How shouldChangeCharactersInRange works in Swift?

Question

I\'m using shouldChangeCharactersInRange as a way of using on-the-fly type search.

However I\'m having a problem, shouldChangeCharactersInRange get

Answer 1

To get the exact text in the my UITextField component in Swift 3.0 I used:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
   let enteredTxt = textField.text! + string
   doSomethingWithTxt(enteredTxt) //some custom method
}

Answer 2

This function is called when changes are made but UI is not updated and waiting for your choice

Take a look at returned bool value

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool

• If you return true - it means that iOS accept changes(text, caret...)
• If you return false - it means that you are responsible for all this stuff

Answer 3

Swift 3

---

If you want to pre-process the characters the user typed or pasted, the following solution workes like a charm

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

    let strippedString = <change replacements string so it fits your requirement - strip, trim, etc>

    // replace current content with stripped content
    if let replaceStart = textField.position(from: textField.beginningOfDocument, offset: range.location),
        let replaceEnd = textField.position(from: replaceStart, offset: range.length),
        let textRange = textField.textRange(from: replaceStart, to: replaceEnd) {

        textField.replace(textRange, withText: strippedString)
    }
    return false
}

Find it here: https://gist.github.com/Blackjacx/2198d86442ec9b9b05c0801f4e392047

Answer 4

stringByReplacingCharactersInRange return a new string, so how about:

func textField(textField: UITextField!, shouldChangeCharactersInRange range: NSRange, replacementString string: String!) -> Bool {
    if let text = textField.text as NSString? {
        let txtAfterUpdate = text.replacingCharacters(in: range, with: string)
        self.callMyMethod(txtAfterUpdate)
    }
    return true
}

Answer 5

Swift 3 & 4

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let textFieldText: NSString = (textField.text ?? "") as NSString
    let txtAfterUpdate = textFieldText.replacingCharacters(in: range, with: string)
    callMyMethod(txtAfterUpdate)

    return true
}

func textFieldShouldClear(_ textField: UITextField) -> Bool {
    callMyMethod("")
    return true
}

Swift 2.2

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
    let textFieldText: NSString = textField.text ?? ""
    let txtAfterUpdate = textFieldText.stringByReplacingCharactersInRange(range, withString: string)
    callMyMethod(txtAfterUpdate)

    return true
}

func textFieldShouldClear(textField: UITextField) -> Bool {
    callMyMethod("")
    return true
}

Though the textField.text property is an optional, it cannot be set to nil. Setting it to nil is changed to empty string within UITextField. In the code above, that is why textFieldText is set to empty string if textField.text is nil (via the nil coalescing operator ??).

Implementing textFieldShouldClear(_:) handles the case where the text field's clear button is visible and tapped.

Answer 6

In Swift 3 it would look like this:

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    let text: NSString = (textField.text ?? "") as NSString
    let resultString = text.replacingCharacters(in: range, with: string)

    return true
}