Set the maximum character length of a UITextField

Question

I know there are other topics on this but I can't seem to find out how to implement it.

I'm trying to limit a UITextField to only 5 Characters

Preferably Alphanumeric and - and . and _

I've seen this code

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange,
                       replacementString string: String) -> Bool
{
    let maxLength = 4
    let currentString: NSString = textField.text
    let newString: NSString =
             currentString.stringByReplacingCharactersInRange(range, withString: string)
    return newString.length <= maxLength
}

and

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {

    let length = count(textField.text.utf16) + count(string.utf16) - range.length
    return length <= 10 
}

I just don't know how to actually implement it or which "textfield" should I swap out for my custom named UITextField

Answer 1

Other solutions posted above produce a retain cycle due to the textfield map. Besides, the maxLength property should be nullable if not set instead of artificial Int.max constructions; and the target will be set multiple times if maxLength is changed.

Here an updated solution for Swift4 with a weak map to prevent memory leaks and the other fixes

private var maxLengths = NSMapTable<UITextField, NSNumber>(keyOptions: NSPointerFunctions.Options.weakMemory, valueOptions: NSPointerFunctions.Options.strongMemory)

extension UITextField {

    var maxLength: Int? {
        get {
            return maxLengths.object(forKey: self)?.intValue
        }
        set {
            removeTarget(self, action: #selector(limitLength), for: .editingChanged)
            if let newValue = newValue {
                maxLengths.setObject(NSNumber(value: newValue), forKey: self)
                addTarget(self, action: #selector(limitLength), for: .editingChanged)
            } else {
                maxLengths.removeObject(forKey: self)
            }
        }
    }

    @IBInspectable var maxLengthInspectable: Int {
        get {
            return maxLength ?? Int.max
        }
        set {
            maxLength = newValue
        }
    }

    @objc private func limitLength(_ textField: UITextField) {
        guard let maxLength = maxLength, let prospectiveText = textField.text, prospectiveText.count > maxLength else {
            return
        }
        let selection = selectedTextRange
        text = String(prospectiveText[..<prospectiveText.index(from: maxLength)])
        selectedTextRange = selection
    }
}

Answer 2

Just in case, don't forget to guard range size before applying it to the string. Otherwise, you will get crash if the user will do this:

Type maximum length text Insert something (Nothing will be inserted due to length limitation, but iOS doesn't know about it) Undo insertion (You get crash, cause range will be greater than actual string size)

Also, using iOS 13 users can accidentally trigger this by gestures

I suggest you add to your project this

extension String {
    func replace(with text: String, in range: NSRange) -> String? {
        guard range.location + range.length <= self.count else { return nil }
        return (self as NSString).replacingCharacters(in: range, with: text)
    }
}

And use it like this:

func textView(_ textView: UITextView, shouldChangeTextIn range: NSRange, replacementText text: String) -> Bool {
    guard let newText = textView.text.replace(with: text, in: range) else { return false }
    return newText.count < maxNumberOfCharacters
}

Otherwise, you will constantly be getting crashed in your app

Answer 3

Dec 2017. Swift 4.

Take care that much of the example code which you will see online regarding this problem is very out of date.

Paste the following into any Swift file in your project. You can name the file anything, for example, "Handy.swift"

This finally fixes one of the stupidest problems in iOS:

Your text fields now have a .maxLength.

It is completely OK to set that value in storyboard during development, or, set it in code while the app is running.

// simply have this in any Swift file, say, Handy.swift

import UIKit
private var __maxLengths = [UITextField: Int]()
extension UITextField {
    @IBInspectable var maxLength: Int {
        get {
            guard let l = __maxLengths[self] else {
               return 150 // (global default-limit. or just, Int.max)
            }
            return l
        }
        set {
            __maxLengths[self] = newValue
            addTarget(self, action: #selector(fix), for: .editingChanged)
        }
    }
    func fix(textField: UITextField) {
        let t = textField.text
        textField.text = t?.prefix(maxLength)
    }
}

It's that simple.

---

Footnote - these days to safely truncate a String in swift, you simply .prefix(n)

---

An even simpler one-off version...

The above fixes all text fields in your project.

If you just want one particular text field to simply be limited to say "4", and that's that...

class PinCodeEntry: UITextField {

    override func didMoveToSuperview() {

        super.didMoveToSuperview()
        addTarget(self, action: #selector(fixMe), for: .editingChanged)
    }

    @objc private func fixMe() { text = text?.prefix(4) }
}

Phew! That's all there is to it.

(Just BTW, here's a similar very useful tip relating to UITextView, https://stackoverflow.com/a/42333832/294884 )

Answer 4

I think extension is more handy for this. See full answer here

private var maxLengths = [UITextField: Int]()

// 2
extension UITextField {

  // 3
  @IBInspectable var maxLength: Int {
    get {
      // 4
      guard let length = maxLengths[self] else {
        return Int.max
      }
      return length
    }
    set {
      maxLengths[self] = newValue
      // 5
      addTarget(
        self,
        action: #selector(limitLength),
        forControlEvents: UIControlEvents.EditingChanged
      )
    }
  }

  func limitLength(textField: UITextField) {
    // 6
    guard let prospectiveText = textField.text
      where prospectiveText.characters.count > maxLength else {
        return
    }

    let selection = selectedTextRange
    // 7
    text = prospectiveText.substringWithRange(
      Range<String.Index>(prospectiveText.startIndex ..< prospectiveText.startIndex.advancedBy(maxLength))
    )
    selectedTextRange = selection
  }

}

Answer 5

I have something to add to Aladin's answer:

1. Your view controller should conform to UITextFieldDelegate

   class MyViewController: UIViewController, UITextViewDelegate {
   
   }
   

2. Set the delegate of your textfield: To set the delegate, you can control drag from the textfield to your view controller in the storyboard. I think this is preferable to setting it in code

3. Implement the method in your view controller : textField(_:shouldChangeCharactersInRange:replacementString:)

Answer 6

Swift 4, simply use:

public func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    return range.location < 10
}