how to display selected dropdown value when user edit any form?

问题

I have created dependent drop down of state and city. It is property submission form. When user edit the form, I want to display selected state and city. I managed to display selected state somehow. I have written get_city function function.php and call it through ajax.I have two different tables i.e. state and city. So problem is I dont understand how to show selected city?? This is my code for drop down

<select name="state" id="state" class="select-submit2">
   <option value="">Select state</option>

   <?php 
   $property_id = $_GET['listing_edit']; 
   $property_state = get_post_meta($property_id, state, true);
   $result=$wpdb->get_results("select * from states");
   //$wpdb->get_results($query);
   foreach($result as $row) {
      $state_id=$row->state_id;
      $state_name=$row->state_name;     
?>
<option value="<?php echo $state_id; ?>" <?php if($property_state == $state_id){ echo 
 'selected="selected"';} ?>><?php echo $state_name; ?></option>
<?php 
      //echo '<option value='.$state_id.'>'.$state_name.'</option>';
   }
?>          
</select>
<input type="hidden" name="edit_id" id="edit_id" value="<?php echo $edit_id;?>">
<select name="district" id="district" required class="select-submit2">
   <option value="">Select District</option>
</select> 

In the above code i am displaying selected state. I searched on google and found that I have to pass post id to function in function.php. This is my code for get_city function in function.php file

function getcity() {

global $wpdb;

   if($_POST['state']) {
      $id = $_POST['state'];
      global $edit_id;
      $property_id = $edit_id; 
      $district = get_post_meta($property_id, 'district', true);
      $result=$wpdb->get_results("SELECT * FROM districts WHERE state_id='$id'");

      foreach($result as $row) {
         $city_name = $row->district_name;
         $city_id = $row->district_id;
?>
<option value="<?php echo $city_id; ?>" <?php if($district == $city_id){ echo 'selected="selected"';} ?>><?php echo $city_name; ?></option>
<?php    
         //echo '<option value="'.$city_id.'">'.$city_name.'</option>';                 
      }
   }
}
add_action("wp_ajax_nopriv_getcity", "getcity");
add_action("wp_ajax_getcity", "getcity");

This is my js code...

 jQuery(document).ready(function($) {

  $('#state').on('change', function() {

   var state  = $('#state').val();
   var edit_id = $('#edit_id').val();

   $.ajax
   ({
    type : "POST",
    url  : "http://whitecode.in/demo/plotsup_plot/wp-admin/admin-ajax.php",
    data :{'action' : 'getcity', 'state' : state , 'edit_id' : edit_id },
    success: function(html) {

      $("#district").removeAttr("disabled");
      $("#district").html(html);
     }

    });
   });

 <input type="hidden" name="edit_id" id="edit_id" value="<?php echo $edit_id;?>">

回答1:

You must put the above code in a function. Let the function name be myFunction(). If you want to pass the post id to the function, call the function with post id as its argument, ie, myFunction($postid) where $postid is the post id. Please do not forget to call function from the post loop so that function will call for every postid.

回答2:

I personally load a for each state, with style="display:none;", afterwards, when user selects state the appropriate changes style="display:none;" to style="display:inline;"

回答3:

Try this and let me know if it works or not. The change is made on two lines global $edit_id; has been removed and the $property_id line has been changes. Please apply the changes properly and let me know if they are ok.

<?php
function getcity() {

global $wpdb;

if($_POST['state']) {
  $id = $_POST['state'];
  $property_id = $_POST['edit_id']; 
  $district = get_post_meta($property_id, 'district', true);
  $result=$wpdb->get_results("SELECT * FROM districts WHERE state_id='$id'");

  foreach($result as $row) {
     $city_name = $row->district_name;
     $city_id = $row->district_id;
 ?>
<option value="<?php echo $city_id; ?>" <?php if($district == $city_id){ echo 'selected="selected"';} ?>><?php echo $city_name; ?></option>
<?php    
     //echo '<option value="'.$city_id.'">'.$city_name.'</option>';                 
  }
}
}
add_action("wp_ajax_nopriv_getcity", "getcity");
add_action("wp_ajax_getcity", "getcity");

来源：https://stackoverflow.com/questions/25800727/how-to-display-selected-dropdown-value-when-user-edit-any-form