Swift Text Field (IOS, Xcode 7.3, Swift 2): User keys in 4 digits. how to limit input to numeric and limit the number of digits to exactly 4

Question

App requires User to input 4 digits into a Text Field. How do you limit it to just 4? and how to limit to Numeric?

Answer 1

here is a code snippet --> don't forget set a delegate on UITextField

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    let nonNumberSet = NSCharacterSet.decimalDigitCharacterSet().invertedSet
    if (string.stringByTrimmingCharactersInSet(nonNumberSet).characters.count > 0 && textField.text?.characters.count < 4) || (string.characters.count == 0 && range.length > 0) {
        return true
    }
    return false
}