Convert to uppercase even when pasted text in the textfield.

autoUppercasingTextField.swift

import UIKit

public class AutoUpperCasingTextField: UITextField, UITextFieldDelegate {
    
    // Max char to limit.
    var maxNumber: Int = 0 {
        didSet {
            self.delegate = self
        }
    }
    
    // Flag to convert every input text to Uppercase
    var autoUppercasing = false
    
    public func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        guard let textFieldText = self.text,
            let rangeOfTextToReplace = Range(range, in: textFieldText) else {
                return false
        }
        
        // Char limitation process
        let substringToReplace = textFieldText[rangeOfTextToReplace]
        let count = textFieldText.count - substringToReplace.count + string.count
        guard count <= self.maxNumber else {
            return false
        }
        
        // Stop right there for limitation only.
        if autoUppercasing == false {
            return true
        }
        
        // Uppercasing process
        let lowercaseCharacters = NSCharacterSet.lowercaseLetters
        if string.rangeOfCharacter(from: lowercaseCharacters) != nil {
            let uppercaseString = string.uppercased()
            
            guard let inputText = textField.text else {
                return false
            }
            
            if inputText.isEmpty {
                // Updates return button; forces cursor to the end
                textField.text = (inputText as NSString).replacingCharacters(in: range, with: uppercaseString)
            } else {
                // Preserves cursor location; doesn't update return button
                let beginning = textField.beginningOfDocument
                guard let start = textField.position(from: beginning, offset: range.location) else {
                    return false
                }
                guard let end = textField.position(from: start, offset: range.length) else {
                    return false
                }
                guard let range = textField.textRange(from: start, to: end) else {
                    return false
                }
                textField.replace(range, withText: uppercaseString)
            }
            return false
        } else {
            return true
        }
    }
}

preventPasteAction.swift

// Prevent paste action in UITextField.
class PaymentInfoExpireTextField: UITextField {

    // Diable paste function in credit card expire date textfields.
    override func canPerformAction(_ action: Selector, withSender sender: Any?) -> Bool {
        if action == #selector(UIResponderStandardEditActions.paste(_:)) {
            return false
        }
        return super.canPerformAction(action, withSender: sender)
    }
}

Swift