如何使用ajax将选定的选项发送到php文件？

I'm trying to get selected option in php to save it in a database. I'm using Ajax and it sends data and a file all together with FormData. Everything goes ok but when I select an option and click on submit button, the php file does not get nothing and just saves input text data and file information.

HTML

<form id="data" method="post" enctype="multipart/form-data">
     <input type="text" name="first"/>
     <input type="file" name="image"/>
     <select name="disp" id="dispnb" class="dispc">
            <option value="0" selected>Select...</option>
            <option value="2"><b>Option A</b></option>
            <option value="3">Option B</option>
            <option value="3">Option C</option>
     </select>
</form>

jQuery

$(document).ready(function(){
    $("form#data").submit(function(){
    var formData = new FormData($(this)[0]);

    $.ajax({
        url: 'upload.php',
        type: 'POST',
        data: formData,
        async: false,
        success: function (data) {
            alert(data)
        },
        cache: false,
        contentType: false,
        processData: false
    });

    return false;
});          
});

PHP

<?php
    echo $_POST['first'];
    echo $_POST['disp'];
    echo $_FILES['image']['name'];
?>

Try like this:

$("#dispnb").change(function(){
var your_selected_value = $('#dispnb').val();
$.ajax({
type: "POST",
url: 'upload.php',
data: {"selected": your_selected_value},
success: function(data) {
 alert(data);
},
error: function(data) {
// Stuff
}
});
});

In upload.php

<?php
if (isset($_POST['selected'])){
$a = $_POST['selected'];
echo $a;
}

You can use $('form').serialize(); instead of var formData = new FormData($(this)[0]);

Using this code you will get all from data.

add id to your text fields

<input type="text" name="first" id="first"/>
<input type="file" name="image" id="image"/>

js

$(document).ready(function(){
    $("form#data").submit(function(){
    var data = array{}
    data.disp = $('#dispnb').val();
    data.first = $('#first').val();
    data.image = $('#image').val();

    $.ajax({
        url: 'upload.php',
        type: 'POST',
        data: data,
        async: false,
        success: function (data) {
            alert(data)
        },
        cache: false,
        contentType: false,
        processData: false
    });

    return false;
});          

Then in ur php file

<?php
    echo $_POST['first'];
    echo $_POST['disp'];
    echo $_FILES['image']['name'];
?>
});