How do I prevent IE save file dialog when using fileupload in asp.net mvc

Question

When I try and upload a file using ASP.NET MVC it works fine in FF && Chrome, but in IE and Opera a dialog pops-up which asks me to either download, save or cancel.

Choosing either of the options, prevents the fileupload from working. How can I get round this problem?

 public class ImportModel
    {                     
        [Required]
        [FileExtensions("csv", ErrorMessage = "Please upload a valid .csv file")]
        public HttpPostedFileBase File { get; set; }
    }



[HttpPost]
    public virtual ActionResult StartImport(ImportModel model = null)
    {
        if (model != null)
        {
            var status = _importService.StartImport(model);
            return Json(status, JsonRequestBehavior.AllowGet);
        }
        return null;
    }

View code below (summarised):

<div id="dlgImport" class="hidden">

        @using (Html.BeginForm(MVC.Import.StartImport(), FormMethod.Post, new { @class = "smallForm", id = "frmImport", enctype = "multipart/form-data" }))
        {            
            <div class="fields-inline">
                <div class="editor-label">
                    @Html.Label("File")
                </div>
                <div class="editor-field">
                    @Html.TextBoxFor(x => x.File, new { @class="input-file", type = "file" })
                    @Html.ValidationMessageFor(x => x.File)
                </div>              
            </div>
        }
    </div>

</div>



$(function() {
        $("#frmImport").ajaxForm({
            success: function (responseHtml) {
                // response is wrapped in pre tags by the browser - the ajax upload is carried out using an iframe                                                
                var response = $.parseJSON($(responseHtml).text());
            }
        });
});


 var vm = {

        startImport: function () {

            if ($("#frmImport").valid()) {                
                $("#frmImport").submit();
            }
        }

    }

Answer 1

Now that you have posted your code it looks like that you are using the jquery form plugin. As explained in the documentation this plugin supports file uploads using AJAX but you cannot return JSON from your server side script:

Since it is not possible to upload files using the browser's XMLHttpRequest object, the Form Plugin uses a hidden iframe element to help with the task. This is a common technique, but it has inherent limitations. The iframe element is used as the target of the form's submit operation which means that the server response is written to the iframe. This is fine if the response type is HTML or XML, but doesn't work as well if the response type is script or JSON, both of which often contain characters that need to be repesented using entity references when found in HTML markup.

To account for the challenges of script and JSON responses, the Form Plugin allows these responses to be embedded in a textarea element and it is recommended that you do so for these response types when used in conjuction with file uploads. Please note, however, that if there is no file input in the form then the request uses normal XHR to submit the form (not an iframe). This puts the burden on your server code to know when to use a textarea and when not to.

So basically your upload controller action should respond with:

<textarea>{"foo":"bar"}</textarea>

instead of:

{"foo":"bar"}

Also you should not use the application/json response content type in this case.

You could write a custom action result to achieve that:

public class FileJsonResult : JsonResult
{
    public FileJsonResult(object data)
        : base()
    {
        Data = data;
        JsonRequestBehavior = JsonRequestBehavior.AllowGet;
    }

    public override void ExecuteResult(ControllerContext context)
    {
        context.HttpContext.Response.Write("<textarea>");
        base.ExecuteResult(context);
        context.HttpContext.Response.Write("</textarea>");
        context.HttpContext.Response.ContentType = "text/html";
    }
}

and then:

[HttpPost]
public virtual ActionResult StartImport(ImportModel model = null)
{
    if (model != null)
    {
        var status = _importService.StartImport(model);
        return new FileJsonResult(status);
    }
    new FileJsonResult(new { status = false, errorMessage = "The model was null" });
}

Now you might also need to adapt your success handler to strip the <textarea> tags:

$('#frmImport').ajaxForm({
    success: function (responseHtml) {
        var responseHtml = responseHtml
            .replace(/\<textarea\>/i, '')
            .replace(/\<\/textarea\>/i, '');
        var response = $.parseJSON(responseHtml);
        // do something with the response
    }
});