How can I declare that a text field can only contain an integer?

Question

In swift, I am trying to make a text field that will allow a button to be enabled, but only when the text field contains an integer. How can I do this?

Answer 1

Each text field has a keyboardType. You could set this to UIKeyboardType.NumbersAndPunctuation to only show numbers and still have the return key present (defensive UI). You could then use NSScanner's scanInt() to check if textField.text is a valid integer.

Answer 2

You can use NSScanner to do that here is the which might be useful trying using this and let me know if there are any issues

if( [[NSScanner scannerWithString:@"-123.4e5"] scanFloat:NULL] )
    NSLog( @"\"-123.4e5\" is numeric" );
else
    NSLog( @"\"-123.4e5\" is not numeric" );

if( [[NSScanner scannerWithString:@"Not a number"] scanFloat:NULL] )
    NSLog( @"\"Not a number\" is numeric" );
else
    NSLog( @"\"Not a number\" is not numeric" );

go through the link http://rosettacode.org/wiki/Determine_if_a_string_is_numeric#Objective-C. Try it in swift the class and method names are same.

Answer 3

1st you have to inherit the UITextViewDelegate class with you own class

class ViewController: UIViewController, UITextViewDelegate {

2nd add an IBOutlet

@IBOutlet weak var firstName: UITextField!

3rd you have to assure this object is using

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


func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    if textField == firstName {
                let allowedCharacters = "1234567890"
                let allowedCharacterSet = CharacterSet(charactersIn: allowedCharacters)
                let typedCharacterSet = CharacterSet(charactersIn: string)
                let alphabet = allowedCharacterSet.isSuperset(of: typedCharacterSet)
              return alphabet



      }
  }