UITextField Value Changed Event?

How can I make it so that when the contents of a text field changes, a function is called?

Objective-C

[myTextField addTarget:self 
                action:@selector(textFieldDidChange:) 
      forControlEvents:UIControlEventEditingChanged];

Swift 4

myTextField.addTarget(self, action: #selector(textFieldDidChange(sender:)), for: .editingChanged)

@objc func textFieldDidChange(sender: UITextField) {...}

Actually, there is no value changed event for UITextField, use UIControlEventEditingChanged

I resolved the issue changing the behavior of shouldChangeChractersInRange. If you return NO the changes won't be applied by iOS internally, instead you have the opportunity to change it manually and perform any actions after the changes.

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string {
    //Replace the string manually in the textbox
    textField.text = [textField.text stringByReplacingCharactersInRange:range withString:string];
    //perform any logic here now that you are sure the textbox text has changed
    [self didChangeTextInTextField:textField];
    return NO; //this make iOS not to perform any action
}

this is my solution.

Swift 4

textField.addTarget(self, action: #selector(self.textFieldDidChange(sender:)), for: .editingChanged)

@objc func textFieldDidChange(sender: UITextField){
   print("textFieldDidChange is called")
}

For swift this comes handy -

textField.addTarget(self, action: #selector(onTextChange), forControlEvents: UIControlEvents.EditingChanged)