Practical Dynamic Type, Part 3: Attributed Strings

dynamictype3-snippet5.swift

// MARK: Event Handlers

/// Update the sizes of all contained fonts whenever the Dynamic Type size changes.
@objc func uiContentSizeCategoryChanged() {

  /// Only continue if the `UILabel` has non-nil attributed text.
  guard let attributedString = display.attributedText else {
    return
  }

  /// Get the preexisting formatted string as a `NSMutableAttributedString` since we will
  /// modify the attributes directly in the `enumerateAttributes` loop.
  let mutableText = NSMutableAttributedString(attributedString: attributedString)

  /// Get the full range of the attributed text.
  let fullTextRange = NSRange(location: 0, length: mutableText.string.count)

  /// Enumerate over the full range of the formatted string and modify its attributes.
  mutableText.enumerateAttributes(in: fullTextRange, options: []) { attributes, range, stop in
    /// Get the `FontSetter` for this attributed substring
    guard let currentFontSetter = attributes[AttributedStringView.FontSetterAttributeKey]
      as? FontSetter else {
        fatalError("Could not read the FontSetter being enumerated over")
    }

    /// Execute the `FontSetter` block to regenerate the appropriate type size.
    let determinedFont = currentFontSetter()
                                                                   
    /// Check the new type size
    print("New font size (\(determinedFont.pointSize.description)) in range \(range)")

    /// Update the type size of the current substring with the new, appropriate type size.
    mutableText.addAttributes([.font : determinedFont], range: range)
  }

  /// Assign the new, updated formatted string to the `UILabel`.
  display.attributedText = mutableText
}