Swift. Format input in textField - ios

Question

I created textField and want to format text in it like 43/35. Number / number - for credit card month and year.
Can I use number fomatter for it or how can I do it more easily?
The issue here that I need to replace 3rd character if I add new character and remove it if I remove 2nd one.
I do not want use any 3rd party library, I need native implementation

Answer 1

This is my current solution. Basically you need to:
1) Implement the delegate of your textfield somewhere (in my code below I implemented on the ViewController)
2) Implement textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool.
To apply the mask, I created some extensions for String and Characters, as you can see at the end of the following code:
class ViewController: UIViewController {
#IBOutlet weak var textfield: UITextField!
let mask = "##/##"
override func viewDidLoad() {
super.viewDidLoad()
textfield.delegate = self
}
}
extension ViewController: UITextFieldDelegate {
func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
guard let normalText = textField.text else { return false }
let beginning = textField.beginningOfDocument
// save cursor location
let cursorLocation = textField.positionFromPosition(beginning, offset: range.location + string.characters.count)
let newString = (normalText as NSString).stringByReplacingCharactersInRange(range, withString: string)
let newStringClean = newString.stringWithOnlyNumbers().withMask(mask)
guard newString != newStringClean else { return true }
textField.text = newStringClean
guard string != "" else { return false }
// fix cursor location after changing textfield.text
if let cL = cursorLocation {
let textRange = textField.textRangeFromPosition(cL, toPosition: cL)
textField.selectedTextRange = textRange
}
return false
}
}
extension String {
func stringWithOnlyNumbers() -> String {
return self.characters.reduce("") { (acc, c) -> String in
guard c.isDigit() else { return acc }
return "\(acc)\(c)"
}
}
func withMask(mask: String) -> String {
var resultString = String()
let chars = self.characters
let maskChars = mask.characters
var stringIndex = chars.startIndex
var maskIndex = mask.startIndex
while stringIndex < chars.endIndex && maskIndex < maskChars.endIndex {
if (maskChars[maskIndex] == "#") {
resultString.append(chars[stringIndex])
stringIndex = stringIndex.successor()
} else {
resultString.append(maskChars[maskIndex])
}
maskIndex = maskIndex.successor()
}
return resultString
}
}
extension Character {
func isDigit() -> Bool {
let s = String(self).unicodeScalars
let uni = s[s.startIndex]
let digits = NSCharacterSet.decimalDigitCharacterSet()
let isADigit = digits.longCharacterIsMember(uni.value)
return isADigit
}
}

Answer 2

Swift 4:
extension CodeEnterViewController: UITextFieldDelegate {
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
guard let normalText = textField.text else { return false }
let beginning = textField.beginningOfDocument
// save cursor location
let cursorLocation = textField.position(from: beginning, offset: range.location + string.count)
let newString = (normalText as NSString).replacingCharacters(in: range, with: string)
let newStringClean = newString.stringWithOnlyNumbers().withMask(mask: mask)
guard newString != newStringClean else { return true }
textField.text = newStringClean
guard string != "" else { return false }
// fix cursor location after changing textfield.text
if let cL = cursorLocation {
let textRange = textField.textRange(from: cL, to: cL)
textField.selectedTextRange = textRange
}
return false
}
}
String
extension String {
func stringWithOnlyNumbers() -> String {
return self.reduce("") { (acc, c) -> String in
guard c.isDigit() else { return acc }
return "\(acc)\(c)"
}
}
func withMask(mask: String) -> String {
var resultString = String()
let chars = self
let maskChars = mask
var stringIndex = chars.startIndex
var maskIndex = mask.startIndex
while stringIndex < chars.endIndex && maskIndex < maskChars.endIndex {
if (maskChars[maskIndex] == "#") {
resultString.append(chars[stringIndex])
stringIndex = chars.index(after: stringIndex)
} else {
resultString.append(maskChars[maskIndex])
}
maskIndex = chars.index(after: maskIndex)
}
return resultString
}
}
Character
extension Character {
func isDigit() -> Bool {
let s = String(self).unicodeScalars
let uni = s[s.startIndex]
let digits = NSCharacterSet.decimalDigits
let isADigit = digits.hasMember(inPlane: UInt8(uni.value))
return isADigit
} }