Change in drop-down updates textbox in same dynamically created row

You were so very helpful this morning, that I thought it would be a good bet I could get help on this. I have dynamically created rows in a table, one field is a drop-down to select a fee type. When this is changed I want to update a field in the same row with the $$ amount. I'm getting the correct fee and the correct id from my alerts ("the fee is class_fee[37] and the amount is 225.00"), but the textbox with the fee $$ is not updating. The the textbox id is id="class_fee[<?php echo $i ?>]" Here is the jQuery (maybe I'm all wrong in how I'm identifying that $$ box?):

    $(".fee_id_select").bind("change",function ()
{  
        var $class_fee = 'class_fee[' + this.id + ']';

      jQuery.getJSON(
          'get_fee_json.php',
          {'id': this.value},
          update_fee_amount
      );
        function update_fee_amount(data, textStatus)
        {
            var fee = data || {}; 
      alert('the fee is ' + $class_fee + ' and the amount is ' + fee.fee_amount);                   
            jQuery('#' + $class_fee).val(fee.fee_amount || '');    
        }                                   
});

Here is the actual HTML inside a foreach loop:

            <td>
                <input type="text" 
                name="stude开发者_如何学Gonts[<?php echo $i ?>][class_fee]" 
                id="class_fee[<?php echo $i ?>]"
                value="<?= html($class['class_fee']) ?>" 
                size="6" >
            </td>  

(yes, there are brackets. $i is the unique id number from a class registration table.)

Here is a jSon response:

{"fee_amount":"25.00"}

These all look like great answers, and I've tried them all, but the textbox for the fee amount is not changing. I don't have any errors in Firebug. I'm puzzled.

Because the element is injected into the DOM tree after document load you can't use .bind(). You should use .live() or better than that .delegate()

   $(".fee_id_select").live("change",function ()
{  
        var $class_fee = 'class_fee[' + this.id + ']';

      jQuery.getJSON(
          'get_fee_json.php',
          {'id': this.value},
          update_fee_amount
      );
        function update_fee_amount(data, textStatus)
        {
            var fee = data || {}; 
      alert('the fee is ' + $class_fee + ' and the amount is ' + fee.fee_amount);                   
            jQuery('#' + $class_fee).val(fee.fee_amount || '');    
        }                                   
});

http://api.jquery.com/live/

http://api.jquery.com/delegate/

At the moment, $class_fee contains class_fee[37], whereas the id you want (probably) is class_fee37.

Something like this should work, I think

jQuery('#class_fee' + this.id).val(fee.fee_amount || '');

If it doesn't, please post the HTML for the textbox.