textbox validation

Add an event handler for KeyPress for the TextBox and use following code:

        private void txtBx_KeyPress(object sender, KeyPressEventArgs e)
        {
            if (e.KeyChar == '\b'                       // Allowing Back Space
                ||Char.IsLetterOrDigit(e.KeyChar)       // Allowing any letter OR Digit
                    || e.KeyChar == '-')                // Allowing Hyphen
            {
                e.Handled = false;
            }
            else
            {
                e.Handled = true;
            }
        }