Question

我目前正在使用ASP.Net Webforms开发一个系统，我在我的一个页面上有这个代码：

namespace mypms.View
{
    public partial class Reports : System.Web.UI.Page
    {
        private string truck_id = null;

        MySqlConnection conn = new MySqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);

        protected void Page_Load(object sender, EventArgs e)
        {

            truck_id = this.Request.QueryString["u"] != null ? this.Request.QueryString["u"] : Session["truck_id"] != null ? Session["truck_id"].ToString() : "";
            connectDB();
        }

        private void connectDB()
        {
            try
            {
                conn.Open();

                string selectUserQuery = @"SELECT * FROM thesis.joborder as jo inner join thesis.jobordermaterials as jom ON jom.jobID = jo.jobId Where jom.truck_id = '" + truck_id + "'";
                MySqlCommand cmd = new MySqlCommand(selectUserQuery, conn);

                foreach (DbDataRecord rowData in cmd.ExecuteReader())
                {
                    populateNewTableRow(rowData);
                }
            }
            catch (MySqlException ex)
            {
                System.Diagnostics.Debug.WriteLine("ERROR: " + ex.ToString());
            }
            finally
            {
                conn.Close();
            }
        }

        private void populateNewTableRow(DbDataRecord rowData)
        {
            TableRow tr = new TableRow();

            TableCell cell2 = new TableCell();
            cell2.Text = rowData.GetInt32(rowData.GetOrdinal("jobId")).ToString();
            tr.Cells.Add(cell2);

            TableCell cell3 = new TableCell();
            cell3.Text = rowData.GetString(rowData.GetOrdinal("odometerReading")).ToString();
            tr.Cells.Add(cell3);

            TableCell cell4 = new TableCell();
            cell4.Text = rowData.GetString(rowData.GetOrdinal("description")).ToString();
            tr.Cells.Add(cell4);

            TableCell cell5 = new TableCell();
            cell5.Text = rowData.GetInt32(rowData.GetOrdinal("quantity")).ToString();
            tr.Cells.Add(cell5);

            TableCell cell6 = new TableCell();
            cell6.Text = rowData.GetString(rowData.GetOrdinal("remarks")).ToString();
            tr.Cells.Add(cell6);

            TableCell cell7 = new TableCell();
            cell7.Text = rowData.GetString(rowData.GetOrdinal("mechanic")).ToString();
            tr.Cells.Add(cell7);

            tbl_MaitenanceRecord.Rows.Add(tr);// THIS (Null Reference Exception)
        }
}

我在此行收到错误System.NullReferenceException: Object reference not set to an instance of an object.

tbl_MaitenanceRecord.Rows.Add(tr);

我很确定我的代码是正确的。这个空引用异常的原因是什么？提前致谢

Answer 1

我认为更好的想法是在你的桌子上使用databind方法。检查调试器每个rowData是什么。如果上部调用中的某个对象为null，则可能会出现问题。检查你的调用堆栈并检查绑定到你的表的每个对象，因为我说它可能是一个问题。我可能也是表inicialization的问题。您可以将您的Web代码放入问题和设计师，尤其是表格部分。

ASP.net Webforms表NullException

1 个答案: