无法在php脚本中从android获取post数据

我正在尝试从android到php 获取一些用户字段

$mobile_num被正确填充，但其他变量（如$user_name、$latitude、$longitude）仍然为空。

<?php
include('ConnectDB.php');
$user_name=$_POST['userName'];
$mobile_num=$_POST['mobileNo'];
$latitude=$_POST['latitude'];
$longitude=$_POST['longitude'];
$status=1;
echo $mobile_num;
$sql = "INSERT INTO user (username,mobileNo,latitude,longitude,status ) VALUES (?,?,?,?,?)";
$stmt = $con->prepare($sql);
$stmt>bind_param("sssss",$user_name,$mobile_num,$latitude,$longitude,$status);$result=$stmt->execute(); 

if($result)
    echo "inserted ". $result ." row/rows";
else
    die('Could not connect: ' . $con->error);
mysqli_close($con);
?>

在对值进行硬编码时，代码会正确插入数据，但post方法无法捕获用户名、纬度和经度的值。

这是我的安卓代码：

 @Override
  protected String doInBackground(String... params) {
    try {
        data= URLEncoder.encode("mobileNo","UTF-8")
                 + "="+URLEncoder.encode(mUser.getMobileNo(),"UTF-8");
        data+= URLEncoder.encode("userName","UTF-8")
                + "="+URLEncoder.encode(mUser.getUsername(),"UTF-8");
        data+= URLEncoder.encode("latitude","UTF-8")
                + "="+URLEncoder.encode(String.valueOf(mUser.getLatitude()),"UTF-8");
        data+= URLEncoder.encode("longitude","UTF-8")
                + "="+URLEncoder.encode(String.valueOf(mUser.getLongitude()),"UTF-8");
    } catch (Exception e)
    {
        Toast.makeText(activityContext, "ERROR: "+e, Toast.LENGTH_LONG).show();
    }
    return insertUserData(data);
}

private String insertUserData(String data)
{
    try
    {
        conn = DBConnection.createConnnection(php_file);
        OutputStreamWriter writer = new OutputStreamWriter(conn.getOutputStream());
        writer.write(data);
        writer.flush();
        BufferedReader reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
        response = reader.readLine();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return response;
}

我该怎么办才能解决这个问题？