使用PHP验证进行AJAX文件上载

I have a form that has two text fields and a file upload field.

The validation is handled completely from PHP and I'm using a little bit of Ajax to retrieve the error messages the PHP script produces via an array (err[]).

My problem is, I can't seem to get the file upload validation to work correctly. (when uploading a file, it will always say "Wrong file format only .png , .gif, .jpg, .jpeg are accepted")

The Ajax is below:

function checkform() {
        $.post('upload.php', $("form#uploadForm").serialize(), function (data) {

                $("div#error").html(data).slideDown("fast");

                var destination = $('div#uploadContainer').offset().top - 15;
                $("html:not(:animated),body:not(:animated)").animate({
                    scrollTop: destination
                }, 200);

            });
    return false;
}

The following validation seems to ALWAYS be triggered:

$extension = strrchr($_FILES['uploadFile']['name'], '.');
    if (!in_array($extension, $extensions)) {
        $err[]='Wrong file format only .png , .gif, .jpg, .jpeg are accepted';
    }
...
...

if (isset($_FILES['uploadFile']) && $_FILES['uploadFile']['size'] != 0)
{
    // Upload file
}

$extension = end(explode('.', $_FILES['uploadFile']['name']));

if (!in_array($extension, $extensions))
{
    $err[]='Wrong file format only .png , .gif, .jpg, .jpeg are accepted';
}

As $extension has extension without dot(.). Remove dot(.) from file extensions

$extensions = array('.png', '.gif', '.jpg', '.jpeg','.PNG', '.GIF', '.JPG', '.JPEG');

which will be

$extensions = array('png', 'gif', 'jpg', 'jpeg','PNG', 'GIF', 'JPG', 'JPEG');

Hope this fixes the bug

Per @riddell's comment (AJAX File Upload with PHP Validation)

the problem is most likely NOT php but actually the Jquery itself. something like this could work

var form = $('form')[0];
var data = new FormData(form);

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

Correct logic for upload and checking file extension

if (isset($_FILES['uploadFile']) && $_FILES['uploadFile']['size'] != 0)
{
    $extension = end(explode('.', $_FILES['uploadFile']['name']));

    if (!in_array($extension, $extensions))
    {
        $err[]='Wrong file format only .png , .gif, .jpg, .jpeg are accepted';
    }

    // Write code to upload image here
}
else
{
    // There was error while uploading image
    // $_FILES['uploadFile']['error'] gives error code
    //  
    // Possible errors
    // UPLOAD_ERR_OK: 0
    // UPLOAD_ERR_INI_SIZE: 1
    // UPLOAD_ERR_FORM_SIZE: 2
    // UPLOAD_ERR_NO_TMP_DIR: 6
    // UPLOAD_ERR_CANT_WRITE: 7
    // UPLOAD_ERR_EXTENSION: 8
    // UPLOAD_ERR_PARTIAL: 3
}