文件上传不传输文件

Question

好吧，所以即使它说它上传了文件，它也没有做任何事情。定义的路径文件夹非常空。

<?php
    session_start();

    require "assembly/jquery.php";
    require "assembly/user.php";

    $user = new User();

    /* File Upload */
    $target_dir = "img/profiles/";

    $filename = basename($_FILES['fileToUpload']['name']);
    $extension = pathinfo($filename, PATHINFO_EXTENSION);
    $target_file = $user->getUsername().'.'.$extension;

    $uploadValid = 1;

    if(isset($_POST["file_upload_submit"])) {
        $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
        if($check !== false) {
            $uploadValid = 1;
        } 
        else {
            jquery_alert("Unsupported file format");
            $uploadValid = 0;
        }
    }

    // Check file size
    if ($_FILES["fileToUpload"]["size"] > 500000) {
        jquery_alert("Sorry but your file is too large");
        $uploadValid = 0;
    }
    // Allow certain file formats
    if($extension != "jpg" && $extension != "png" && $extension != "jpeg"
    && $extension != "gif") {
        jquery_alert("Invalid file format. Please use only JPG, JPEG, PNG and GIF files.");
        $uploadValid = 0;
    }


    if ($uploadValid == 0) {
        jquery_alert("Something went wrong, please try again");
    } 
    else {
        if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
            jquery_alert($user->getUsername());
            jquery_alert("Your file has been uploaded. Please refresh your browser to view changes.");
        } 
        else {
            jquery_alert("We were unable to upload your file. Please try again");
        }
    }
?>

现在问题是，我没有得到任何错误或任何东西，它只会显示我的名字和它应该的其他信息，但它实际上不会上传文件