CODEWITHSUNDEEP
c#asp.net
ShoeLace1291
ShoeLace1291

Reputation: 4698

asp value of dropdownlist selection resets to 0 after onchange

I have a page with a dropdownlist where you select a semester. Each has it's own unique id. When a semester is selected, I want to populate a dropdownlist of courses from a stored procedure(sp). This sp uses a parameter called semesterID, so it gets all courses with the selected semesterID. My problem is that the semester list always returns 0. Why does this happen?

Here is my C# code:

 private void PopulateSemesterList()
        {
            string connstring;
            connstring = ConfigurationManager.ConnectionStrings["dbConn"].ConnectionString;
            SqlConnection conn = new SqlConnection(connstring);

            SqlCommand cmd = new SqlCommand("dbo.GetSemesters", conn);
            conn.Open();

            DDSemesters.DataSource = cmd.ExecuteReader();
            DDSemesters.DataTextField = "semesterName";
            DDSemesters.DataValueField = "semesterId";
            this.DataBind();

            conn.Close();
            conn.Dispose();

            DDSemesters.Items.Insert(0, new ListItem("Select Semester", "0"));
            DDSemesters.SelectedIndex = 0;
        }

        protected void DDSemesters_SelectedIndexChanged(object sender, EventArgs e)
        {
            string connstring;
            connstring = ConfigurationManager.ConnectionStrings["dbConn"].ConnectionString;
            SqlConnection conn = new SqlConnection(connstring);

            SqlCommand cmd = new SqlCommand("dbo.GetCourses", conn);
            cmd.Parameters.Add(new SqlParameter("@semesterId", DDSemesters.SelectedItem.Value));
            selectedCourseLbl.Text = DDSemesters.SelectedItem.Value;

            conn.Open();

            DDCourses.DataSource = cmd.ExecuteReader();
            DDCourses.DataTextField = "courseName";
            DDCourses.DataValueField = "courseId";
            this.DataBind();

            conn.Close();
            conn.Dispose();

            DDCourses.Items.Insert(0, new ListItem("Select Course", "0"));
            DDCourses.SelectedIndex = 0;
            DDCourses.Visible = true;
            CoursesLbl.Visible = true;
        }

Here is my ASP:

<asp:Label ID="Label1" runat="server" Text="Select Semester"></asp:Label><br />
        <asp:DropDownList ID="DDSemesters" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DDSemesters_SelectedIndexChanged" DataTextField="semesterName" DataValueField="semesterId"></asp:DropDownList><br />
        <asp:Label ID="selectedCourseLbl" runat="server" Text="Label"></asp:Label>
        <asp:Label ID="CoursesLbl" runat="server" Text="Select Course" Visible="false"></asp:Label><br />
        <asp:DropDownList visible="false" ID="DDCourses" runat="server" AutoPostBack="True" OnSelectedIndexChanged="DDCourses_SelectedIndexChanged" DataTextField="courseName" DataValueField="courseId"></asp:DropDownList><br />

Upvotes: 0

Views: 100

Answers (2)

Anto
Anto

Reputation: 50

Use Datatable to fetch the values in drop down list. 

 string connstring;
            connstring = ConfigurationManager.ConnectionStrings["dbConn"].ConnectionString;
            SqlConnection conn = new SqlConnection(connstring);
            SqlCommand cmd = new SqlCommand("dbo.GetSemesters", conn);
            conn.Open();
           DataTable dt  = new DataTable();
           dt = cmd.ExecuteReader();
           if (dt.Rows.Count > 0)
           {
            DDSemesters.DataSource = dt;
            DDSemesters.DataTextField = "semesterName";
            DDSemesters.DataValueField = "semesterId";
            DDSemesters.DataBind();
            }
            conn.Close();
            conn.Dispose();
            DDSemesters.Items.Insert(0, "Select Semester");

Upvotes: 0

Tim Schmelter
Tim Schmelter

Reputation: 460168

I'd bet any money that your Page_Load looks like this:

protected void Page_Load(Object sender, EventArgs e)
{
    PopulateSemesterList();
    // maybe other code
}

change it to

protected void Page_Load(Object sender, EventArgs e)
{
    if(!IsPostBack)
        PopulateSemesterList();
    // maybe other code
}

The problem is that PopulateSemesterList clears the selection, so you should do this only on the initial load and not on every postback. Page_Load happens before all events like the SelectedIndexChanged-event of the DropDownList.

Upvotes: 4

Related Questions