How do I get the value of a UITextfield as characters are being typed in real time?

Question

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 :

let acceptedChars = NSCharacterSet(charactersInString: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_")

now how do i capture a specific textfield in real time and track its input?

Answer 1

Try this:

 func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool {
        let invalidCharacters = NSCharacterSet(charactersInString: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_").invertedSet
        if let range = string.rangeOfCharacterFromSet(invalidCharacters, options: nil, range:Range<String.Index>(start: string.startIndex, end: string.endIndex)) {
            return false
        }

        return true
    }

Answer 2

You can register your textField for value change event like this

textfield.addTarget(self, action:"textFieldDidChange", forControlEvents:UIControlEvents.EditingChanged)

func textFieldDidChange(){
    // put your code
}

It will work for each chracter you have been typed in real time

Answer 3

var strings: NSString?

class ViewController: UIViewController,UITextFieldDelegate //set your textfield delegate

 func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool
{  if(textField .isEqual(your textfield))
    {
    strings=string;
    let acceptedChars = NSCharacterSet(charactersInString: "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890_").invertedSet;

     if (strings!.rangeOfCharacterFromSet(acceptedChars.invertedSet).location != NSNotFound)
    {
        return true;
    }
    else
    {
        return false;
    }        
}
else
{
return true;
}
}

Answer 4

use below method

   func textField(textField: UITextField, shouldChangeCharactersInRange range: NSRange, replacementString string: String) -> Bool
    {
        if textField.isEqual(<textField whose value to be copied>)
        {
            <TextField to be updated>.text = (textField.text as NSString).stringByReplacingCharactersInRange(range, withString: string)
        }
    
        return true
    }

Answer 5

An Easy Delegate method and really more efficient is:

func textFieldDidChangeSelection(_ textField: UITextField) {
    print(textField.text)
}