Allows you to set the text in a UITextField *without* changing the position of the cursor.

UITextField+Extensions.swift

//
//  UITextField+Extensions.swift
//
//  Created by Daniel Tartaglia on 8/8/16.
//  Copyright © 2016 MIT License.
//

import UIKit


extension UITextField {

    func setText(to newText: String, preservingCursor: Bool) {
        if preservingCursor {
            let cursorPosition = offset(from: beginningOfDocument, to: selectedTextRange!.start) + newText.characters.count - (text?.characters.count ?? 0)
            text = newText
            if let newPosition = position(from: beginningOfDocument, offset: cursorPosition) {
                selectedTextRange = textRange(from: newPosition, to: newPosition)
            }
        }
        else {
            text = newText
        }
    }
}