如何将价值传递给ASHX？

Question

我制作了一个程序，只需使用“ formData”单击图像本身即可上传图像。但是，我真的不知道formData是什么，也不知道是否可以发送一些字符串。我知道处理程序泛型不接受值。但是以某种方式，如果我发送由Dataform和一个额外的字符串值组成的JSON对象，我可以做到这一点。以下代码显示了使用formData成功上传图片的代码段，只需添加一些字符串值即可对其进行处理。

HTML

<div>
    <img id="img" style="width:300px;height:250px;" src="download.png" />
    <input id="FileUp" hidden="hidden" type="file" /><br />
    <span id="lblMessage" style="color: Green"></span>
</div> 

jQuery

<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script type="text/javascript">
    $(function () {
        var Image = $("#img");
        var FileUpload = $("#FileUp");
        var Label = $("#lblMessage");

        Image.click(function () {
            FileUpload.click().on("change", function () {
                var ObjFile = this.files[0];

                var reader = new FileReader(ObjFile);
                reader.readAsDataURL(ObjFile);
                reader.onload = function (e) {
                    Image.attr('src', e.target.result);

                    var formData = new FormData();
                    formData.append('file', ObjFile);

                    $.ajax({
                        url: 'Handler.ashx',
                        type: 'POST',
                        data: formData, // <-- here I would like to send string value alongside formData
                        cache: false,
                        contentType: false,
                        processData: false,
                        success: function (file) {
                            Label.html("<b>(" + file.name + ")</b> ... has been uploaded successfully.");
                        },
                        xhr: function () {
                            var fileXhr = $.ajaxSettings.xhr();
                            if (fileXhr.upload !== true) {
                                return fileXhr;
                                alert("Sorry, your file wasn't uploaded !!");
                            }
                        }
                    });
                };
            });
            return false;
        });
    });
</script>

ASHX处理程序

    public void ProcessRequest(HttpContext context)
    {
        //Check if Request is to Upload the File.
        if (context.Request.Files.Count > 0)
        {
            //Fetch the Uploaded File.
            HttpPostedFile postedFile = context.Request.Files[0];

            //Set the Folder Path.
            string folderPath = context.Server.MapPath("~/Uploads/");

            //Set the File Name.
            string fileName = Path.GetFileName(postedFile.FileName);

            //Save the File in Folder.
            postedFile.SaveAs(folderPath + fileName);

            //Send File details in a JSON Response.
            string json = new JavaScriptSerializer().Serialize(
                new
                {
                    name = fileName
                });
            context.Response.StatusCode = (int)HttpStatusCode.OK;
            context.Response.ContentType = "text/json";
            context.Response.Write(json);
            context.Response.End();
        }
    }