protected void btnNew_Click(object sender, EventArgs e)
        {
            string username = txtUsername.Text.Trim();

            if (username.Equals(""))
            {
                lblMessage.Text      = "Username cannot be empty!";
                lblMessage.ForeColor = Color.Red;
                return;
            }
            string password = txtPassword.Text.Trim();

            if (password.Equals(""))
            {
                lblMessage.Text      = "Password cannot be empty!";
                lblMessage.ForeColor = Color.Red;
                return;
            }
            string firstname = txtFirstname.Text.Trim();
            string lastname  = txtLastname.Text.Trim();
            string phone     = txtPhone.Text.Trim();
            double phoneNum  = 0;

            try
            {
                phoneNum = double.Parse(phone);
            }
            catch
            {
                lblMessage.Text      = "Phone number not valid!";
                lblMessage.ForeColor = Color.Red;
            }
            string email = txtEmail.Text.Trim();

            if (!IsEmailValid(email))
            {
                lblMessage.Text      = "Email is not valid!";
                lblMessage.ForeColor = Color.Red;
                return;
            }
            StaffDTO dto = new StaffDTO
            {
                Username  = username,
                Password  = password,
                FirstName = firstname,
                LastName  = lastname,
                Phone     = phone,
                Email     = email,
                IsActive  = true
            };

            try
            {
                if (dao.AddNewStaff(username, password, firstname, lastname, phone, email, true))
                {
                    lblMessage.Text      = "Successfully added";
                    lblMessage.ForeColor = Color.Green;
                }
                else
                {
                    lblMessage.Text      = "Failed to add";
                    lblMessage.ForeColor = Color.Red;
                }
            }
            catch
            {
                lblMessage.Text      = "Username is already existed, please choose another one";
                lblMessage.ForeColor = Color.Red;
            }
        }