Question

I have asp.net page dropdownlist and button when choose my group from dropdownlist
and click button then button send selected value (group-id) via query string
then page view group detail based on id in query string this happens the first time
but when I change group from dropdownlist the query string still has the last id
and my code

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

    if (Request.QueryString["id"] != null)
    {
        FillData();
        div_General.Visible = true;
        div_Special.Visible = true;
        dropdownlist1 .SelectedValue = Request.QueryString["id"];
    }
}

protected void button1_Click(object sender, EventArgs e)
{
    if (dropdownlist1 .SelectedIndex == 0)
    {
        par_ErrorMessage.InnerText = "choose group first  ...";
        par_ErrorMessage.Visible = true;
    }
    else Response.Redirect("Authority.aspx?id=" + dropdownlist1.SelectedValue);
}

I figured the problem in this when I click button and suppose that new value in
dropdownlist page life cycle go to page load first and in this code

  dropdownlist1 .SelectedValue = Request.QueryString["id"];

Return selected value to the last one before read it from button1_click

my FillList Method

     private void FillList()
{
    oGroup = new Cls_Groups();
    cmb_Group.DataSource = oGroup.LoadGroups();
    cmb_Group.DataBind();

    cmb_Group.Items.Insert(0, "-- اختر مما يلي --");
}

Please, I need help

Answer 1

You can Select Value for Drop Down after Page Load Event

protected void Page_Load(object sender, EventArgs e)
{
   if (!IsPostBack) 
      {
        FillList();
        Viewstate["id"] = Request.QueryString["id"];
         if (Request.QueryString["id"] != null)
           {
            FillData();
            div_General.Visible = true;
            div_Special.Visible = true;

           }
      }
}

Now in Page_PreRender you can Select Value in dropdown like this:-

protected void Page_PreRender(object sender, EventArgs e)
{
  if(!Page.IsPostBack)
 {
   if (ViewState["id"] != null)
      {
          dropdownlist1 .SelectedValue = ViewState["id"].ToString();
       }
  }
}

Hope this will help you