How to create SelectIndexChanged event for multiple selection in asp.net

Question

I want to select multiple item from checkbox list and then fill another check Box list on select index changed event of First check box list but after one selection its not working for another selected items because of "Auto Post Back = true" while debbuging i can see pointer start from page load event. I want after selection of all Item it should be fire "ddlregion_SelectedIndexChanged" so that I can able see all selected Item related value in another check Box List.

protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindRegion();
            }
        }

Due to this its not fetching data for another selected Items how to solve this issues Please help me.

ddlRegion Code Binding:

public void BindRegion()
        {
            OracleCommand Cmd = new OracleCommand("select * from regions", con);
            Cmd.CommandType = CommandType.Text;
            OracleDataAdapter da = new OracleDataAdapter();
            DataSet ds = new DataSet();
            da.SelectCommand = Cmd;
            da.Fill(ds);
            ddlregion.DataSource = ds;
            ddlregion.DataTextField = "REGION_DESC";
            ddlregion.DataValueField = "REGION_CODE";
            ddlregion.DataBind();

        }

Select Index Changed Event

 protected void ddlregion_SelectedIndexChanged(object sender, EventArgs e)
 {
  ddlDepot.Items.Clear();
  ddlDepot.Items.Add(new ListItem("--Select Depot--", ""));
  foreach (ListItem item in ddlregion.Items)
   {

   if (item.Selected == true)
   {
string str = "select d.depot_code, d.depot_description from regions r, sub_regions sr, depots d where r.region_code = sr.region_code and sr.sub_region_code = d.sub_region_code and active = 'Y' and r.region_code in " + ddlregion.SelectedValue + "";
                    OracleCommand Cmd = new OracleCommand(str, con);
                    Cmd.CommandType = CommandType.Text;
                    OracleDataAdapter da = new OracleDataAdapter();
                    DataSet ds = new DataSet();
                    da.SelectCommand = Cmd;
                    da.Fill(ds);
                    ddlDepot.DataSource = ds;
                    ddlDepot.DataTextField = "DEPOT_DESCRIPTION";
                    ddlDepot.DataValueField = "DEPOT_CODE";
                    ddlDepot.DataBind();
                }
            }
        }

Answer 1

You need to build your region list for the SQL, then once done call your SQL and Bind.

 string regions = "";
 bool regionSelected = false;
  foreach (ListItem item in ddlregion.Items)
  {  
   if (item.Selected == true)
    {
        regions += item.SelectedValue + ",";
        regionSelected = true;
    }
 
  } 
     // looping done so clean up string for SQL
     regions = "(" + regions.TrimEnd(',') + " )";

 //only run if a region is selected
 if(regionSelected)
 {
 string str = "select d.depot_code, d.depot_description from regions r, sub_regions sr, 
 depots d where r.region_code = sr.region_code and      
 sr.sub_region_code = d.sub_region_code and active = 'Y' and  r.region_code    
 in " + regions;
                OracleCommand Cmd = new OracleCommand(str, con);
                Cmd.CommandType = CommandType.Text;
                OracleDataAdapter da = new OracleDataAdapter();
                DataSet ds = new DataSet();
                da.SelectCommand = Cmd;
                da.Fill(ds);
                ddlDepot.DataSource = ds;
                ddlDepot.DataTextField = "DEPOT_DESCRIPTION";
                ddlDepot.DataValueField = "DEPOT_CODE";
                ddlDepot.DataBind();
 }