我不能从php页面检索JSON数据数组到另一个

<?php
require_once './db_connect.php';
    $db = new DB_Connect();
    $db->connect();
$data = json_decode($_POST['myData']);
 $array=json_decode($_REQUEST['question']);

 if(isset($_POST['myData'])){
 $obj = json_decode($_POST['myData']);
 //some php operation

 $q = "insert into questions(question)
    values ('". $obj."')";

    $result = mysql_query($q) or die(mysql_error());
}
?>

我想检索JSON数据是从另一个php页面发送到这个页面，但我只是不能，，为什么呢?

这是另一页

    function validateForm()
    {
        var q = document.forms["form1"]["question"].value;
        var T = document.forms["form1"]["title"].value;
        if (T == null || T == "")
        {
            alert("please type you form title first");
            return false;
        }
        if (q == null || q == "")
        {
            document.getElementById("question").style.color="black";
            alert("please enter your question");
            return false;
        }
        question.push(q);
        //alert(JSON.stringify(question));
        var xhr = new XMLHttpRequest();
xhr.open('post', 'create_form.php',true);
// Track the state changes of the request
xhr.onreadystatechange = function(){
    // Ready state 4 means the request is done
    if(xhr.readyState === 4){
        // 200 is a successful return
        if(xhr.status === 200){
            alert(xhr.responseText); // 'This is the returned text.'
        }else{
            alert('Error: '+xhr.status); // An error occurred during the request
        }
    }
}
// Send the request to send-ajax-data.php
xhr.send({myData:JSON.stringify(question)}); //+encodeURI(JSON.stringify(question))
      //  addField();
        return true;
    }

谁能帮帮我??我尝试用jquery来解决这个问题，ajax，都是一样的，这就是为什么我尝试只用javascript来解决这个

$json = file_get_contents('php://input');
$obj = json_decode($json, TRUE);

$data = json_decode($_POST['myData']);
 $array=json_decode($_REQUEST['question']);

 if(isset($_POST['myData'])){
 $obj = json_decode($_POST['myData']);