[Swift] Detect Touches on Attributed Text in UILabel

It’s always funny when you google “how do I…” and Google shows you a result that you actually wrote.

I wanted to solve this problem, and it looks like I did it years ago in Objective-C.

So, I re-wrote it in Swift that you can basically just copy-paste-use.  You’re welcome.

//
//  TappableLabel.swift
//
//  Created by Stephen O'Connor on 07.10.20.
//  MIT License.  You will send no lawyers here.  Have fun.
//  taken from here:  https://horseshoe7.wordpress.com/2015/12/10/detect-touches-on-attributed-text-in-uilabel/

import UIKit

typealias LabelLink = (text: String, link: Any?)

protocol TappableLabelDelegate: class {
    func didTapOnLink(_ link: LabelLink, in tappableLabel: TappableLabel)
}

extension NSAttributedString.Key {
    static let custom = NSAttributedString.Key("CustomAttribute")
}

class TappableLabel: UILabel {
    
    weak var delegate: TappableLabelDelegate?
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
    }
    
    override func awakeFromNib() {
        super.awakeFromNib()
        commonInit()
    }
    
    private func commonInit() {
        self.textAlignment = .left // has to be left for this to work!
        addGestureRecognizers()
    }
    
    private func addGestureRecognizers() {
        let tap = UITapGestureRecognizer(target: self, action: #selector(tappedLabel(_:)))
        self.isUserInteractionEnabled = true
        self.addGestureRecognizer(tap)
        
    }
    
    @objc
    private func tappedLabel(_ tap: UITapGestureRecognizer) {
        guard let label = tap.view as? TappableLabel, label == self, tap.state == .ended else {
            return
        }
        let location = tap.location(in: label)
        processInteraction(at: location, wasTap: true)
    }
    private func processInteraction(at location: CGPoint, wasTap: Bool) {
        
        let label = self
        
        guard let attributedText = label.attributedText else {
            return // nothing to do
        }
        
        let textStorage = NSTextStorage(attributedString: attributedText)
        let textContainer = NSTextContainer(size: label.bounds.size)
        let layoutManager = NSLayoutManager()
        layoutManager.addTextContainer(textContainer)
        textStorage.addLayoutManager(layoutManager)
        
        textContainer.lineFragmentPadding = 0.0
        textContainer.lineBreakMode = label.lineBreakMode
        textContainer.maximumNumberOfLines = label.numberOfLines
        
        
        let characterIndex = layoutManager.characterIndex(for: location,
                                                          in: textContainer,
                                                          fractionOfDistanceBetweenInsertionPoints: nil)
        if characterIndex < textStorage.length {
            log.info("Character Index: \(characterIndex)")
            let range = NSRange(location: characterIndex, length: 1)
            let substring = (attributedText.string as NSString).substring(with: range)
            
            log.info("Character at Index: \(substring)")
            if let labelLink = attributedText.attribute(.custom,
                                                        at: characterIndex,
                                                        effectiveRange: nil) as? LabelLink {
                
                log.debug("You \(wasTap ? "tapped" : "pressed") on \(labelLink.text) and the value is: \(String(describing: labelLink.link))")
                self.delegate?.didTapOnLink(labelLink, in: self)
            }
        }
    }
    
    // will set the label's text to the given text argument, but for any callbackString it will search the text for that and embed it.
    func setText(_ text: String, withCallbacksOn callbackStrings: [LabelLink] = []) {
        
        self.text = text
        
        let attributedString = NSMutableAttributedString(string: text)
        let coreAttributes: [NSAttributedString.Key: Any] = [
            .foregroundColor : self.textColor!,
            .font: self.font!
        ]
        attributedString.setAttributes(coreAttributes,
                                       range: NSRange(location: 0, length: text.count))
        
        for labelLink in callbackStrings {
            
            let range = (text as NSString).range(of: labelLink.text)
            if range.location != NSNotFound {
                var additionalAttributes = coreAttributes
                additionalAttributes[.custom] = labelLink
                attributedString.setAttributes(additionalAttributes, range: range)
            }
        }
        self.attributedText = attributedString
    }
}

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