Swift - How can I force users to import only integer in UITextField?

Question

Normally, in Text Field, users can enter a String, and even if the users entered a number, the program would automatically understand it as a string.

So, here is my problem. I want to make a program evaluating the speed of a motorcyclist.

I have a text field, a text view and a button START. What I want to do is to apply SWITCH - CASE in classifying the number that the users enter in the text field, and then I will print out my evaluations to the text view, such as "Slow", "Fast Enough" or "Dangerously Fast".

However before applying switch - case, I think that I have to force the users to only enter Integer numbers to the text field. And if they enter any alphabet letter, the text view will appear: "Wrong format! Please try again!"

I think that I have to do something with the statement if to solve the problem, but the truth is I've just started learning Swift, and couldnt think of any possible solutions. Please help me. Thank you.

Answer 1

If you are using storyboard just select the TextField and change the Keyboard type to NumberPad. This will only allow integers to be entered. Then you could just turn it into a Int when you get back the input.

   if let convertedSpeed = Int(textField.text) {
        // Implement whatever you want
   } else {
        // Notify user of incorrect input
   }

Answer 2

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool
    {
        if textField == Number_Txt // your text filed name
        {
            var result = true
            let prospectiveText = (textField.text! as NSString).stringByReplacingCharactersInRange(range, withString: string)

            if string.characters.count > 0
            {
                let disallowedCharacterSet = NSCharacterSet(charactersInString: "0123456789").invertedSet
                let replacementStringIsLegal = string.rangeOfCharacterFromSet(disallowedCharacterSet) == nil

                let resultingStringLengthIsLegal = prospectiveText.characters.count > 0 

                let scanner = NSScanner(string: prospectiveText)
                let resultingTextIsNumeric = scanner.scanDecimal(nil) && scanner.atEnd

                result = replacementStringIsLegal && resultingStringLengthIsLegal && resultingTextIsNumeric
            }
            return result
        }
        else
        {
            return true
        }
    }

Answer 3

You can specify the keyboard type of a textfield in storyboard, under attributes inspector. "Decimal" would be the way to go for you (assuming that possible input can be e.g. 180.5)

To move on, you still can check the input like this:

if (Int(textfield.text!) != nil ) {
     //Valid number, do stuff
} else {
    textfield.text = "Wrong format! Please try again!"
}

EDIT:

The ' != nil ' means the following:

The Initializer of Int is failable. That means if you pass a string which does not contain a valid number, it will return nil (null if you are coming from java/c#). But if the string does contain a valid number, it will return a valid Int, therefore its not nil. I hope this makes it clear to you ;)

Answer 4

You can solve it in two ways.

1. Convert the typed text to Integer value.

   Int(textfield.text!)

2. This one is very simpler. Choose the keyboard type as Numeric/ Numbers and Punctuation pad. So that, user can type only the nos.

Hope it helps..