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

Question

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.

Answer 1

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
}