我如何从 PHP 页面获取城市 ID

我正在为我的网站创建一个注册表。在我的注册表中，有两个选择框来选择用户的地区和城市。所以我需要这样做，当用户选择他们的地区时，然后自动显示城市选择框，其中包含与上述所选地区相关的城市。为此，我使用了AJAX和PHP。我使用 findcity.php 页面在我的注册.php页面中显示城市。我的问题是当我尝试从注册.php页面获取城市 ID 时，我无法获得它。我需要将其他数据从注册.php页面发送到数据库。

从我的注册.php页面

<div>
<label for="district">District <img src="../images/required_star.png" alt="required" /> : </label>
<?php
    require_once ('../includes/config.inc.php');    
    require_once( MYSQL2 );
    $query="select * from district order by district_id";
    $result = mysqli_query( $dbc, $query);
        echo '<select name="district" class="text" onChange="getCity(' . "'" . 'findcity.php?district=' . "'" . '+this.value)">';
        echo '<option value="">-- Select District --</option>';
        while( $row = mysqli_fetch_array($result, MYSQLI_NUM)) { 
            echo '<option value="' . $row[0] . '"';
            // Check for stickyness: 
            if ( isset( $_POST['district']) && ( $_POST['district'] == $row[0] ))    
                echo ' selected="selected"';
                echo " >$row[1]</option>";    
        }
        echo '</select>';
?> 
</div>    
<div>
    <label for="city">City <img src="../images/required_star.png" alt="required" /> : </label>
    <input type="hidden" name="reg_locationid" id="reg_locationid" value="56" />
    <div id="citydiv" style="position: relative; top: -14px; left: 130px; margin-bottom: -26px;">
        <select name="city" class="text">
            <option>-- Select City --</option>
        </select>
    </div>
</div>

这是 FindCity.php 页面

<?php
$districtId=$_GET['district'];
require_once ('../includes/configaration.inc.php'); 
require_once( MYSQLCONNECTION );
$query="select city_id, city_name from city2 where district_id=$districtId";
$result=mysqli_query( $dbc, $query);

echo '<select name="city" class="text">
        <option>-- Select City --</option>';
while($row=mysqli_fetch_array($result, MYSQLI_NUM)) { 
    echo '<option value="' . $row[0] . '"';
    // Check for stickyness: 
    if ( isset( $_POST['city']) && ( $_POST['city'] == $row[0] )) { 
        echo ' selected="selected"';
        //echo '<input type="hidden" name="city"  value="' . $row[0] . '"'; 
    }
        echo " >$row[1]</option>";  
}
echo '</select>';

？>

这是我的 Ajax 函数

function getXMLHTTP() { //function to return the xml http object
    var xmlhttp=false;  
    try{
        xmlhttp=new XMLHttpRequest();
    }
    catch(e)    {       
        try{            
            xmlhttp= new ActiveXObject("Microsoft.XMLHTTP");
        }
        catch(e){
            try{
            xmlhttp = new ActiveXObject("Msxml2.XMLHTTP");
            }
            catch(e1){
                xmlhttp=false;
            }
        }
    }
    return xmlhttp;
}

function getCity(strURL) {      
    var req = getXMLHTTP();
    if (req) {
        req.onreadystatechange = function() {
            if (req.readyState == 4) {
                // only if "OK"
                if (req.status == 200) {                        
                    document.getElementById('citydiv').innerHTML=req.responseText;                      
                } else {
                    alert("There was a problem while using XMLHTTP:'n" + req.statusText);
                }
            }               
        }           
        req.open("GET", strURL, true);
        req.send(null);
    }
}