ShouldChangeTextInRange is not called for UITextView

I user custom UITextView and need to hide keyboard on return click. I need to catch 'ShouldChangeTextInRange' what has textview, I don't know why but method is not called. here is code of for my text view :

     public class PlaceholderTextView : UITextView
        { 
public PlaceholderTextView ()
        {
            Initialize ();
        }

        public PlaceholderTextView (CGRect frame)
            : base (frame)
        {
            Initialize ();
        }

        public PlaceholderTextView (IntPtr handle)
            : base (handle)
        {
            Initialize ();
        }

        void Initialize ()
        {
            Text = Placeholder;

            ShouldBeginEditing = t => {
                if (Text == Placeholder)
                    Text = string.Empty;

                return true;
            };

            ShouldEndEditing = t => {
                if (string.IsNullOrEmpty (Text))
                    Text = Placeholder;
                return true;
            };

        }
        public override bool ShouldChangeTextInRange (UITextRange inRange, string replacementText)
                {
                    if (Text.Equals ("\n")) {
                        this.EndEditing (true);
                        return false;
                    } else {
                        return true;
                    }
                }
        }