UITextInput.characterRange(at:) is off by a few pixels - ios

Question

After adding a tap recognizer to my UITextView subclass, I'm attempting to get the character that is being tapped:
var textRecognizer: UITapGestureRecognizer!
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
textContainer.lineFragmentPadding = 0
textContainerInset = .zero
textRecognizer = UITapGestureRecognizer(target: self, action: #selector(textTapped))
textRecognizer.numberOfTapsRequired = 1
addGestureRecognizer(textRecognizer)
}
#objc func textTapped(recognizer: UITapGestureRecognizer) {
let location = recognizer.location(in: self)
if let cRange = characterRange(at: location) {
let cPosition = offset(from: beginningOfDocument, to: cRange.start)
let cChar = text[Range(NSRange(location: cPosition, length: 1), in: text)!]
print(cChar)
}
}
Problem is that if my attributedText is "Hello world\nWelcome to Stack Overflow" and I tap on the left part of a letter, like the left side of letter f, then characterRange(at: location) returns the previous letter r instead of returning f.

Answer 1

From my perspective, characterRange(at:) is buggy:
If you give it a point on the left half of character at index n, it returns range (n-1, n)
If you give it a point on the right half of character at index n, it returns range (n, n+1)
If you give it a point on the left half of character at index beginningOfDocument, it returns nil
If you give it a point on the right half of character at index endOfDocument, it returns (endOfDocument, endOfDocument+1)
The discrepancy of the behaviors at the extremities of the textInput demonstrate that there is a bug somewhere.
It behaves like a sort of "cursor position at point" function, which makes it unreliable to determine which character is actually at this point: is it the character before the cursor or the character after the cursor?
closestPosition(to:) suffers from the exact same issue.
A working alternative is layoutManager.characterIndex(for:in:fractionOfDistanceBetweenInsertionPoints:). Credit to vacawama:
#objc func textTapped(recognizer: UITapGestureRecognizer) {
var location = recognizer.location(in: self)
location.x -= textContainerInset.left
location.y -= textContainerInset.top
let cPosition = layoutManager.characterIndex(for: location, in: textContainer, fractionOfDistanceBetweenInsertionPoints: nil)
let cChar = text[Range(NSRange(location: cPosition, length: 1), in: text)!]
print(cChar)
}