How to limit UITextField input to only accept numerical values?

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One way to limit UITextField input to only accept numerical values is by implementing the UITextFieldDelegate method shouldChangeCharactersIn range:. Here's an example implementation in Swift:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let allowedCharacters = CharacterSet.decimalDigits
    let characterSet = CharacterSet(charactersIn: string)
    return allowedCharacters.isSuperset(of: characterSet)
}

In this implementation, we define allowedCharacters as the set of decimal digits. Then, we check if the characterSet composed of the characters in string is a subset of allowedCharacters. If it is, we allow the change to occur, otherwise we block it.

Next, set the delegate property of your UITextField instance to the view controller that implements the above delegate method. Now, the UITextField will only allow numerical input.