Extension on UITextView that allows for the detection of truncation.

UITextView+Truncated.swift

extension UITextView {
  // Massive credit to Dave Delong for his extensive help with this solution.
  /// Returns whether or not the `UITextView` is displaying truncated text. This includes text
  /// that is visually truncated with an ellipsis (...), and text that is simply cut off through
  /// word wrapping.
  ///
  /// - Important:
  /// This only works properly when the `NSLineBreakMode` is set to `.byTruncatingTail` or `.byWordWrapping`.
  ///
  /// - Remark:
  /// Calculation enumerates over all line fragments that the textview's LayoutManger generates
  /// and checks for the presence of the truncation glyph. If the textview's `NSLineBreakMode` is
  /// not set to `.byTruncatingTail` this calculation will be based on whether the textview's
  /// character content extends beyond its view frame.
  var isTextTruncated: Bool {
    var isTruncating = false

    // The `truncatedGlyphRange(...) method will tell us if text has been truncated
    // based on the line break mode of the text container
    layoutManager.enumerateLineFragments(forGlyphRange: NSRange(location: 0, length: Int.max)) { _, _, _, glyphRange, stop in
      let truncatedRange = self.layoutManager.truncatedGlyphRange(inLineFragmentForGlyphAt: glyphRange.lowerBound)
      if truncatedRange.location != NSNotFound {
        isTruncating = true
        stop.pointee = true
      }
    }

    // It's possible that the text is truncated not because of the line break mode,
    // but because the text is outside the drawable bounds
    if isTruncating == false {
      let glyphRange = layoutManager.glyphRange(for: textContainer)
      let characterRange = layoutManager.characterRange(forGlyphRange: glyphRange, actualGlyphRange: nil)

      isTruncating = characterRange.upperBound < text.utf16.count
    }

    return isTruncating
  }
}

Hi.

First. Thanks for your hard work.

It helped me a lot but for me and my coder under iOS 15.2 the truncatedGlyphRange method doesn't return the range of the truncated glyph. E.g. when I use a word like "Mmmmmm...(m repeating)".

So my UITextView doesn't show the last m but the function doesn't tell me that the text is truncated.
lineBreakMode is .byWordWrapping and scrolling disabled maximumNumberOfLines = 0

Maybe some weird behavior in my code ?

Works perfectly, thank you sincerely.