$(document).ready(function () {
    $(".submit_btn").click(function (event) {
        event.preventDefault();
        var form = $('#fileUploadForm')[0];
        var data = new FormData(form);
        data.append("CustomField", "This is some extra data, testing");
        $("#btnSubmit").prop("disabled", true);
        $.ajax({
            type: "POST",
            enctype: 'multipart/form-data',
            url: "upload.php",
            data: data,
            processData: false,
            contentType: false,
            cache: false,
            timeout: 600000,
            success: function (data) {
                console.log();
            },
        });
    });
});

View:
<label class="btn btn-info btn-file">
Import <input type="file" style="display: none;">
</label>
<Script>
$(document).ready(function () {
                $(document).on('change', ':file', function () {
                    var fileUpload = $(this).get(0);
                    var files = fileUpload.files;
                    var bid = 0;
                    if (files.length != 0) {
                        var data = new FormData();
                        for (var i = 0; i < files.length ; i++) {
                            data.append(files[i].name, files[i]);
                        }
                        $.ajax({
                            xhr: function () {
                                var xhr = $.ajaxSettings.xhr();
                                xhr.upload.onprogress = function (e) {
                                    console.log(Math.floor(e.loaded / e.total * 100) + '%');
                                };
                                return xhr;
                            },
                            contentType: false,
                            processData: false,
                            type: 'POST',
                            data: data,
                            url: '/ControllerX/' + bid,
                            success: function (response) {
                                location.href = 'xxx/Index/';
                            }
                        });
                    }
                });
            });
</Script>
Controller:
[HttpPost]
        public ActionResult ControllerX(string id)
        {
            var files = Request.Form.Files;
...

为了正确使用表单数据，您需要执行2个步骤。

准备工作

您可以将整个表单交给FormData()进行处理

var form = $('form')[0]; // You need to use standard javascript object here
var formData = new FormData(form);

或为FormData()指定确切的数据

var formData = new FormData();
formData.append('section', 'general');
formData.append('action', 'previewImg');
// Attach file
formData.append('image', $('input[type=file]')[0].files[0]); 

发送表单

使用jquery的Ajax请求是这样的:

$.ajax({
    url: 'Your url here',
    data: formData,
    type: 'POST',
    contentType: false, // NEEDED, DON'T OMIT THIS (requires jQuery 1.6+)
    processData: false, // NEEDED, DON'T OMIT THIS
    // ... Other options like success and etc
});

之后，它会发送ajax请求，就像你提交普通表单一样，enctype="multipart/form-data"

更新:此请求不能在选项中没有类型:“POST”，因为所有文件都必须通过POST请求发送。

注意:contentType: false仅在jQuery 1.6以后可用

实际上，文档显示您可以使用XMLHttpRequest().send() 简单地发送多种形式的数据 以防jquery很烂

$('#form-withdraw').submit(function(event) {

    //prevent the form from submitting by default
    event.preventDefault();



    var formData = new FormData($(this)[0]);

    $.ajax({
        url: 'function/ajax/topup.php',
        type: 'POST',
        data: formData,
        async: false,
        cache: false,
        contentType: false,
        processData: false,
        success: function (returndata) {
          if(returndata == 'success')
          {
            swal({
              title: "Great",
              text: "Your Form has Been Transfer, We will comfirm the amount you reload in 3 hours",
              type: "success",
              showCancelButton: false,
              confirmButtonColor: "#DD6B55",
              confirmButtonText: "OK",
              closeOnConfirm: false
            },
            function(){
              window.location.href = '/transaction.php';
            });
          }

          else if(returndata == 'Offline')
          {
              sweetAlert("Offline", "Please use other payment method", "error");
          }
        }
    });



}); 

我不能在上面加上评论，因为我没有足够的声誉，但上面的答案对我来说几乎是完美的，除了我必须加上

类型:“文章”

到.ajax调用。我挠了几分钟的头，试图弄清楚我做错了什么，这就是它所需要的，而且是一种治疗。这是整个片段:

完全归功于上面的答案，这只是一个小调整。这只是为了防止其他人被困住，看不到显而易见的东西。

  $.ajax({
    url: 'Your url here',
    data: formData,
    type: "POST", //ADDED THIS LINE
    // THIS MUST BE DONE FOR FILE UPLOADING
    contentType: false,
    processData: false,
    // ... Other options like success and etc
})