Avoid UITextView alignment bug. https://stackoverflow.com/questions/26524431/uitextview-alignment-caret-goes-left

CenteredTextView.swift

import UIKit

class CenteredTextView: UITextView {
    override init(frame: CGRect, textContainer: NSTextContainer?) {
        super.init(frame: frame, textContainer: textContainer)
        setup()
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        setup()
    }

    override func prepareForInterfaceBuilder() {
        super.prepareForInterfaceBuilder()
        setup()
    }

    private func setup() {
        textAlignment = .center

        // Avoid the bug of the text align changed to the left.
        NotificationCenter.default.addObserver(forName: UITextView.textDidChangeNotification, object: self, queue: .main) { [weak self] (_) in
            guard self?.textAlignment != .center else { return }
            self?.textAlignment = .center
        }
    }

    // Avoid the bug of the caret position changed to the left.
    override func caretRect(for position: UITextPosition) -> CGRect {
        let caretRect = super.caretRect(for: position)
        let rangeOfCaret = NSRange(location: selectedRange.location + selectedRange.length, length: 0)
        let rangeOfCharBeforeCaret = NSRange(location: rangeOfCaret.location > 0 ? rangeOfCaret.location - 1 : 0, length: 1)
        let rangeOfCharAfterCaret = NSRange(location: rangeOfCaret.location, length: 1)
        let fullRange = NSRange(location: 0, length: text.count)
        
        // \n Added in the middle of String
        let isMiddleOfString = NSLocationInRange(rangeOfCharBeforeCaret.location, fullRange) &&
            NSLocationInRange(NSMaxRange(rangeOfCharAfterCaret), fullRange) &&
            text.substring(with: rangeOfCharBeforeCaret) == "\n" &&
            text.substring(with: rangeOfCharAfterCaret) == "\n"
        // \n Added in the end of String
        let isEndOfString = NSMaxRange(rangeOfCharAfterCaret) >= NSMaxRange(fullRange) &&
            text.substring(with: rangeOfCharBeforeCaret) == "\n"
        
        if isMiddleOfString || isEndOfString {
            // Newline before and after the caret. Make it centered.
            let correction = bounds.midX - caretRect.midX
            let centeredCaretRect = caretRect.offsetBy(dx: correction, dy: 0)
            return centeredCaretRect
        }
        else {
            return caretRect
        }
    }
}

fileprivate extension String {
    func substring(with nsrange: NSRange) -> Substring? {
        guard let range = Range(nsrange, in: self) else { return nil }
        return self[range]
    }
}