Postback Asp.Net Webforms

Question

I just started working with WebForms and it became a question, due to always messing with the asp.net mvc.

Supposing I have one DropDownList and populated the DataSource of it with various records, when held the PostBack i can’t recover the data that is in that DropDownList, have any way to recover these data? what is the best way to work with the data in PostBack . Thank you.

    private void PopularEmpresasDoGrupoDoUsuario()
    {
        VOB2BUser voUser = GetSessionUser();
        DAOB2BCompany daoCompany = new DAOB2BCompany(((Page)Page).DATABASE);
        DAOB2BUser daoUser = new DAOB2BUser(((Page)Page).DATABASE);
        DAOB2BCompanyGroupUser daoCompanyGroupUser = new DAOB2BCompanyGroupUser(((Page)Page).DATABASE);

        var userGroup = daoCompanyGroupUser.GetUserGroup(voUser.IdUser);
        if (userGroup == null)
        {
            divEmpresasDoGrupoDoUsuario.Visible = false;
        }
        else
        {
            divEmpresasDoGrupoDoUsuario.Visible = true;

            dropDownListEmpresasDoGrupoDoUsuario.DataSource = daoCompany.GetEmpresasVinculadasNoGrupoDeEmpresa(userGroup.IdGroup);
            dropDownListEmpresasDoGrupoDoUsuario.DataBind();

            upEmpresasDoGrupoDoUsuario.Update();

            dropDownListEmpresasDoGrupoDoUsuario.SelectedIndex = 0;
            dropDownListEmpresasDoGrupoDoUsuario_SelectedIndexChanged(dropDownListEmpresasDoGrupoDoUsuario, new EventArgs());
        }
    }

    protected void Page_Load(object sender, EventArgs e)
    {

        if (!this.Page.IsPostBack)
        {                
            if (Session["USER"] != null)
            {                    
                PopularEmpresasDoGrupoDoUsuario();
                SetUserPermissions(fc);
            }
        }            
    }

Answer 1

You can, in every Load event of the page, check whether it is a postback or not. And then take the data that is in the dropdown source. Example:

I used a Datatable as an example

protected void Page_Load(object sender, EventArgs e)
{

    if (!this.IsPostBack)
    {
          //Não é postback
    }
    else
    {
         DataTable dt  = dropDownList1.DataSource as DataTable;
         if (dt != null)
         {
            //Faz o que precisa com o DataTable
         } 
    }
}

ps. Be careful, as the code will run on any postback that happens, it can considerably affect the performance.