从生成的ListItem中获取下拉列表的文本

这是我的登录页面，假设密码和用户名是正确的，并使用会话获得一定的数据:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using MSSQLConnector;
using System.Data;
namespace SoftwareAnalysisAndDesign.SAD
{
    public partial class OnlineAppSyss : System.Web.UI.Page
    {
        private MSConnector connector = new MSConnector();
        string teachersubjectlistquery = null;
        private DataSet teachersubjectlistData;
        private DataTable teacheraccountdetailsTable;
        protected void Page_Load(object sender, EventArgs e)
        {
        }
        protected void Button1_Click(object sendet, EventArgs e)
        {
            Teacher();
        }
        public void Teacher()
        {
            //Connection String
            connector.ConnectionString = "Data Source=keith;Initial Catalog=SAD;Integrated Security=True";
           //Subject List                  
           teachersubjectlistquery = "select distinct CourseNo from AssessmentForm where TeacherID =" + username + "";
           teachersubjectlistData = connector.ExecuteQuery(teachersubjectlistquery);
           teachersubjectlistTable = teachersubjectlistData.Tables[0];
           Session["TeacherSubjectList"] = teachersubjectlistTable;
         }
    }

我传递数据表"teachersubjectlistTable"在另一个页面使用会话。

在我的教师页面中，我声明下拉列表来使用会话["TeacherSubjectList"]生成条目。

<asp:DropDownList runat="server" ID="SubjectList"></asp:DropDownList>

它的锚标记继续到validatessubject页:

<a class="btn btn-block" style="margin-top:-37px;margin-left:65px;" runat="server" onserverclick="TeacherSubjects_Click">Proceed</a>

及其背后的代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;
using System.Data.SqlClient;
using MSSQLConnector;
namespace SoftwareAnalysisAndDesign.SAD
{
    public partial class TeacherPage : System.Web.UI.Page
    {
        private MSConnector connector = new MSConnector();
        private DataSet SubjectlistData;
        private DataTable SubjectlistTable;
        string query = null;
        protected void Page_Load(object sender, EventArgs e)
        {
            //Populate The Select Tag with Subjects
            SubjectList.DataSource = Session["TeacherSubjectList"];
            SubjectList.DataTextField = "CourseNo";
            SubjectList.DataValueField = "CourseNo";
            SubjectList.DataBind();
        }
        protected void TeacherSubjects_Click(object sender, EventArgs e)
        {
            string getText = SubjectList.SelectedItem.Text;
            //Connection String
            connector.ConnectionString = "Data Source=keith;Initial Catalog=SAD;Integrated Security=True";
            query = "select StudentID,CourseNo,CourseDescription,Units,Day,StartTime,EndTime,Room,Instructor,Amount,Status from assessmentform where CourseNo = '" + getText + "'";
            SubjectlistData = connector.ExecuteQuery(query);
            SubjectlistTable = SubjectlistData.Tables[0];
            //Add a colum check row
            SubjectlistTable.Columns.Add("Check", Type.GetType("System.Boolean"));
            Session["ValidateSubject"] = SubjectlistTable;
            Response.Redirect("ValidateSubjectTeacher.aspx");
        }
    }
}

在我的另一个aspx页面(validatessubject)，我声明Gridview作为会话的持有者:

<asp:GridView runat="server" CssClass="table table-hover table-bordered" ID="ValidateSubject" Style="text-align: center"></asp:GridView>

及其aspx代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace SoftwareAnalysisAndDesign.SAD
{
    public partial class ValidateSubjectTeacher : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            ValidateSubject.DataSource = Session["ValidateSubject"];
            ValidateSubject.DataBind();
        }
    }
}

我不能在我的下拉列表(TeacherPage)中获得选中的项目，它只会获得第一个选中项目的数据。

在我的下拉列表(TeacherPage)中，使用查询生成了两个条目:

CmpE 515
CmpE 516

但是当我选择"CmpE 516"项并点击继续时，显示的数据只有"CmpE 515"项。如何获得其他项目/值在我的下拉列表中显示某些数据，如果用户单击某个项目?

这里的代码:

string getText = SubjectList.SelectedItem.Text;

它只会得到文本'CmpE 515'数据，即使我选择'CmpE 516'并单击继续。我如何获得下拉列表中的其他项目?

 protected void Page_Load(object sender, EventArgs e)
 {
     if(!IsPostBack)
     { 
            //Populate The Select Tag with Subjects
            SubjectList.DataSource = Session["TeacherSubjectList"];
            SubjectList.DataTextField = "CourseNo";
            SubjectList.DataValueField = "CourseNo";
            SubjectList.DataBind();
     }
  }