

@State private var selection: AttributedTextSelection?

TextEditor(text: $text, selection: $selection)

AttributedTextSelection:

enum AttributedTextSelection { case none case single(NSRange) case multiple(Set<NSRange>) // For bidirectional text }

Get selected text:

if let selection { let selectedText: AttributedSubstring switch selection.indices { case .none: selectedText = text[...] case .single(let range): selectedText = text[range] case .multiple(let ranges): // Discontiguous substring from RangeSet selectedText = text[selection] } }

Programmatic Selection Replacement

var text = AttributedString("Here is my dog") var selection = AttributedTextSelection(range: text.range(of: "dog")!)

// Replace with plain text text.replaceSelection(&selection, withCharacters: "cat")

// Replace with attributed content let replacement = AttributedString("horse") text.replaceSelection(&selection, with: replacement)

DiscontiguousAttributedSubstring

Work with non-contiguous selections using RangeSet :

let text = AttributedString("Select multiple parts of this text") let range1 = text.range(of: "Select")! let range2 = text.range(of: "text")! let rangeSet = RangeSet([range1, range2]) var substring = text[rangeSet] // DiscontiguousAttributedSubstring substring.backgroundColor = .yellow

// Convert back to AttributedString let combined = AttributedString(substring)

Text Selection Affinity

Control selection affinity for the view hierarchy:

TextEditor(text: $text, selection: $selection) .textSelectionAffinity(.upstream) // .upstream or .downstream

Use .upstream when selection should resolve toward the beginning of text at line boundaries.

Custom Formatting Definition

Constrain which attributes are editable:

struct RecipeFormattingDefinition: AttributedTextFormattingDefinition { typealias FormatScope = RecipeAttributeScope

static let constraints: [any AttributedTextValueConstraint<RecipeFormattingDefinition>] = [
    IngredientsAreGreen()
]

}

struct RecipeAttributeScope: AttributedScope { var ingredient: IngredientAttribute var foregroundColor: ForegroundColorAttribute var genmoji: GenmojiAttribute }

Apply to TextEditor:

TextEditor(text: $text) .attributedTextFormattingDefinition(RecipeFormattingDefinition.self)

Value Constraints

Control attribute values based on custom logic:

struct IngredientsAreGreen: AttributedTextValueConstraint { typealias Definition = RecipeFormattingDefinition typealias AttributeKey = ForegroundColorAttribute

func constrain(
    _ value: inout Color?,
    in scope: RecipeFormattingDefinition.FormatScope
) {
    if scope.ingredient != nil {
        value = .green // Ingredients are always green
    } else {
        value = nil // Others use default
    }
}

}

System behavior:

• TextEditor probes constraints to determine if changes are valid

• If constraint would revert change, control is disabled

• Constraints applied to pasted content

Custom Attributes

Define attribute:

struct IngredientAttribute: CodableAttributedStringKey { typealias Value = UUID // Ingredient ID

static let name = "ingredient"

}

extension AttributeScopes.RecipeAttributeScope { var ingredient: IngredientAttribute.Type { IngredientAttribute.self } }

Attribute behavior:

extension IngredientAttribute { // Don't expand when typing after ingredient static let inheritedByAddedText = false

// Remove if text in run changes
static let invalidationConditions: [AttributedString.InvalidationCondition] = [
    .textChanged
]

// Optional: constrain to paragraph boundaries
static let runBoundaries: AttributedString.RunBoundaries = .paragraph

}

AttributedString Mutations

Safe index updates:

// Transform updates indices/selection during mutation text.transform(updating: &selection) { mutableText in // Find ranges let ranges = mutableText.characters.ranges(of: "butter")

// Set attribute for all ranges at once
for range in ranges {
    mutableText[range].ingredient = ingredientID
}

}

// selection is now updated to match transformed text

Don't use old indices:

// BAD - indices invalidated by mutation let range = text.characters.range(of: "butter")! text[range].foregroundColor = .green text.append(" (unsalted)") // range is now invalid!

AttributedString Views

Multiple views into same content:

• characters — grapheme clusters

• unicodeScalars — Unicode scalars

• utf8 — UTF-8 code units

• utf16 — UTF-16 code units

All views share same indices.

Known Limitations & Gotchas

Viewport Scroll Issues

From expert articles:

• Viewport can cause scroll position instability

• usageBoundsForTextContainer changes during scroll

• Apple's TextEdit exhibits same issues

• Trade-off for performance benefits

TextKit 1 Compatibility

• Accessing .layoutManager triggers fallback

• One-way operation (no automatic return)

• Loses UI state during switch

• Expensive to switch layout systems

AttributedString Index Invalidation

• Any mutation invalidates all indices

• Must use .transform(updating:) to keep indices valid

• Indices only work with originating AttributedString

Limited TextKit 1 Support

Unsupported in TextKit 2:

• NSTextTable (use NSTextList or custom layouts)

• Some legacy text attachments

• Direct glyph manipulation

Resources

WWDC: 2021-10061, 2022-10090, 2023-10058, 2024-10168, 2025-265, 2025-280

Docs: /uikit/nstextlayoutmanager, /appkit/textkit/using_textkit_2_to_interact_with_text, /uikit/display-text-with-a-custom-layout, /swiftui/building-rich-swiftui-text-experiences, /foundation/attributedstring, /foundation/attributedstring/textalignment, /foundation/attributedstring/lineheight, /foundation/discontiguousattributedsubstring, /uikit/writing-tools, /appkit/enhancing-your-custom-text-engine-with-writing-tools