How Shouldchangecharactersinrange Works in Swift

How shouldChangeCharactersInRange works in Swift?

Swift 4, Swift 5

This method doesn't use NSString

// MARK: - UITextFieldDelegate

extension MyViewController: UITextFieldDelegate {
    func textField(_ textField: UITextField,
                   shouldChangeCharactersIn range: NSRange,
                   replacementString string: String) -> Bool {
        if let text = textField.text,
           let textRange = Range(range, in: text) {
           let updatedText = text.replacingCharacters(in: textRange,
                                                       with: string)
           myvalidator(text: updatedText)
        }
        return true
    }
}

Note. Be careful when you use a secured text field.

Textfield shouldchangecharactersinrange swift

You could use a target on your textField with the control event EditingChanged instead of the delegate method.

Swift >= 1.0

myTextField.addTarget(self, action: "didChangeText:", forControlEvents: .EditingChanged)

Swift 3.0 (String literal selectors are deprecated, use #selector)

myTextField.addTarget(self, action: #selector(didChangeText(_:)), for: .editingChanged)

Then use the targeted method to run your checks.

func didChangeText(textField:UITextField) {
    if textField.text == "apple" {
        checkImageView1.hidden = false
    } else {
        checkImageView1.hidden = true
    }
}

UITextView shouldChangeCharactersInRange in Swift

Requires UITextViewDelegate reference in class line:

class MyViewController: UIViewController, UITextViewDelegate {

}

AND it also requires a referencing outlet from the view controller to the textView delegate. Select the view controller, click on outlets, drag from referencing outlet to the textView, click delegate.

Using `textField:shouldChangeCharactersInRange:`, how do I get the text including the current typed character?

-shouldChangeCharactersInRange gets called before text field actually changes its text, that's why you're getting old text value. To get the text after update use:

[textField2 setText:[textField1.text stringByReplacingCharactersInRange:range withString:string]];

UITextField shouldChangeCharactersInRange doesn't detect first character

The shouldChangeCharactersInRange() function is asking whether the change should be applied but it has not yet allowed your textfield to be modified.

func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool
{
  if textField == myTextField {
    let textString : NSString = textField.text!
    let candidateString : NSString = textString.stringByReplacingCharactersInRange(range, withString: string)    
    let updatedTextString : NSString = PartialFormatter().formatPartial(candidateString as String)
    print(updatedTextString)
    textField.text = updatedTextString
  }
  return true
} 

textField shouldChangeCharactersInRange is executing one step behind user action

The text hasn't changed yet when this method is called. You have to userange and replacementString to construct the email address, and then verify that.

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