private void btnAddStaff_Click(object sender, EventArgs e)
        {
            if (txtFirstName.isEmptyOrHint())
            {
                txtFirstName.Focus();
                return;
            }
            if (txtLastName.isEmptyOrHint())
            {
                txtLastName.Focus();
                return;
            }
            if (txtAddress1.isEmptyOrHint())
            {
                txtAddress1.Focus();
                return;
            }
            if (txtAddress2.isEmptyOrHint())
            {
                txtAddress2.Focus();
                return;
            }

            if (txtCity.isEmptyOrHint())
            {
                txtCity.Focus();
                return;
            }

            if (txtCountry.isEmptyOrHint())
            {
                txtCountry.Focus();
                return;
            }

            if (txtPostalCode.isEmptyOrHint())
            {
                txtPostalCode.Focus();
                return;
            }

            if (txtPhoneNumber.isEmptyOrHint())
            {
                txtPhoneNumber.Focus();
                return;
            }
            if (txtQualification.isEmptyOrHint())
            {
                txtQualification.Focus();
                return;
            }
            Staff newStaff = new Staff()
            {
                FirstName     = txtFirstName.Text.Trim(),
                LastName      = txtLastName.Text.Trim(),
                Address1      = txtAddress1.Text.Trim(),
                Address2      = txtAddress2.Text.Trim(),
                City          = txtCity.Text.Trim(),
                Country       = txtCountry.Text.Trim(),
                PostalCode    = txtPostalCode.Text.Trim(),
                PhoneNumber   = txtPhoneNumber.Text.Trim(),
                Qualification = txtQualification.Text.Trim(),
                Password      = txtPassword.Text.Trim(),
                Username      = txtUsername.Text.Trim(),
            };

            if (_isUpdate)
            {
                if (_updatedStaff == null)
                {
                    MessageBox.Show("Error in system!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                    return;
                }

                newStaff.Id = _updatedStaff.Id;
                int res = _sr.UpdateStaff(newStaff);

                if (res < 0)
                {
                    MessageBox.Show("Error In Update!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                else
                {
                    ActionPerformed?.Invoke(newStaff, ActionType.Updated);
                    Hide();
                }
            }
            else
            {
                int res = _sr.AddStaffMember(newStaff);
                if (res < 0)
                {
                    MessageBox.Show("Error In Adding New Staff!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
                else
                {
                    newStaff.Id = res;
                    ActionPerformed?.Invoke(newStaff, ActionType.Added);
                    Hide();
                }
            }
            Clear();
        }