text changed event in UITextView

I have

@IBOutlet weak var messageTextView: UITextView

and I want that when there is a change inside the text then print to console: blabla.

I tried to add the following function, but when I change the text nothing happens:

func textViewDidChange(_ textView: UITextView) {
    switch (textView) {
        case messageTextView: print("blabla")
        default: break
    }
}