How to limit the textfield entry to 2 decimal places in swift 4?

Only Two decimal point allow and only one "." allow

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

                    let text: NSString = textField.text! as NSString
                    let resultString = text.replacingCharacters(in: range, with: string)


        //Check the specific textField 
         if textField == costTextField {
             let textArray = resultString.components(separatedBy: ".")
             if textArray.count > 2 { //Allow only one "."
                return false
             }
           if textArray.count == 2 {
              let lastString = textArray.last
             if lastString!.count > 2 { //Check number of decimal places 
                   return false
               }
            }
          }
           return true
       }

Set your controller as the delegate for the text field and check if the proposed string satisfy your requirements:

override func viewDidLoad() {
    super.viewDidLoad()
    textField.delegate = self
    textField.keyboardType = .decimalPad
}

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    guard let oldText = textField.text, let r = Range(range, in: oldText) else {
        return true
    }

    let newText = oldText.replacingCharacters(in: r, with: string)
    let isNumeric = newText.isEmpty || (Double(newText) != nil)
    let numberOfDots = newText.components(separatedBy: ".").count - 1

    let numberOfDecimalDigits: Int
    if let dotIndex = newText.index(of: ".") {
        numberOfDecimalDigits = newText.distance(from: dotIndex, to: newText.endIndex) - 1
    } else {
        numberOfDecimalDigits = 0
    }

    return isNumeric && numberOfDots <= 1 && numberOfDecimalDigits <= 2
}

In Swift 4.

TextField have 10 digit limit and after decimal 2 digit limit (you can change the Limits). The dot will allow only one time in the textField.

class ViewController: UIViewController,UITextFieldDelegate {

    var dotLocation = Int()

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


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

        if Int(range.length) == 0 && string.count == 0 {
            return true
        }

        if (string == ".") {
            if Int(range.location) == 0 {
                return false
            }
            if dotLocation == 0 {
                dotLocation = range.location
                return true
            } else {
                return false
            }
        }

        if range.location == dotLocation && string.count == 0 {
            dotLocation = 0
        }

        if dotLocation > 0 && range.location > dotLocation + 2 {
            return false
        }

        if range.location >= 10 {

            if dotLocation >= 10 || string.count == 0 {
                return true
            } else if range.location > dotLocation + 2 {
                return false
            }

            var newValue = (textField.text as NSString?)?.replacingCharacters(in: range, with: string)
            newValue = newValue?.components(separatedBy: nonNumberSet).joined(separator: "")
            textField.text = newValue

            return false

        } else {
            return true
        }

    }

}

Guys, here's the solution:

 func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        let dotString = "."

        if let text = textField.text {
            let isDeleteKey = string.isEmpty

            if !isDeleteKey {
                if text.contains(dotString) {
                    if text.components(separatedBy: dotString)[1].count == 2 {

                                return false

                    }

                }

            }
        }
  }