Why Drop down gets reset after post back? - sharepoint

Question

My requirement is to select a value from a drop down and fetch the corresponding three fields and drop down must have the selected value in it.
However my code it fetches the corresponding three fields and sets the drop down selected value to first value.
Please tel me how to solve this issue.
Below are my code at page load and corresponding methods:
public partial class RegisterWebPartUserControl : UserControl
{
string titleid;
protected void Page_Load(object sender, EventArgs e)
{
DataSet ds = new DataSet();
SPSite oSPSiteCollection = SPContext.Current.Site;
SPWeb oSPWeb = SPContext.Current.Web;
SPList oSPList = oSPWeb.Lists["Registered"];
string names = oSPWeb.CurrentUser.ToString();
TxtEmployeeName.Text = names.ToString();
SPList oSPListCalender = oSPWeb.Lists["Scheduled Courses"];
DataTable dataTable = oSPListCalender.Items.GetDataTable();
dataTable.TableName = "Table1";
ds.Tables.Add(dataTable);
ddlDrop.DataSource = ds.Tables["Table1"];
ddlDrop.DataTextField = "Title";
ddlDrop.DataValueField = "TitleID";
titleid = ddlDrop.SelectedValue;
ddlDrop.DataBind();
}
protected void ddlDrop_SelectedIndexChanged(object sender, EventArgs e)
{
FetchReadOnlyFields(titleid);
}
public void FetchReadOnlyFields(string titleID)
{
string oStartDate = null;
string oEndDate = null;
string oPrerequisite = null;
SPSite oSPSiteCollection = SPContext.Current.Site;
SPWeb oSPWeb = SPContext.Current.Web;
SPList oSPList = oSPWeb.Lists["Registered"];
SPListItemCollection oItemCollection = oSPList.Items;
SPListItem ospListItem = oItemCollection.Add();
SPList oSPList1 = oSPWeb.Lists["Scheduled Courses"];
SPListItemCollection oItemCollectionCourse = oSPList1.Items;
SPFieldCalculated titleIDCourse = (SPFieldCalculated)oItemCollectionCourse.Fields["TitleID"];
SPField fieldStartDate = oItemCollectionCourse.Fields["Start Date"];
SPField fieldEndDate = oItemCollectionCourse.Fields["End Date"];
foreach (SPListItem ospListItemCourse in oItemCollectionCourse)
{
string value = titleIDCourse.GetFieldValueAsText(ospListItemCourse["TitleID"]);
if (titleID == value)
{
oPrerequisite = ospListItemCourse["Prerequisite"].ToString();
TxtPrerequisite1.Text = SPHttpUtility.ConvertSimpleHtmlToText(oPrerequisite, oPrerequisite.Length);
oStartDate = ospListItemCourse["Start Date"].ToString();
TxtStartDate.Text = oStartDate;
oEndDate = ospListItemCourse["End Date"].ToString();
TxtEndDate.Text = oEndDate;
break;
}
}
}
}
Hope to seek your help.
Thank you

Answer 1

This code
ddlDrop.DataBind();
Should be called only once. On the first load of the page.
Try
protected void Page_Load(object sender, EventArgs e)
{
if(!Page.IsPostBack){ // this is what has changed
DataSet ds = new DataSet();
SPSite oSPSiteCollection = SPContext.Current.Site;
SPWeb oSPWeb = SPContext.Current.Web;
SPList oSPList = oSPWeb.Lists["Registered"];
string names = oSPWeb.CurrentUser.ToString();
TxtEmployeeName.Text = names.ToString();
SPList oSPListCalender = oSPWeb.Lists["Scheduled Courses"];
DataTable dataTable = oSPListCalender.Items.GetDataTable();
dataTable.TableName = "Table1";
ds.Tables.Add(dataTable);
ddlDrop.DataSource = ds.Tables["Table1"];
ddlDrop.DataTextField = "Title";
ddlDrop.DataValueField = "TitleID";
ddlDrop.DataBind();
}
titleid = ddlDrop.SelectedValue;
}