sitapix/txt-snippets

Text Recipes

Authored against iOS 26.x / Swift 6.x / Xcode 26.x.

This skill is a catalog of working snippets for the small, recurring "how do I add X to a text view" tasks. Each recipe is intended to drop into a project with minimal adjustment. The patterns here are starting points, not final code — verify the integration in the actual project before claiming the recipe matches what's needed, and confirm any API used here against current Apple docs via Sosumi if the snippet is a few releases old.

The five most-asked recipes are inlined below. The full catalog of twenty recipes lives in references/recipes.md, grouped by topic.

Contents

• Placeholder text in UITextView
• Character or word limit
• Auto-growing text view
• Highlight search results
• Auto-detect links and data
• Full recipe index
• Common Mistakes
• References

Placeholder text in UITextView

UITextView has no built-in placeholder. Subclass and draw the placeholder when the text is empty, then invalidate display whenever text or placeholder changes.

class PlaceholderTextView: UITextView {
    var placeholder: String = "" { didSet { setNeedsDisplay() } }
    override var text: String! { didSet { setNeedsDisplay() } }

    override func draw(_ rect: CGRect) {
        super.draw(rect)
        guard text.isEmpty else { return }
        let inset = textContainerInset
        let pad = textContainer.lineFragmentPadding
        let drawRect = CGRect(
            x: inset.left + pad,
            y: inset.top,
            width: bounds.width - inset.left - inset.right - 2 * pad,
            height: bounds.height - inset.top - inset.bottom
        )
        placeholder.draw(in: drawRect, withAttributes: [
            .font: font ?? .systemFont(ofSize: 17),
            .foregroundColor: UIColor.placeholderText
        ])
    }
}

Hook the host's textViewDidChange(_:) (or NSText.didChangeNotification) to call setNeedsDisplay() on every keystroke so the placeholder appears as soon as the text becomes empty again.

Character or word limit

Enforce a limit in shouldChangeTextIn:replacementText:. Compute the would-be length first; reject the edit if it exceeds the cap.

func textView(_ textView: UITextView,
              shouldChangeTextIn range: NSRange,
              replacementText text: String) -> Bool {
    let current = (textView.text as NSString).length
    let newLength = current - range.length + (text as NSString).length
    return newLength <= 280
}

Use NSString length for the math — Swift String.count returns grapheme clusters, which diverges from NSRange units on emoji and combining marks. For word limits, count text.split(separator: " ", omittingEmptySubsequences: true).count against the projected text after the edit.

Auto-growing text view

A UITextView reports a non-trivial intrinsicContentSize only when scrolling is disabled. Disable scrolling, let Auto Layout drive the height, and re-enable scrolling once a maximum height is reached.

textView.isScrollEnabled = false   // intrinsicContentSize now drives layout
textView.heightAnchor.constraint(lessThanOrEqualToConstant: 200).isActive = true

func textViewDidChange(_ textView: UITextView) {
    let fits = textView.sizeThatFits(
        CGSize(width: textView.bounds.width, height: .greatestFiniteMagnitude)
    )
    textView.isScrollEnabled = fits.height > 200
}

If the view is inside a stack or scroll view, ensure the parent honors the changed intrinsic size — a sibling with lowest content-hugging priority can absorb the growth instead of the editor.

Highlight search results

Mutating attributedText to highlight matches invalidates layout and disturbs typing attributes. Use the layout manager's temporary attributes on TextKit 1 — they live above the storage and don't enter the editing lifecycle.

func highlight(_ query: String, in textView: UITextView) {
    guard let lm = textView.layoutManager, let text = textView.text else { return }
    let full = NSRange(location: 0, length: (text as NSString).length)
    lm.removeTemporaryAttribute(.backgroundColor, forCharacterRange: full)

    var search = text.startIndex..<text.endIndex
    while let r = text.range(of: query, options: .caseInsensitive, range: search) {
        lm.addTemporaryAttribute(.backgroundColor,
                                 value: UIColor.systemYellow,
                                 forCharacterRange: NSRange(r, in: text))
        search = r.upperBound..<text.endIndex
    }
}

Note: accessing layoutManager flips a TextKit 2 UITextView to TextKit 1 permanently. On TextKit 2, use setRenderingAttributes(_:for:) on the layout manager instead — same effect, no fallback. See txt-fallback-triggers.

Auto-detect links and data

Built-in detection in UITextView requires a non-editable view. The data-detector property is silently ignored when editing is enabled.

textView.isEditable = false
textView.dataDetectorTypes = [.link, .phoneNumber, .address, .calendarEvent]

For editable text views, run NSDataDetector over the content and apply .link attributes to the matched ranges manually. See txt-detectors-tagger for the detector setup.

Full recipe index

The complete catalog lives in references/recipes.md:

| # | Recipe | |---|--------| | 1 | Background color behind a paragraph | | 2 | Line numbers in a text view | | 3 | Character or word limit on input | | 4 | Text wrapping around an image | | 5 | Clickable links (read-only) | | 6 | Clickable links (editable) | | 7 | Placeholder text in UITextView | | 8 | Auto-growing text view | | 9 | Highlight search results | | 10 | Strikethrough text | | 11 | Letter spacing (tracking and kern) | | 12 | Different line heights per paragraph | | 13 | First-line indent on paragraphs | | 14 | Bullet or numbered lists | | 15 | Read-only styled text | | 16 | Auto-detect data (phones, URLs, dates) | | 17 | Custom cursor color | | 18 | Disable text selection | | 19 | Programmatically scroll to range | | 20 | Get current line number | | 21 | Strip formatting on paste | | 22 | Convert AttributedString ↔ NSAttributedString | | 23 | Export NSAttributedString to RTF / HTML | | 24 | Suppress autocorrect / smart punctuation | | 25 | Auto-resizing UITextView in SwiftUI | | 26 | Smart pairs and auto-indent (cursor-stable) | | 27 | Tree-sitter concurrent reparse | | 28 | Modern keyboard avoidance with keyboardLayoutGuide |

Recipes show UIKit code by default. Recipes that touch only NSTextStorage, NSAttributedString, or NSParagraphStyle work on AppKit unchanged. UIKit-specific surfaces (UITextView, content-size category, dataDetectorTypes) need the AppKit equivalent — see the platform-translation table at the top of references/recipes.md.

Common Mistakes

1. dataDetectorTypes on an editable text view. Silently ignored. Detection only runs on isEditable = false views; for editable views, run NSDataDetector and apply attributes yourself.

2. String.count for NSRange math. Counts graphemes, not UTF-16 code units. Wrong on emoji and combining marks. Use (text as NSString).length or NSRange(swiftRange, in: text).

3. Mutating attributedText to highlight matches. Invalidates layout, disturbs typing attributes, and on TextKit 2 forces a full re-render. Use temporary attributes (TK1) or rendering attributes (TK2) instead.

4. Auto-grow with isScrollEnabled = true. UIKit reports UIView.noIntrinsicMetric for the height while scrolling is enabled. Disable scrolling first, then conditionally re-enable past a maximum height.

5. Forgetting to invalidate display on placeholder change. The placeholder is drawn in draw(_:). Without setNeedsDisplay(), the previous placeholder lingers until the next layout pass.

References

• references/recipes.md — full catalog of 20 recipes with code
• /skill txt-view-picker — picking a text view in the first place
• /skill txt-line-breaking — paragraph style internals (line height, spacing, tab stops)
• /skill txt-attribute-keys — formatting attribute catalog
• /skill txt-measurement — sizing text and views to fit content
• /skill txt-detectors-tagger — NSDataDetector for editable views
• /skill txt-fallback-triggers — TextKit 2 → 1 fallback when accessing layoutManager