如何强制服务器响应为json

Question

我在StreamBuilder的Flutter应用中遇到了Geting data from mysql to StreamBuilder Flutter的问题，>

现在我要强制服务器将数据作为JSON传递给我的PHP代码db.php

<?php

$dns = 'mysql:host=localhost;dbname=id13424627_flutter';
$user = 'id13424627_flutter_app';
$pass = 'Flutter_maen12';

try{
  $db = new PDO ($dns, $user, $pass);
  echo 'connected';
}catch( PDOException $e){
    $error = $e->getMessage();
    echo $error;
}
get.php

<?php
require_once('db.php');
$query = 'SELECT * FROM flutter';
$stm = $db->prepare($query);
$stm->execute();
$row = $stm->fetch(PDO::FETCH_ASSOC);
echo json_encode($row);

<<

尝试删除此echo 'connected';并添加get.php文件的顶部；