UITextViewの文字数制御

textView.swift

    /// 文字数制御
    /// refs: https://akaimo.hatenablog.jp/entry/2015/09/13/150241
    func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
        self.previousText = textView.text
        self.lastReplaceRange = range
        self.lastReplacementString = text
        return true
    }

    func textViewDidChange(_ textView: UITextView) {
        guard textView.markedTextRange == nil else { return }
        guard textView.text.count > messageMaxCount else {
            return
        }

        let offset = messageMaxCount - textView.text.count
        let replacementString = lastReplacementString[..<lastReplacementString.index(lastReplacementString.endIndex, offsetBy: offset)]
        let text = previousText.replacingCharacters(in: Range(lastReplaceRange, in: previousText)!, with: String(replacementString))
        if let range = textView.selectedTextRange, let position = textView.position(from: range.start, offset: offset) {
            let selectedTextRange = textView.textRange(from: position, to: position)
            textView.text = text
            textView.selectedTextRange = selectedTextRange
        }
    }