How to detect touch on NSTextAttachment

Question

What is the best way to detect when user taps on NSTextAttachment on iOS?

I think that one of the ways would be checking for the character on carret\'s

Answer 1

I have altered Drew's gesture recognizer here to subclass UITapGestureRecognizer rather than UIGestureRecognizer.

This offers one advantage in that it only detects discrete taps as opposed to the beginning of a scroll.

import UIKit
import UIKit.UIGestureRecognizerSubclass

// Modified from: https://stackoverflow.com/a/49153247/658604

/// Recognizes a tap on an attachment, on a UITextView.
/// The UITextView normally only informs its delegate of a tap on an attachment if the text view is not editable, or a long tap is used.
/// If you want an editable text view, where you can short cap an attachment, you have a problem.
/// This gesture recognizer can be added to the text view, and will add requirments in order to recognize before any built-in recognizers.
class AttachmentTapGestureRecognizer: UITapGestureRecognizer {

    typealias TappedAttachment = (attachment: NSTextAttachment, characterIndex: Int)

    private(set) var tappedState: TappedAttachment?

    override func touchesBegan(_ touches: Set, with event: UIEvent) {
        tappedState = nil

        guard let textView = view as? UITextView else {
            state = .failed
            return
        }

        if let touch = touches.first {
            tappedState = evaluateTouch(touch, on: textView)
        }

        if tappedState != nil {
            // UITapGestureRecognizer can accurately differentiate discrete taps from scrolling
            // Therefore, let the super view evaluate the correct state.
            super.touchesBegan(touches, with: event)

        } else {
            // User didn't initiate a touch (tap or otherwise) on an attachment.
            // Force the gesture to fail.
            state = .failed
        }
    }

    /// Tests to see if the user has tapped on a text attachment in the target text view.
    private func evaluateTouch(_ touch: UITouch, on textView: UITextView) -> TappedAttachment? {
        let point = touch.location(in: textView)
        let glyphIndex: Int? = textView.layoutManager.glyphIndex(for: point, in: textView.textContainer, fractionOfDistanceThroughGlyph: nil)
        let index: Int? = textView.layoutManager.characterIndexForGlyph(at: glyphIndex ?? 0)
        guard let characterIndex = index, characterIndex < textView.textStorage.length else {
            return nil
        }
        guard NSTextAttachment.character == (textView.textStorage.string as NSString).character(at: characterIndex) else {
            return nil
        }
        guard let attachment = textView.textStorage.attribute(.attachment, at: characterIndex, effectiveRange: nil) as? NSTextAttachment else {
            return nil
        }
        return (attachment, characterIndex)
    }
}