一个简单的登录画面,选择部门后,筛选该部门的用户,写这个getuser.php文件的时候，如果采用include "conn.php";这种方式连接数据库的话,电脑上测试是能读到用户给picker的,但是测试版或者真机调试时,picker只能读出一堆null了,但是真机调试,在Network菜单下看到数据确实已经取到了。如果把连接写死在这个文件里,就完全没问题。很疑惑,请帮忙看看.因为好些个文件都有类似错误,所以得改动多个文件比较麻烦,所以来求助大家 以下这样出错: include "conn.php"; if (!$con){  die('Could not connect: ' . mysqli_connect_error());}  mysqli_query($con,"set names utf8");  $dept = $_GET['dept']; $grade=$_GET['grade'];    $sql1="  select * from user   where dept='$dept' and grade=1 order by username ;"; $result1 = mysqli_query($con,$sql1);  $data=$result1->fetch_all(PDO::FETCH_LAZY); echo json_encode($data); mysqli_close($con); 以下这样没问题: header("Content-Type: text/html;charset=utf-8");  $con=mysqli_connect("150.xx.xx.xx","wx","xxxxxxxx","xxx"); if (!$con){  die('Could not connect: ' . mysqli_connect_error());}  mysqli_query($con,"set names utf8");  $dept = $_GET['dept']; $grade=$_GET['grade'];    $sql1="  select * from user   where dept='$dept' and grade=1 order by username ;"; $result1 = mysqli_query($con,$sql1);  $data=$result1->fetch_all(PDO::FETCH_LAZY); echo json_encode($data); mysqli_close($con); conn.php如下: header("Content-Type: text/html;charset=utf-8");  $con=mysqli_connect("150.xx.xx.xx","wx","xxxxxxx","xxx"); if (!$con) { die('Could not connect: ' . mysqli_connect_error()); } mysqli_query($con,"set names utf8"); 写picker部分是这样:    success: function (res) {                var array = res.data; //         var username = [];         var length = array.length;         for (var i = 0; i < length; i++) {           username.push(array[i].username)         }         if (username.length > 0) {           userpick = username[userindex];         }          that.setData({           array: array,           username: username,           userindex: userindex         })        }

php版本是7.2,出现了如下错误 Use of undefined constant XXXXXXX - assumed 'XXXXX' (this will throw an Error in a future version of PHP)  网上查了些，可能要将PHP版本降成5.6，或者装多个版本PHP切换也可以， Warning: Use of undefined constant datelist - assumed 'datelist' (this will throw an Error in a future version of PHP) in C:\xampp\htdocs\stbc\apply.php on line 6  PHP第六行很简单 就是：$datelist=$_POST[datelist];