使用下拉列表进行链式选择

Question

在下面的这段代码中，我将数据库中的主题列表打印到下拉列表中。选择主题后，下一个名为 section 的下拉菜单应通过在数据库中查找主题名称来显示每个主题的部分。

这是我能够做的，但它不起作用，任何帮助的人，请忽略我的编码风格，因为我是初学者。提前谢谢你。

主要代码：

    <div>
      Subject:
  <?php
        $conn = new mysqli('fgdfgfg', 'fggfdgfr', 'fgfgf', 'fgfgfgf') or die('Cannot connect to db');
        $result = $conn->query("select name from class");
        echo "<select name='subject' nChange='getSection('findsection.php?subject='+this.value)'>";
        while ($row = $result->fetch_assoc()) {
            unset($id, $name);
            $name = $row['name'];
            echo '<option value="subject">' . $name . '</option>';
        }
        echo "</select>";
        ?> 
    </div>
    <br>  
    <div id="sectiondiv">
        Section: 
        <select name="select">
        </select>
    </div>

findsection.php

<? $subject=intval($_GET[‘subject’]);;
$servername = "localhost";
$username = "fhdfhdfhf";
$password = "ghhfghgh";
$dbname = "ghghgh";
$mysqli  = new Mysqli($servername, $username, $password, $dbname) or mysqli_error($mysqli);
$section = $mysqli->query("SELECT section FROM class WHERE name = '$subject'")->fetch_object()->section; 
$result=mysql_query($section);?>
<select name="section">
<? while ($row = $result->fetch_assoc()) { ?>
   <option value><?=$row['section']?></option>
<? } ?>
</select>

JS代码：

<script type="text/javascript">
function getSection(strURL)
{         
 var req = getXMLHTTP(); // fuction to get xmlhttp object
 if (req)
 {
  req.onreadystatechange = function()
 {
  if (req.readyState == 4) { //data is retrieved from server
   if (req.status == 200) { // which reprents ok status                    
     document.getElementById('sectiondiv').innerHTML=req.responseText;
  }
  else
  { 
     alert("There was a problem while using XMLHTTP:\n");
  }
  }            
  }        
req.open("GET", strURL, true); //open url using get method
req.send(null);
 }
}
</script>

Answer 1

问题似乎出在这条线上

<select name='subject' onchange='getSection('findsection.php?subject='+this.value)'>

this.value 没有按照您的意愿传递。这里this 的值是window 对象而不是select 标签对象。

所以我建议你在getSection函数本身中获取当前值的值，并在函数内部形成url，然后进行http请求。