Establishing the httppostedfilebase variable when validation is unsuccessful in an ASP.Net MVC view

I'm currently facing an issue with handling validation errors in my application. I have implemented uploading and downloading images successfully, but when there are validation errors and the controller redirects back to the page, the HttpPostedFileBase object becomes empty. This means that the user has to re-upload the image, which is less than ideal. Is there a way to reload the image into HttpPostedFileBase without requiring the user to upload it again?

In my controller, I've attempted to set the HttpPostedFileBase back to the returned HttpPostedFileWrapper, but this approach doesn't work on subsequent postbacks. The object remains empty, even after resubmitting the form.

[HttpPost]
    public ActionResult Edit(EditStudentViewModel studentViewModel)
    {
        if (ModelState.IsValid)
        {
            //do stuff here
        } else
        {
            var years = Enumerable.Range(DateTime.Now.Year - 99, 100).Reverse();
            studentViewModel.Years = years.Select(c => new SelectListItem
            {
                Text = c.ToString(),
                Value = c.ToString(),
                Selected = (c == studentViewModel.SelectedYearId)
            });
            studentViewModel.StudentImageResult =
                new FileContentResult(
                    System.IO.File.ReadAllBytes(
                        System.IO.Path.GetFullPath(Server.MapPath("~/App_Data/Images/no_image.jpg"))),
                    "image/jpeg");
            // Resetting httppostedfilewrapper here doesn't work
            studentViewModel.HttpPostedFileBase= studentViewModel.StudentImageFileBase;
            return View(studentViewModel);
        }
    }

Answer №1

It is not possible to set the value of a file-upload in HTML or through JavaScript. This limitation exists to prevent potential security risks, such as uploading harmful files without user consent.

One alternative approach is to perform validation using JavaScript before submitting the form. This method eliminates the need for a Post-Back and provides a more user-friendly experience.

If validation fails, you can still save the uploaded file, display its name in a label, and store the image's id or uid in a hidden input field for reference.

Answer №2

When the validation fails, one approach could be to temporarily store the file on the server and display the image using

@Html.Image("Name", Url.Content("~/Images/TempLocation/temp.jpg"), "Picture")

Upon re-posting, if the model is valid, you can then save the "temp.jpg" from the temporary location into your application.

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