$ .ajax POST不发布

This is exactly what the title describes, when I hit submit, and use php file to echo the result its empty.

$( "form#fileupload" ).on( "submit", function( event ) {
  event.preventDefault();
  var formData = $( 'form#fileupload' ).serialize();
  $.ajax({
    url: 'create_adgroup.php',
    type: 'POST',
    data: formData,
    async: false,
    cache: false,
    contentType: false,
    processData: false,
    success: function (returndata) {
      $("#footer").html(returndata);
    }
  });

  return false;
});

and the php is as such:

ECHO "PRINT POST: ".print_r($_POST);
echo "le titre: ".$_POST['title'];

any suggestions please the alert returns the serialized string and it has all the data and title is one of them.

Try with this, usually i did the ajax POST with this kind of code:

$( "form#fileupload" ).on( "submit", function( event ) {
  $.post('create_adgroup.php', $('form#fileupload').serialize(), function(data) {
    $('#footer').html(data);
  });

  event.preventDefault();  
  return false;
});

For uploading file using ajax I prefer using jquery.form.js plugin. Reference