title: How do I get the value of a UITextfield as characters are being typed in real time?
body: <p>I am attempting to regulate the input of a UITextfield in real time, meaning as a user is typing. I have this character set that i need to compare to the input string, and while editing if an unwarranted character is typed in, I want to relay an alert. Here is my character set :</p>
  
  <p><code>let acceptedChars = NSCharacterSet(charactersInString: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_")</code> </p>
  
  <p>now how do i capture a specific textfield in real time and track its input? </p>