Restrict NSTextField to only allow numbers

Question

How do I restrict a NSTextfield to allow only numbers/integers? I\'ve found questions like this one, but they didn\'t help!

Answer 1

In SWIFT, I do it this way

1. Convert the text value to Int with Int()
2. Check the converted value is not less than 0

3. If less than 0, display error message other accept the value

   if ((Int(txtField.stringValue)) < 0){
       // Display error message
   }