Trying to limit maxTextFieldLength

Question

I am writing an application which needs inputs of volumes and prices, I want to limit the volume to a 4 digit number, and the price to a 4 digit number with a decimal in place between the 4 digits.

How do I go about encoding this into my project?

I have searched multiple pages and found this: (http://www.globalnerdy.com/2016/05/24/a-better-way-to-program-ios-text-fields-that-have-maximum-lengths-and-accept-or-reject-specific-characters/) I still keep getting an error towards the end of my code for the TextFieldMaxLength.Swift file.

@objc func limitLength(textField: UITextField) {
    guard let prospectiveText = textField.text, prospectiveText.count > maxLength else {
            return
    }

    // If the change in the text field's contents will exceed its maximum length,
    // allow only the first [maxLength] characters of the resulting text.
    let selection = selectedTextRange
    text = prospectiveText.substringWith(
        Range<String.Index>(prospectiveText.startIndex ..< prospectiveText(maxLength))
    )
    selectedTextRange = selection
}

I am expecting to be able to limit the individual textFields to different numbers. In the interface building there is a section that can be entered to limit this. But this error keeps popping up: "Cannot call value of non-function type String", in the section which depicts:

text = prospectiveText.substringWith(
            Range<String.Index>(prospectiveText.startIndex ..< prospectiveText(maxLength))
        )

Answer 1

What you should do is implement the UITextFieldDelegate method textField(_:shouldChangeCharactersIn:replacementString:).

This delegate method is called before the text updates within the UITextField. Within it, you can check the length of the current string, and return false if the current length is 4 characters and the added character isn't a backspace, and true otherwise. Similarly, you can change the textField's text and return false, effectively processing the updating character, and returning the appropriate string.

I've created a github repository that I used to test this code here: Github Repository

First, be sure that you set the Keyboard Type of both UITextFields to Number Pad in the interface builder.

Next, add the following extension to the string class.

extension String {
    func stringByRemovingAll(characters: [Character]) -> String {
        var stringToReturn = self
        for character in characters {
            stringToReturn = stringToReturn.replacingOccurrences(of: String(character), with: "")
        }
        return stringToReturn
    }

    subscript (i: Int) -> Character {
        return self[index(startIndex, offsetBy: i)]
    }
}

And now, actually addressing the issue:

import UIKit

class ViewController: UIViewController {

    @IBOutlet var volumeTextField: UITextField!
    @IBOutlet var priceTextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        volumeTextField.delegate = self
        priceTextField.delegate = self
    }
}


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

        //An empty string, i.e. "", is the passed text when the user enters a backspace
        if textField == volumeTextField {

            if textField.text!.count == 4 && string != "" {
                return false
            } else {
                return true
            }
        } else {

            let currentText = textField.text!.stringByRemovingAll(characters: ["$","."])
            print(currentText)

            var newText: String!
            if string == "" {
                newText = String(currentText.dropLast())
            } else if currentText.count == 0 {
                newText = string
            } else {
                newText = "\(currentText)\(string)"
            }


            while newText.count != 0 && newText[0] == "0" {
                newText.remove(at: newText.startIndex)
            }

            switch newText.count {

            case 0:
                textField.text = "$00.00"
            case 1:
                textField.text = "$00.0\(newText!)"

            case 2:
                textField.text = "$00.\(newText[0])\(newText[1])"

            case 3:
                textField.text = "$0\(newText[0]).\(newText[1])\(newText[2])"

            case 4:
                textField.text = "$\(newText[0])\(newText[1]).\(newText[2])\(newText[3])"

            default:
                break
            }
            return false
        }
    }
}

Within this delegate method, you can also put a check on the character passed, and return false if it isn't one of the few characters you want allowed.

End result:

Reference: Apple docs textField(_:shouldChangeCharactersIn:replacementString:) reference