为什么用户单击Load按钮会出错？

嗨，我有一个脚本，当用户单击Load More按钮时，Ajax将请求新的内容并显示给用户，但是如果所有的内容都已加载，那么用户再单击Load按钮，则会导致错误并反复显示多个Load按钮。下面是我的代码，需要知道如何解决这个问题。如果没有内容可加载，则需要禁用按钮。谢谢各位！！

ajax_more.php：

 <?php
include("config.php");


if(isSet($_POST['lastmsg']))
{
$lastmsg=$_POST['lastmsg'];
$result=mysql_query("select * from messages where mes_id<'$lastmsg' limit 3");
$count=mysql_num_rows($result);
while($row=mysql_fetch_array($result))
{
$msg_id=$row['mes_id'];
$message=$row['msg'];
?>


<li>
<?php echo $message; ?>
</li>


<?php
}


?>

<div id="more<?php echo $msg_id; ?>" class="morebox">
<a href="#" id="<?php echo $msg_id; ?>" class="more">more</a>
</div>

<?php
}
?>

loadmore.php

<?php
include('config.php');

?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Twitter Style load more results.</title>
<link href="frame.css" rel="stylesheet" type="text/css">
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/
libs/jquery/1.3.0/jquery.min.js"></script>

<script type="text/javascript">
$(function() {
//More Button
$('.more').live("click",function() 
{
var ID = $(this).attr("id");
if(ID)
{
$("#more"+ID).html('<img src="moreajax.gif" />');

$.ajax({
type: "POST",
url: "ajax_more.php",
data: "lastmsg="+ ID, 
cache: false,
success: function(html){
$("ol#updates").append(html);
$("#more"+ID).remove();
}
});
}
else
{
$(".morebox").html('The End');

}


return false;


});
});

</script>
<style>
body
{
font-family:Arial, 'Helvetica', sans-serif;
color:#000;
font-size:15px;

}
a { text-decoration:none; color:#0066CC}
a:hover { text-decoration:underline; color:#0066cc }
*
{ margin:0px; padding:0px }
ol.timeline
    { list-style:none}ol.timeline li{ position:relative;border-bottom:1px #dedede dashed; padding:8px; }ol.timeline li:first-child{}
    .morebox
    {
    font-weight:bold;
    color:#333333;
    text-align:center;
    border:solid 1px #333333;
    padding:8px;
    margin-top:8px;
    margin-bottom:8px;
    -moz-border-radius: 6px;-webkit-border-radius: 6px;
    }
    .morebox a{ color:#333333; text-decoration:none}
    .morebox a:hover{ color:#333333; text-decoration:none}
    #container{margin-left:60px; width:580px }

</style>
</head>

<body>
<div style="padding:4px; margin-bottom:10px; border-bottom:solid 1px #333333; "><h3>Tutorial Link <a href="http://9lessons.blogspot.com/2009/12/twitter-style-load-more-results-with.html">Click Here</a></h3></div>
<div id='container'>
<ol class="timeline" id="updates">
<?php
$sql=mysql_query("select * from messages  LIMIT 3");
while($row=mysql_fetch_array($sql))
{
$msg_id=$row['mes_id'];
$message=$row['msg'];
?>
<li>
<?php echo $message; ?>
</li>
<?php } ?>
</ol>
<div id="more<?php echo $msg_id; ?>" class="morebox">
<a href="#" class="more" id="<?php echo $msg_id; ?>">more</a>
</div>
</div>

</body>
</html>

<?php
include("config.php");

$count=0;
$done=false;
if(isSet($_POST['lastmsg']))
{
$lastmsg=$_POST['lastmsg'];
$result=mysql_query("select * from messages where mes_id<'$lastmsg' limit 3");
$check=mysql_result(mysql_query("select mes_id from messages ORDER BY mes_id ASC limit 1"));
$count=mysql_num_rows($result);
while($row=mysql_fetch_array($result))
{
$msg_id=$row['mes_id'];
$message=$row['msg'];
if($row['mes_id']==$check){$done=true;}
$count++;
?>


<li>
<?php echo $message; ?>
</li>


<?php
}

if($count>0 && !$done){
?>

<div id="more<?php echo $msg_id; ?>" class="morebox">
<a href="#" id="<?php echo $msg_id; ?>" class="more">more</a>
</div>

<?php
}
}
?>

Explanation: You were unconditionally outputting the more link. With the changes made, the script checks if more than 0 messages have been loaded from the table before outputting a more link. I have also updated it to check if the current batch is the last and not output the more div if it is.

In the php section, only display the More button if your returned row size count is greater than 0

Edge cases:

If your database table size increases by n rows, you will repeat n records each time you hit More
As above, but if records are removed, you will miss out records

Security issues:

SQL injection by sending "0'; truncate messages;--" in the last message post field
Cross site scripting - if users can submit messages with HTML/JavaScript they will be returned in the content without escaping.

In both cases above, use. MySQL escape string ( http://php.net/manual/en/function.mysql-real-escape-string.php ), or use mysqli, and use htmlentities ( http://php.net/manual/en/function.htmlentities.php )

try this code;

   $.ajax({
**$("#load_buton").attr("disabled","disabled");**
    type: "POST",
    url: "ajax_more.php",
    data: "lastmsg="+ ID, 
    cache: false,
    success: function(html){
    $("ol#updates").append(html);
    $("#more"+ID).remove();
**$("#load_buton").removeAttr("disabled");**
    });