Selectbox

  <!-- select2 -->
  <link href="css/select/select2.min.css" rel="stylesheet">


  <script src="js/jquery.min.js"></script>



<?php

    $AAnagrafica_id[1] = "op1";
    $AAnagrafica_nominativo[1] = "opzione1";
    $AAnagrafica_id[2] = "op2";
    $AAnagrafica_nominativo[2] = "opzione2";
    $AAnagrafica_id[3] = "op3";
    $AAnagrafica_nominativo[3] = "opzione3";
    $AAnagrafica_id[4] = "op4";
    $AAnagrafica_nominativo[4] = "opzione4";
    ?>










                          <SELECT class="select2_single " tabindex="-1" size=1 name='listbox_id'  id='listbox_id'  >
                              <OPTION>Selezionare </OPTION>
<?php
                                            $Ind2 = 1;
                                            while ( $Ind2 <= 999) {
                                                 if ( $AAnagrafica_id[ $Ind2 ]  == '' ) { $Ind2 = 999;  }
                                                 else
                                                 {
                                                    echo ("<OPTION value=" .  $AAnagrafica_id[ $Ind2 ] . "          >" . $AAnagrafica_nominativo[ $Ind2 ] . "</OPTION>" );

                                                 }
                                            $Ind2++;
                                            }
                                   ?>
                                            </SELECT>










                <script>
               function onChange_leggi_info() {


                   $.post(
		'programma_post.php',
		{ 	},
		function( data ){


      $('#listbox_id').val('op2');

            } /* fine function */
	);  /*  fine POST */

 } //chiudo function principale

//lancio della function



    onChange_leggi_info();






                </script>





  <script src="js/bootstrap.min.js"></script>

  <!-- bootstrap progress js -->
  <script src="js/progressbar/bootstrap-progressbar.min.js"></script>
  <script src="js/nicescroll/jquery.nicescroll.min.js"></script>
  <!-- icheck -->
  <script src="js/icheck/icheck.min.js"></script>
  <!-- tags -->
  <script src="js/tags/jquery.tagsinput.min.js"></script>
  <!-- switchery -->
  <script src="js/switchery/switchery.min.js"></script>
  <!-- daterangepicker -->
  <script type="text/javascript" src="js/moment/moment.min.js"></script>
  <script type="text/javascript" src="js/datepicker/daterangepicker.js"></script>

  <!-- select2 -->
  <script src="js/select/select2.full.js"></script>

  <!-- Autocomplete -->
  <script type="text/javascript" src="js/autocomplete/countries.js"></script>
  <script src="js/autocomplete/jquery.autocomplete.js"></script>
  <!-- pace -->
  <script src="js/pace/pace.min.js"></script>

  <script src="js/custom.js"></script>


  <!-- select2 -->
  <script>
    $(document).ready(function() {
      $(".select2_single").select2({

      });

    });
  </script>
  <!-- /select2 -->