Dropdownlist is Empty after Postback

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ASP.NET

Hi Friends,

I am loading data into dropdownlist from sql as shown below:

if (!IsPostBack)
 
            {
 
               string connStr = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
 da =new SqlDataAdapter("sp_LabelNames", connStr);
 
               DataSet ds = new DataSet();
 
                da.Fill(ds);
 
                lblAdmitto.Text = ds.Tables[0].Rows[0][1].ToString();
 
                lblVitalSigns.Text = ds.Tables[0].Rows[1][1].ToString();
 
                lblActivity.Text = ds.Tables[0].Rows[2][1].ToString();
 
                lblDiet.Text = ds.Tables[0].Rows[3][1].ToString();
 
                lblFluids.Text = ds.Tables[0].Rows[4][1].ToString();
 
                lblNursingOrders.Text = ds.Tables[0].Rows[5][1].ToString();
 
                lblMedications.Text = ds.Tables[0].Rows[6][1].ToString();
 
                lblBetaBlockers.Text = ds.Tables[0].Rows[7][1].ToString();
 
                lblAnalgesics.Text = ds.Tables[0].Rows[8][1].ToString();
 
                   
 

 da=new SqlDataAdapter("sp_SelectAdminto",connStr);
 ds =new DataSet();
 da.Fill(ds);
 ddlGeneral.DataSource = ds.Tables[0];
 ddlGeneral.DataTextField ="Text";
 ddlGeneral.DataBind();
 ListItem item = new ListItem("--Select--", "0");
 ddlGeneral.Items.Insert(0, item);

but when I do postback,by performing some operations,drop downlist is empty.

I googled and found we need to make sure that EnableViewState="True" in page directory and also in each controls of page (ie) enabled View State=true. but still issue exists:

steps:

1)pageload> data exists {as it is not postback)

2)selected index> postback,but data exists and going to some say pageB and again coming to pageA

3)again selected index>postback,but data is empty in drop down.

this is the issue.

Drop downlist selected index changed event:
protected void ddlVitalSigns_SelectedIndexChanged(object sender, EventArgs e)

  {
 
       if (ddlVitalSigns.SelectedIndex < 0)
 
        {
 
            lblItemcommentsmsg.Text ="";
 
        }
 
       else
 
        {
 
            lblItemcommentsmsg.Text = ddlVitalSigns.SelectedItem.Value.ToString();
 
           foreach (ListItem li in ddlVitalSigns.Items)
 
            {
 
               if (li.Selected == true)
 
                    li.Attributes.Add("style", "background:red;");
 
 }
 
           
 
DropDownList ddlClicked = sender as DropDownList;
 
           foreach (Control control in pnlMain.Controls)
 
            {
 
               
 
if (control is DropDownList)
 
                {
 
                   
 
DropDownList ddl = control as DropDownList;
 
                   
 
if (ddl.ID != ddlClicked.ID)
 
                    {
 
                        ddl.SelectedIndex = 0;
 
                    }
 
                }
 
            }
 

            Session["X"] = lblItemcommentsmsg.Text;
 
        }
 
    }

Below is .aspx page ddl control code:

<td class="style25">

     <asp:Label ID="lblVitalSigns" runat="server" Text="Label"></asp:Label>

  </td>

  <td class="style26">

     <asp:DropDownList ID="ddlVitalSigns" runat="server" Height="16px"

   style="margin-left: 0px" Width="356px" AutoPostBack="True"

       onselectedindexchanged="ddlVitalSigns_SelectedIndexChanged">

      </asp:DropDownList>

  </td>

Please help me ASAP.