Set the maximum character length of a UITextField in Swift

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 five characters.

Preferably alphanumeric, -, ., 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
}

How can I actually implement it? Which "textfield" should I swap out for my custom named UITextField?

Solution 1

1. Your view controller should conform to UITextFieldDelegate, like below:

   class MyViewController: UIViewController, UITextFieldDelegate {
   
   }
   

2. Set the delegate of your textfield: myTextField.delegate = self

3. Implement the method in your view controller:

   textField(_:shouldChangeCharactersInRange:replacementString:)
   

All together:

class MyViewController: UIViewController, UITextFieldDelegate  // Set delegate to class

@IBOutlet var mytextField: UITextField             //  textfield variable

override func viewDidLoad() {
    super.viewDidLoad()
    mytextField.delegate = self                  // set delegate
}


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
}

For Swift 4

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let maxLength = 1
    let currentString: NSString = (textField.text ?? "") as NSString
    let newString: NSString =  currentString.replacingCharacters(in: range, with: string) as NSString

    return newString.length <= maxLength
}

For Swift 5

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let maxLength = 1
    let currentString = (textField.text ?? "") as NSString
    let newString = currentString.replacingCharacters(in: range, with: string)

    return newString.count <= maxLength
}

Allowing only a specified set of characters to be entered into a given text field

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

    if mytextField == numberField {
        if count(string) > 0 {
            let disallowedCharacterSet = NSCharacterSet(charactersInString: "0123456789.-").invertedSet
            let replacementStringIsLegal = string.rangeOfCharacterFromSet(disallowedCharacterSet) == nil
            result = replacementStringIsLegal
        }
    }

    return result
}

How to program an iOS text field that takes only numeric input with a maximum length

Solution 2

Modern Swift

Note that much of the example code online regarding this problem is extremely 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).string
    }
}

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 )

---

For the OCD programmer (like me)...

As @LeoDabus reminds, .prefix returns a substring. If you're incredibly caring, this

let t = textField.text
textField.text = t?.prefix(maxLength)

would be

if let t: String = textField.text {
    textField.text = String(t.prefix(maxLength))
}

Enjoy!

Solution 3

In Swift 4, simply use:

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

Solution 4

The same way Steven Schmatz did it but using Swift 3.0 :

//max Length
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange,
               replacementString string: String) -> Bool
{
    let maxLength = 4
    let currentString: NSString = textField.text! as NSString
    let newString: NSString = currentString.replacingCharacters(in: range, with: string) as NSString
    return newString.length <= maxLength
}

Solution 5

For Swift 5:

Just write one line to set the maximum character length:

 self.textField.maxLength = 10

For more details, see Max character limit of UITextField and allowed characters Swift. (Also credited.)

View more solutions

Comments

[Leo Dabus]

Swift 4 implementation stackoverflow.com/a/46513151/2303865

[Fattie]

Quick alert - to shorten a String in Swift these days you can finally just .prefix(n)

[ishkur88]

Thank you so much for the prompt reply! If I set this one textfield as the delegate would I be able to modify other textfields?

[Alaeddine]

yes, and you will get the textfield in question (being edited ) as the first parameter textField in the method func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool

[ishkur88]

But where would I put in the second parameter? I don't reference myTextField again after I set it as a delegate.

[ishkur88]

Like if I wanted to make another textfield 0-9 only for phone numbers.

[Alaeddine]

every time a textfield is being edited, the callback shouldChangeCharactersInRange is called, this is for all textfields, you receive the callback in the same place shouldChangeCharactersInRange and inside this method you can know which textfield is being edited thanks to the passed parameter textField you can for example give a tag for each textfield and test inside the shouldChangeCharactersInRange and for each textfield perform the validation of the content

[Alaeddine]

@ishkur88 I have updated the answer with another example note the if mytextField == numberField { to check the textField that is being edited

[Theo Bendixson]

Does this particular solution allow the user to enter a backspace character once the user has hit the character limit? Would we need a way to let backspaces through?

[J. Doe]

Seems legit! Thank you.

[mylovemhz]

That all this has to be done to achieve something so common and so simple blows my mind. They couldn't just give us a simple textField.maxLength built-in...anyway your solution is great, thanks!

[jonathan3087]

Wow, best tip I have ever had on SO. I'd up vote it 100 if I could!

[Alan Scarpa]

For Swift 4, this self.characters is deprecated. It is now just let c = self

[Vamshi Krishna]

Cannot we do something like this for regex validation (like phoneNumber, emailId, userName)?

[Angel G. Olloqui]

The solution is handy but the map of textfields at the top will actually produce a retain cycle.

[Fattie]

hi @AngelGarcíaOlloqui - it's an excellent point, in the unusual case where they're not just from storyboards, you'd have to attend to that. Good thinking!

[Keyhan Kamangar]

Thanks for your answer, Can u explain maxLengths please?

[Ankur Lahiry]

The answer I am looking for :D

[user832]

this should be the selected answer. Simple and workes well.

[Slavcho]

It doesnt work. What if you tap in the middle of the string and you can type more than X chars.

[Leo Dabus]

super.didMoveToSuperview() "The default implementation of this method does nothing. Subclasses can override it to perform additional actions whenever the superview changes." Considering it calling super for that method is pointless

[Fattie]

an excellent point @LeoDabus , thanks! I'll leave it there to help new programmers with the typical pattern; Happy new year!

[Leo Dabus]

@Fattie you are welcome. Happy new year for you too.

[Fattie]

@TheoBendixson , the more modern solution of simply using . editingChanged completely handles all such issues.

[cornr]

This does not handle copy and paste

[Saqib Saud]

instead of range.location < 10, you can use textField.text.length < 10. This solution is simple and elegant.

[10623169]

This should be the accepted answer. Works perfectly, with no bugs.

[zeeshan]

This is the solution, simple and elegant, with no boilerplate code.

[ViruMax]

This solution creates a new issue while typing in other languages like Mandarin, Korean, etc.

[Hasya]

Good answer. Appreciated.

[juancazalla]

WARNING FOR THOSE USING THIS SOLUTION! This solution has some problems. One of them is that if the user types at the beginning of the textField, you are going to allow them to type the new character and the last one will be removed, also, the cursor will jump to the last character in the field. Another problem is that if you set the text programmatically, it will allow you to set a text bigger than the limit. Another problem occurs if you undo a change (CMD+Z with an external keyboard) it will crash if you tried to add a digit over the limit previously.

[Fattie]

hi @juancazalla ! the first three are desired behaviors, and depend on what you or the client wants. regarding the external keyboard undo issue, that's a great point, I did not think of testing with an external keyboard! I will try to repo that!

[Sachin Rana]

Suppose I have 2 textfields. Both require different max char limit, one require 10 char and other require 20 char. In that case what approach should I need to follow. Is there any way to make maxLength variable dynamic?

[Сергей Билык]

You can use this solution: if textField.text?.count >= 12 { return false }

[Reza Dehnavi]

it doesn't work when past a text if you want to work in past action you should add string.count < MAX_LENGTH

[iDev]

This cannot work. Location is not the length of the string but the position of the cursor / selelction.

[Dylan]

it gives me an error saying Expression type '()' is ambiguous without more context on prefix

[Dylan]

hi @Fattie I posted my question here stackoverflow.com/q/62165247/6800631

[Leo Dabus]

@Fattie you need to update the post textField.text = String(textField.text!.prefix(maxLength)) and text = String(text!.prefix(4))

[Leo Dabus]

Prefix returns a substring

[Leo Dabus]

I think since String started conforming to RangeReplaceableCollection

[Leo Dabus]

@Fattie You can safely force unwrap it. Its default value is an empty String. It will NEVER return nil. You can even set it to nil and it wont return nil after that.

[Fattie]

hi @LeoDabus , you know, I wonder if that assumption in the specific UITextField class would confuse newer users; it's not something one can assume generally ... :O

[Leo Dabus]

You can warn them about this case being an exception :) As well as the reason why there is no need to call super.didMoveToSuperview()

[Leo Dabus]

The text property being optional allows you to assign an optional string to it without the need to unwrap its value

[FontFamily]

While this solution may seem straightforward, there is actually a lot more code that is required to implement this. This answer isn't very helpful by itself and the addition of an explanation and inclusion of other relevant pieces of code might be helpful.

[Silvering]

Best answer. Thanks

[deepOcean]

Worked in my case, only digits in textfield

[Peter Mortensen]

Isn't something missing from the source code near "class MyViewController"? The syntax highlighting is off.

[Peter Mortensen]

There is no one here by the name "Steven Schmatz". What answer does it refer to? Is it SwiftMatt's answer? The other three possibilities are "Alaeddine", "ZaEeM ZaFaR", and "Cloy" (deleted answer - link-only answer).

[Peter Mortensen]

There is no one here by the name "Frouo". What answer does it refer to?

[Peter Mortensen]

Will that work? MAX_LENGHT looks like a misspelling. Why isn't it MAX_LENGTH? Where is it defined? Dictionary: length

[Peter Mortensen]

What is meant by the last sentence? Can you elaborate? What is not checked? What is only checked? For example, do you mean "Here I only checked for characters allowed in textField"? Please respond by editing (changing) your answer, not here in comments (without "Edit:", "Update:", or similar - the answer should appear as if it was written today).

[TD540]

Defined nowhere :) I think his intention is for the reader of his comment to replace it with the wanted maximum length. Besides that, this answer should be the solution.