public void Delete()
        {
            using (var s = new NSMutableString(0)) {
                s.SetString((NSString)"Hello World");
                s.DeleteCharacters(new NSRange(5, 6));
                Assert.That(s.ToString(), Is.EqualTo("Hello"), "deleetd");

                Assert.Throws <ArgumentOutOfRangeException> (delegate {
                    s.DeleteCharacters(new NSRange(0, s.Length + 1));
                }, "bad 1");

                Assert.Throws <ArgumentOutOfRangeException> (delegate {
                    s.DeleteCharacters(new NSRange(1, s.Length));
                }, "bad 2");
            }
        }
    public override void Changed(UITextView textView)
    {
        Console.WriteLine("-----" + secureText);
        if (secureTextViewEntry)
        {
            string text = textView.Text;
            if (text.Length > 0)
            {
                if ("" == lastText)
                {
                    secureText.DeleteCharacters(new NSRange(secureText.Length - 1, 1));
                    onlyPassword();
                    timer.Invalidate();
                    //base.Changed(textView);
                    return;
                }
                else
                {
                    NSString one = new NSString(text.Substring(text.Length - 1));
                    secureText.Append(one);
                    NSMutableString temp = new NSMutableString();
                    for (int i = 0; i < secureText.Length - 1; i++)
                    {
                        temp.Append(new NSString("•"));
                    }
                    temp.Append(new NSString(secureText.ToString().Substring(secureText.ToString().Length - 1)));
                    myTextView.Text = temp;

                    //timer.Invalidate();
                    timer = NSTimer.CreateScheduledTimer(2, onlyPassword);
                }
            }
            else
            {
                secureText = new NSMutableString();
            }
            //base.Changed(textView);
        }
        else
        {
            if (textView.Text.Length == 0)
            {
                secureText = new NSMutableString();
            }
            else
            {
                secureText = new NSMutableString();
                secureText.SetString(new NSString(textView.Text));
            }

            timer.Invalidate();
            //base.Changed(textView);
        }
    }