Using stringByReplacingCharactersInRange in Swift

I created an extension to NSRange the converted to Range<String.Index>

extension NSRange { func toRange(string: String) -> Range<String.Index> { let startIndex = advance(string.startIndex, location) let endIndex = advance(startIndex, length) return startIndex..<endIndex } } 

So I can create the String like this

let text = textField.text let newText = text.stringByReplacingCharactersInRange(range.toRange(text), withString: string) 

in Swift 2.1 the extension looks like:

extension NSRange { func toRange(string: String) -> Range<String.Index> { let startIndex = string.startIndex.advancedBy(location) let endIndex = startIndex.advancedBy(length) return startIndex..<endIndex } } 

The simplest solution I have found is using as NSString - that enables us to use NSRange.

var textField : UITextField = UITextField() textField.text = "this is a test" let nsRange : NSRange = NSRange(location: 0, length: 4) let replaced = (textField.text as NSString) .stringByReplacingCharactersInRange(nsRange, withString: "that"); NSLog("Replaced: %@", replaced); //prints "that is a test" 

let newString = (textField.text as NSString).stringByReplacingCharactersInRange(range, withString: string) 

bridgeToObjectiveC can be removed in coming updates

Nothing worked for me except the following: (FYI I'm using Xcode7.0 GM, Swift 2.0, iOS9GM)

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool { let currentText = textField.text ?? "" let prospectiveText = (currentText as NSString).stringByReplacingCharactersInRange(range, withString: string) print("prospectiveText", prospectiveText) return true; } 

As of Swift 4, this is a little simpler, like Alexander Volkov's answer, but without the extension.

 func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool { let revisedText: String if let text = textField.text, let swiftRange = Range(range, in: text) { revisedText = text.replacingCharacters(in: swiftRange, with: string) } else { revisedText = string } // Do something with the text and return boolean. } 

This is a cross-post from this question, but without a way to make a Range<String.Index> the Swift-native String.stringByReplacingCharactersInRange() is pretty useless. So, here's a function to generate a Range<String.Index>:

func RangeMake(#start:Int, #end:Int) -> Range<String.Index> { assert(start <= end, "start must be less than or equal to end") func rep(str: String, count: Int) -> String { var result = "" for i in 0..count { result += str } return result } let length = end - start let padding = rep(" ", start) let dashes = rep("-", length) let search = padding + dashes return search.rangeOfString(dashes, options: nil, range: Range(start: search.startIndex, end: search.endIndex), locale: NSLocale.systemLocale()) } let sourceString = "Call me Ishmael." let range = RangeMake(start: 8, end: 15) let name = sourceString.substringWithRange(range) // name = "Ishmael" 

Working & tested

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool { let newString = NSString(string: textField.text!).replacingCharacters(in: range, with: string) print(newString) return true; } 

Creating String.Index is cumbersome.

let string = "hello" let range = string.startIndex .. string.startIndex.succ().succ() let result = string.stringByReplacingCharactersInRange(range, withString: "si") 

for iOS 8.3 use following code

 func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool { if textField.isEqual(<textField whose value to be copied>) { <TextField to be updated>.text = (textField.text as NSString).stringByReplacingCharactersInRange(range, withString: string) } return true } 

With Swift 2.0, the answer from Durul must be changed because characters.count must be used instead of count().

The following must be done.

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool { let length = textField.text!.characters.count - range.length + string.characters.count if length > 0 { submitButton.enabled = true } else { submitButton.enabled = false } return true } 

import UIKit class LoginViewController: UIViewController, UITextFieldDelegate { @IBOutlet weak var submitButton: UIButton! override func viewDidLoad() { super.viewDidLoad() // Do any additional setup after loading the view. } override func didReceiveMemoryWarning() { super.didReceiveMemoryWarning() // Dispose of any resources that can be recreated. } func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool { let length = count(textField.text) - range.length + count(string) if length > 0 { submitButton.enabled = true } else { submitButton.enabled = false } return true } } 

Swift 4:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool { var text = textField.text ?? "" text.replaceSubrange(range.toRange(string: text), with: string) ... return true } extension NSRange { /// Convert to Range for given string /// /// - Parameter string: the string /// - Returns: range func toRange(string: String) -> Range<String.Index> { let range = string.index(string.startIndex, offsetBy: self.lowerBound)..<string.index(string.startIndex, offsetBy: self.upperBound) return range } }