Ajax不执行成功函数

我发现了问题所在：

1. 首先，我将ContentType指定为json，同时将其作为字符串，所以我不得不改变它。

2. 其次，我使用$_POST的Is_set andis_empty函数我肯定得到了POST字段。

3. 最后，由于某种原因，返回的ajax变量数据不会显示出来by键，因此data.success未定义，但data返回所有输出从php文件

我仍在试图弄清楚为什么我不能按键访问返回的JSON。如果你有任何建议，请告诉我，我不想再提出另一个问题。以下是工作代码：

$(document).ready(function(){
    $("form#loginForm").submit(function() {
    // loginForm is submitted
        var username = $('#username').attr('value'); // get username
        var password = $('#password').attr('value'); // get password
        console.log(username + password) ;
        if (username && password) { // values are not empty
            $.ajax({
                type: "POST",
                url: "https://xxx/login.php", // URL of the Php script
                contentType: "application/x-www-form-urlencoded; charset=utf-8",
                dataType: "application/json", //expected from server in response
                // send username and password to the Php script
                //data: "username=" + username + "&password=" + password,
                data:'username='+ username+'&password='+ password,
                error: function(XMLHttpRequest, textStatus, errorThrown) { // script call was *not* successful
                    $('div#loginResult').text("responseText: " + XMLHttpRequest.responseText
                    + ", textStatus: " + textStatus
                    + ", errorThrown: " + errorThrown);
                    $('div#loginResult').addClass("error");
                },
                success: function(data){

                    $('form#loginForm').hide();
                    $('div#loginResult').text("Login: " + data );
                    $('div#loginResult').addClass("success");
                                                                }

            });
        }
        else {
            $('div#loginResult').text("enter username and password");
            $('div#loginResult').addClass("error");
        } // else
        $('div#loginResult').fadeIn();
        return false;
    });
})

Login.php

<?php
if (isset($_POST["username"]) && !empty($_POST["username"])) {
    $username = $_POST["username"];}
if (isset($_POST["password"]) && !empty($_POST["password"])) {
    $password = $_POST["password"];}
$dbhost = 'xxx';
$dbuser = 'xxxxxx';
$dbpass = 'xxxxxxxx';
$conn = mysql_connect($dbhost, $dbuser, $dbpass); // connect to server
if(! $conn )
{
    die('Could not connect: ' . mysql_error());
}
mysql_select_db('sl493',$conn);
$query = mysql_query("SELECT *FROM metauser WHERE metauser.username = '$username'AND metauser.password = '$password'") or die(mysql_error()); //select data from metauser table
$row = mysql_fetch_assoc($query);

if($row['username'] == $username)
{
        if($row['usertype']== 'student')
              { $type = 'student'; }
                    else{ $type = 'admin'; }
    //$arr = array('result' => 'loginOK', 'usertype' => $type);
    $associativeArray = array();
    $associativeArray ['result'] = 'success';
    $associativeArray ['usertype'] = $type;
    //$arr = '{"success":"login is successful"}';
    //echo $type;
    echo json_encode($associativeArray); }

else
{$arr = '{"error":"username or password is wrong"}';
    echo json_encode($arr);}
?>

试试这个：

var data="";
data=['username':username,'password':password];//Add this
 $.ajax({
            type: "POST",
            url: "url", // URL of the Php script
            contentType: "application/json; charset=utf-8",
            dataType: "json", //expected from server in response
            // send username and password to the Php script
            data: JSON.stringify(data),//Stringify your data while sending
            success: function(data){ //script was successful, data contains response from mysql database
                if (data.error) { // login was not successful
                    $('div#loginResult').text("data.error: " + data.error);
                    $('div#loginResult').addClass("error");
                } // if
                else { // login was successful
                    $('form#loginForm').hide();
                    $('div#loginResult').text("data.success: " + data.success);
                    $('div#loginResult').addClass("success");
                } //else
            },
            error: function(XMLHttpRequest, textStatus, errorThrown) { // script call was *not* successful
                $('div#loginResult').text("responseText: " + XMLHttpRequest.responseText
                + ", textStatus: " + textStatus
                + ", errorThrown: " + errorThrown);
                $('div#loginResult').addClass("error");
            }, // success
        }); // ajax