从生成的 ListItem 中获取 DropdownList 的文本

Question

这是我的登录页面，假设密码和用户名正确并使用会话获取一定的数据：

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;
         }
    }

我使用 Session 在另一个页面中传递 DataTable“teachersubjectlistTable”。

在我的教师页面中，我声明下拉列表以使用 Session["TeacherSubjectList"] 生成项目。

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

它的锚标签进入ValidateSubject页面：

<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 (ValidateSubject) 中，我将 Gridview 声明为会话的持有者：

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

及其背后的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();
        }
    }
}

我无法在我的下拉列表（TeacherPage）中获取所选项目，它只会获取所选第一个项目的数据。

在我的下拉列表（TeacherPage）中，使用查询生成了两个项目：

CmpE 515
CmpE 516

但是当我选择“CmpE 516”项目并单击继续时，显示的数据只是“CmpE 515”项目。如果用户单击某个项目，如何让我的下拉列表中的其他项目/值显示某些数据？

这里的代码：

string getText = SubjectList.SelectedItem.Text;

即使我选择“CmpE 516”并单击“继续”，它也只会获取文本“CmpE 515”数据。如何获取下拉列表中的其他项目？

Answer 1

您不应该在每次页面加载时绑定下拉列表，使用IsPostBack 属性检查页面是否第一次加载，只有在这种情况下才能像这样绑定您的下拉列表：-

 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();
     }
  }

同样适用于您的ValidateSubjectTeacher 页面。