UILabel extension with ReadMore/ ReadLess action

UILabel+Extensions.swift

import UIKit

enum TrailingContent {
    case readmore
    case readless

    var text: String {
        switch self {
        case .readmore: return "...Read More"
        case .readless: return " Read Less"
        }
    }
}

extension UILabel {

    private var minimumLines: Int { return 4 }
    private var highlightColor: UIColor { return .red }

    private var attributes: [NSAttributedString.Key: Any] {
        return [.font: self.font ?? .systemFont(ofSize: 18)]
    }
    
    public func requiredHeight(for text: String) -> CGFloat {
        let label = UILabel(frame: CGRect(x: 0, y: 0, width: frame.width, height: CGFloat.greatestFiniteMagnitude))
        label.numberOfLines = minimumLines
        label.lineBreakMode = NSLineBreakMode.byTruncatingTail
        label.font = font
        label.text = text
        label.sizeToFit()
        return label.frame.height
      }

    func highlight(_ text: String, color: UIColor) {
        guard let labelText = self.text else { return }
        let range = (labelText as NSString).range(of: text)

        let mutableAttributedString = NSMutableAttributedString.init(string: labelText)
        mutableAttributedString.addAttribute(NSAttributedString.Key.foregroundColor, value: color, range: range)
        self.attributedText = mutableAttributedString
    }

    func appendReadmore(after text: String, trailingContent: TrailingContent) {
        self.numberOfLines = minimumLines
        let fourLineText = "\n\n\n"
        let fourlineHeight = requiredHeight(for: fourLineText)
        let sentenceText = NSString(string: text)
        let sentenceRange = NSRange(location: 0, length: sentenceText.length)
        var truncatedSentence: NSString = sentenceText
        var endIndex: Int = sentenceRange.upperBound
        let size: CGSize = CGSize(width: self.bounds.width, height: CGFloat.greatestFiniteMagnitude)
        while truncatedSentence.boundingRect(with: size, options: .usesLineFragmentOrigin, attributes: attributes, context: nil).size.height >= fourlineHeight {
            if endIndex == 0 {
                break
            }
            endIndex -= 1

            truncatedSentence = NSString(string: sentenceText.substring(with: NSRange(location: 0, length: endIndex)))
            truncatedSentence = (String(truncatedSentence) + trailingContent.text) as NSString

        }
        self.text = truncatedSentence as String
        self.highlight(trailingContent.text, color: highlightColor)
    }

    func appendReadLess(after text: String, trailingContent: TrailingContent) {
        self.numberOfLines = 0
        self.text = text + trailingContent.text
        self.highlight(trailingContent.text, color: highlightColor)
    }
}

Hi,

You've to add a tap gesture to the label to catch the tap and an extension UITapGesture to know which part of the label has tapped.

Step 1: Enable UILabel user interaction.

textLabel.isUserInteractionEnabled = true

Step 2: Add Tap gesture to UILabel and set action

@IBAction func didTapLabel(_ sender: UITapGestureRecognizer) { }

Step 3: Add an extension UITapGestureRecognizer to identify which part of the label has tapped, readmore/readless.

extension UITapGestureRecognizer {

    func didTap(label: UILabel, inRange targetRange: NSRange) -> Bool {
        
        // Create instances of NSLayoutManager, NSTextContainer and NSTextStorage
        let layoutManager = NSLayoutManager()
        let textContainer = NSTextContainer(size: CGSize.zero)
        let textStorage = NSTextStorage(attributedString: label.attributedText!)

        // Configure layoutManager and textStorage
        layoutManager.addTextContainer(textContainer)
        textStorage.addLayoutManager(layoutManager)

        // Configure textContainer
        textContainer.lineFragmentPadding = 0.0
        textContainer.lineBreakMode = label.lineBreakMode
        textContainer.maximumNumberOfLines = label.numberOfLines
        let labelSize = label.bounds.size
        textContainer.size = labelSize

        // Find the tapped character location and compare it to the specified range
        let locationOfTouchInLabel = self.location(in: label)
        let textBoundingBox = layoutManager.usedRect(for: textContainer)

        let textContainerOffset = CGPoint(x: (labelSize.width - textBoundingBox.size.width) * 0.5 - textBoundingBox.origin.x, y: (labelSize.height - textBoundingBox.size.height) * 0.5 - textBoundingBox.origin.y)

        let locationOfTouchInTextContainer = CGPoint(x: locationOfTouchInLabel.x - textContainerOffset.x, y: locationOfTouchInLabel.y - textContainerOffset.y)
        let indexOfCharacter = layoutManager.characterIndex(for: locationOfTouchInTextContainer, in: textContainer, fractionOfDistanceBetweenInsertionPoints: nil)
        return NSLocationInRange(indexOfCharacter, targetRange)
    }

}

Step 4: Handle the readmore/readless in tap action

 @IBAction func didTapLabel(_ sender: UITapGestureRecognizer) {
        guard let text = textLabel.text else { return }

        let readmore = (text as NSString).range(of: TrailingContent.readmore.text)
        let readless = (text as NSString).range(of: TrailingContent.readless.text)
        if sender.didTap(label: textLabel, inRange: readmore) {
            textLabel.appendReadLess(after: textDescription, trailingContent: .readless)
        } else if  sender.didTap(label: textLabel, inRange: readless) {
            textLabel.appendReadmore(after: textDescription, trailingContent: .readmore)
        } else { return }
        
    }

Try this!

https://github.com/Catherine-K-George/Readmore-Readless.git