How to prevent "0" as the first character and limit number of characters allowed in UITextField using Swift?

user_4441676 0
Viewed 4274

I want to achieve following:

  1. Have a decimal keypad. Which means user will be able to enter Double values. (Needless to say "." will be limited one)
  2. Prevent "0" characters as the first characters. (i.e.: There should not be values like "003" "01" "000012" etc.)
  3. Limit the character count to 10.
  4. Only allow numbers. No Copy-Paste text values.

I am using decimal keypad. Below code handles first and third item above:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let currentString: NSString = (textField.text ?? "") as NSString
    let newString = currentString.replacingCharacters(in: range, with: string)
    return newString.count <= 10
}

Thank you for your time.

swift uikeyboard uitextfield ios
3 Answers

Bellow code will check all conditions you have specified

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    
    
    //Prevent "0" characters as the first characters. (i.e.: There should not be values like "003" "01" "000012" etc.)
    if textField.text?.count == 0 && string == "0" {
        
        return false
    }
    
    //Limit the character count to 10.
    if ((textField.text!) + string).count > 10 {
        
        return false
    }
    
    //Have a decimal keypad. Which means user will be able to enter Double values. (Needless to say "." will be limited one)
    if (textField.text?.contains("."))! && string == "." {
        
        return false
    }

    //Only allow numbers. No Copy-Paste text values.
    let allowedCharacterSet = CharacterSet.init(charactersIn: "0123456789.")
    let textCharacterSet = CharacterSet.init(charactersIn: textField.text! + string)
    if !allowedCharacterSet.isSuperset(of: textCharacterSet) {
        return false
    }
    return true
}
user_46724780

You can use regex that define a number with <= 10 digits and not starting with 0, then use NSPredicate or NSRegularExpression to validate the entered text. Something like this:

func isAllowed(str: String?) -> Bool {
    let regexPattern: String = "^((?!(0))[0-9]{0,10})$"
    let predicate = NSPredicate(format:"SELF MATCHES %@", regexPattern)

    return predicate.evaluate(with: str)
}

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    return isAllowed(str: textField.text)
}
user_14558160

You can Create this method to prevent from copy paste 

override func canPerformAction(action: Selector, withSender sender: AnyObject?) -> Bool {
        if action == "paste:" {
            return false
        }        
        return super.canPerformAction(action, withSender: sender)
    }

and also you can add the following code to shouldChangeCharactersInRange Delegate method of textfield 

  let searchString = (txtMobilePhone.text as NSString?)?.replacingCharacters(in: range, with: string)

        if (searchString?.length)! > 1 {

            let inverseSet = CharacterSet(charactersIn: ".0123456789").inverted

            return ((string as NSString).rangeOfCharacter(from: inverseSet).location == NSNotFound)

        } else {

            let inverseSet = CharacterSet(charactersIn: ".123456789").inverted

            return ((string as NSString).rangeOfCharacter(from: inverseSet).location == NSNotFound)
        }

this above will only allow the user to enter the "0" after the second character I mean restricts the user to type "0" at the starting of numbers

user_86086500
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