How to check null value within TempData Razor MVC that written inside js code

Question

I'm Trying to check null value within TempData Razor MVC that written inside javascript code, but unfortunately it doesn't work.

whether TempData value is null or not, the condition is always true

if ('@TempData["Error"]' != null) {
    alert("Problem" + '\n' + "@TempData["error"]");
} else {
    alert("The file Uploaded Successfully");    
}

How i can check? if there are alternatives, please let me know.

thanks.

Edit:

The code above is part of JQuery ajax request code.

 <script>
    $body = $("body");
    $(document).on({
        ajaxStart: function () { $body.addClass("loading"); },
        ajaxStop: function () { $body.removeClass("loading"); }
    });

    $(document).ready(function () {
        $("#upload").click(function () {
            var data = new FormData();

            //Add the Multiple selected files into the data object
            var files = $("#files").get(0).files;
            for (i = 0; i < files.length; i++) {
                data.append("files" + i, files[i]);
            }
            //data.append("id", '');
            data.append("id", '@Model.NoteID');
            //Post the data (files) to the server

            if (files.length > 0) {
                $.ajax({
                    type: 'POST',
                    url: "@Url.Action("Upload","Files")",
                    data:data,
                    contentType: false,
                    processData: false,
                    success: function (data) {
                        if ('@TempData["Error"]' != null) {
                            alert("Problem" + '\n' + "@TempData["error"]");
                        } else {
                            alert("file uploaded successfully");
                        }
                    },
                    error: function () {
                        alert("Fail");
                    },
                });
            }
        });
    });
</script>

No, it is inside HTML page. Actually the code above is part of JQuery ajax request, i will update the post. — askm, Feb 16 '17 at 05:04
Refer updated answer based on your edit and the fact this is inside an ajax call. — , Feb 16 '17 at 05:16

score 4 · Accepted Answer · 2017-02-16T05:16:00.477

4

Your quoting the value, so if @TempData["Error"] is null, it translates to a empty string. You could check it using .length but it would be better to use

var error = @Html.Raw(Json.Encode(TempData["Error"]))
if (error) {
    alert("Problem" + '\n' + error);
} else {
    alert("The file Uploaded Successfully");
}

Based on the revised context of the question, your using this inside an ajax call. Razor code is parsed on the server before its sent to the view, so @TempData["Error"] returns the value when when the page is first rendered. Just because you may be setting the value of TempData in the Upload() method does not update it.

Your method should be returning json containing the error so that you can then display it in the success callback. For example, your method might be

public ActionResult Upload(...)
{
    return Json(null); // to indicate success, or
    return Json("oops, something went wrong);
}

and then in the ajax callback

success: function (response) {
    if (response) {
        alert(response);
    } else {
        alert("The file Uploaded Successfully");
    }

edited Feb 16 '17 at 05:16

answered Feb 16 '17 at 04:59

It works, but when the request ends successfully with return json(null) .. it returns 'Fail'. it goes to error:function(){alert("Fail");} – askm Feb 16 '17 at 06:47
That should not happen unless you throw an exception (although it does with the `$.getJSON()` method). You can always do something like `return Json(true);` for success and `return Json( new { Error = "your error message" });` and then in the script - `if (response.Error) { alert(response.Error); } else { ... }` – Feb 16 '17 at 06:53
And did you happen to add `dataType: 'json',` (which would also cause the error - if so just delete it) – Feb 16 '17 at 06:57
I added dataType:'json', then delete it .. same problem happened. fortunately, i found good solution for me. thank you so much for your help. – askm Feb 16 '17 at 08:08

How to check null value within TempData Razor MVC that written inside js code

1 Answers1