为什么我的组合框数据绑定不起作用？

我正在创建一个简单的发票应用程序，它从表单中获取一些细节并创建PDF文件 . 数据存储在SQL Server数据库中 .

问题在于客户选择组合框控件，其中显示的项目在选择时不显示正确的客户信息 . 第一项显示数据库中最后一条记录的详细信息，反之亦然 .

有问题的控件：

Customer 表：

表单加载时的数据绑定， IMSDBAccess 是一个处理数据库查询的类：

private void InvoiceDetails_Load(object sender, EventArgs e)
    {
        txtBillingAddress.DataBindings.Add("Text", IMSDBAccess.queryDB("SELECT streetaddress FROM Customer"), "streetaddress");
        txtPostcode.DataBindings.Add("Text", IMSDBAccess.queryDB("SELECT postzip FROM Customer"), "postzip");
        txtCity.DataBindings.Add("Text", IMSDBAccess.queryDB("SELECT towncity FROM Customer"), "towncity");
        txtState.DataBindings.Add("Text", IMSDBAccess.queryDB("SELECT stateprovince FROM Customer"), "stateprovince");
        txtCountry.DataBindings.Add("Text", IMSDBAccess.queryDB("SELECT country FROM Customer"), "country");

        cboCustomer.DataSource = IMSDBAccess.queryDB("SELECT customerNo, (RTRIM(business_name) + ' (' + CONVERT(varchar(10), customerNo) + ')') AS DisplayValue FROM Customer");
        cboCustomer.BindingContext = this.BindingContext;
        cboCustomer.DisplayMember = "DisplayValue";
        cboCustomer.ValueMember = "customerNo";
    }

当组合框中所选项目发生变化时：

private void cboCustomer_SelectedIndexChanged(object sender, EventArgs e)
    {
        updateCustomer();
    }

Combobox更新方法：

private void updateCustomer()
    {
        MessageBox.Show(cboCustomer.SelectedValue.ToString());
        int cNo;
        bool parseOK = Int32.TryParse(cboCustomer.SelectedValue.ToString(), out cNo);
        string query = "SELECT * FROM Customer WHERE customerNo = @customerNo";

        SqlConnection connectionObj = new SqlConnection(IMSDBAccess.GetConnectionString(""));
        SqlCommand cmd = new SqlCommand(query, connectionObj);
        SqlDataReader reader;

        cmd.Parameters.AddWithValue("@customerNo", cNo);

        try
        {
            connectionObj.Open();
            reader = cmd.ExecuteReader();

            if (reader.Read())
            {
                txtBillingAddress.Text = reader["streetaddress"].ToString();
                txtCity.Text = reader["towncity"].ToString();
                txtState.Text = reader["stateprovince"].ToString();
                txtCountry.Text = reader["country"].ToString();
                txtPostcode.Text = reader["postzip"].ToString();
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message, "Error updating customer info", MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1);
        }
    }

我无法理解如何以正确的顺序绑定数据，以便cboCustomer中的项目对应于文本框中显示的数据 .