Swift Form Validation - Check if Int or String has been entered

Question

I am trying to validate a form to make sure the user has entered an integer number and not a string. I can check if the number is an integer as follows:

 var possibleNumber = timeRetrieved.text
    convertedNumber = possibleNumber.toInt()
    // convertedNumber is inferred to be of type "Int?", or "optional Int"

    if convertedNumber != nil {

        println("It's a number!")

        totalTime = convertedNumber!


    }

My problem is I want to make sure the user has not entered any text, doubles etc. I only want integer numbers. The following code does not work because it evaluates true if the variable is an integer. What code should I use to evaluate if variable is not an integer?

if convertedNumber != nil  {


        let alertController = UIAlertController(title: "Validation Error", message: "You must enter an integer number!", preferredStyle: .Alert)
        let alertAction = UIAlertAction(title: "OK", style: UIAlertActionStyle.Destructive, handler: {(alert : UIAlertAction!) in
            alertController.dismissViewControllerAnimated(true, completion: nil)
        })
        alertController.addAction(alertAction)
        presentViewController(alertController, animated: true, completion: nil)

score 5 · Answer 1 · answered Jan 28 '16 at 17:45

Swift 2 changes this: as both Int("abc") and Int("0") return 0, integer conversion can't be used. You could use this:

class Validation {
    static func isStringNumerical(string : String) -> Bool {
        // Only allow numbers. Look for anything not a number.
        let range = string.rangeOfCharacterFromSet(NSCharacterSet.decimalDigitCharacterSet().invertedSet)
        return (range == nil)
    }
}

It uses a decimalDigitCharacterSet, and can be changed to use whatever character set you want.

func testIsStringNumerical() {
    XCTAssertEqual(SignUpLoyaltyViewController.isStringNumerical("123"), true)
    XCTAssertEqual(SignUpLoyaltyViewController.isStringNumerical(""), true)
    XCTAssertEqual(SignUpLoyaltyViewController.isStringNumerical("12AA"), false)
    XCTAssertEqual(SignUpLoyaltyViewController.isStringNumerical("123.4"), false)
}

This is dramatically faster than the Regex answer. (2000 runs, 0.004s vs regex 0.233s)

I am not sure when this changed but in Swift 2.2, `Int("abc")` and `Int("0")` return `nil`. I gleaned this from Minhal Khan's answer. I posted an answer which also uses this initializer. — Mobile Dan, Apr 07 '16 at 20:57

score 4 · Accepted Answer · answered Dec 04 '14 at 21:51

4

If the number the user has entered is not an integer, convertedNumber will be nil. Just add an else clause in which you can show the alert.

answered Dec 04 '14 at 21:51

Marnix999L

81
3

Thanks, I couldn't get my code to work until I put my convertToInt() function within my validate function. – Tom Dec 04 '14 at 22:45

Mobile Dan · Answer 3 · 2017-10-06T16:19:38.590

`Int` initializer

This works in Swift 2.2 and above. It is based on Minhal Khan's answer which illustrates that Int has an initializer with this signature: init?(_ text: String, radix: Int = default). Since radix has a default value, it can be left out. *more info on this initializer is found here.

var totalTime: Int?
let possibleInt = timeRetrieved.text ?? ""
if let convertedNumber = Int(possibleInt) {
    print("'\(possibleInt)' is an Int")
    totalTime = convertedNumber
}
else {
    print("'\(possibleInt)' is not an Int")
}

print("totalTime: '\(totalTime)'")

Note: I assumed timeRetrieved is a UITextField. The UITextField text property is an optional string (though programmatically not allowed to be nil). Therefore, the compiler requires it be unwrapped. I used the nil coalescing operator (??) to substitute a nil for empty string which does not yield an integer as desired. Here's a post that discusses the optionality of UITextfield.text.

score 1 · Answer 4 · answered Apr 02 '16 at 20:20

1

What i had done was get the value and check if it could convert it, works for me

var enteredText = Int(textfield.text) 
if enteredText == nil{
    //String entered 
} 
else{
//Int entered
}

answered Apr 02 '16 at 20:20

Minhal Khan

301
3
11

score 1 · Answer 5 · answered Sep 20 '16 at 08:23

Based on @Graham Perks answer a Swift 3 Version as string extension:

extension String
{
    var isNumeric: Bool
    {
        let range = self.rangeOfCharacter(from: CharacterSet.decimalDigits.inverted)
        return (range == nil)
    }
}

Usage:

"123".isNumeric // true
"abc".isNumeric // false

score 0 · Answer 6 · answered Jan 15 '16 at 18:38

I really recommend using a REGEX, I was recently trying to validate 10 digit phone numbers using if let _ = Int(stringToTest)... and on 32 bit hardware, I faced range issues.

func validate(value: String) -> Bool {
  let PHONE_REGEX = "\\d{10}"
  let phoneTest = NSPredicate(format: "SELF MATCHES %@", PHONE_REGEX)
  let result =  phoneTest.evaluateWithObject(value)
  if result == true {
    log.info("'\(self.text!)' is a valid number.")
  } else {
    log.info("'\(self.text!)' is an invalid number.")
  }
  return result
}

Swift Form Validation - Check if Int or String has been entered

6 Answers6

Int initializer

`Int` initializer