I am working through Telerik's UI for ASP.NET Core tutorial on YouTube ... RPSTrackerASPCore ... and I am at the point where the instructor is walking us through adding an Upload component to the project. I am using a much more recent version of Kendo UI so I have to tweak some things to get them to work properly. So far that hasn't been a problem. But the Upload component has me stumped.

The VS projects are .Net 9.0.

I am using Telerik.UI.for.AspNet.Core (2026.1.325) and I am loading the JavaScript assets as ECMAScript modules. So here is the list of modules I am currently loading:

<script src="~/lib/kendo-ui/mjs/kendo.core.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.button.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.textbox.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.textarea.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.slider.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.tabstrip.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.dataviz.chart.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.grid.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.tilelayout.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.upload.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.draganddrop.js" type="module"></script>
<script src="~/lib/kendo-ui/mjs/kendo.aspnetmvc.js" type="module"></script>

And here is my component definition:

            @(Html.Kendo().Upload()
                .Name("files")
                .Multiple(true)
                .Async(a => a
                    .Save("SaveAttachmentsAsync", "Upload")
                    .AutoUpload(true)
                )
                .Validation(v => v.AllowedExtensions(new string[] { ".jpg", ".png", ".jpeg" }).MaxFileSize(10485760))
            )

And here is the inline JavaScript generated by the component:

<script type="module">kendo.syncReady(function(){jQuery("#files").kendoUpload({"async":{"autoUpload":true,"saveUrl":null},"multiple":true,"validation":{"allowedExtensions":[".jpg",".png",".jpeg"],"maxFileSize":10485760}});});</script>

I include this because I think it is odd that the async.saveUrl parameter is set to null.

I can use the "Select Files" button to select a file, and they do get added to the file list, but the autoupload functionality is not triggered. And there are no errors in the console. And the drag-and-drop functionality is not active. If I drag an acceptable file over the component the file (an image) just gets opened in a new browser tab.

I have breakpoints in my UploadController.SaveAttachmentsAsync method but they are never hit.

If I submit the form and break on the method that handles the page's form post request I DO see the file included in the request, so at least that part does actually work.

But none of the additional Kendo functionality seems to work. I thought perhaps I am missing an ECMAScript module that needs to be loaded but the documentation doesn't mention any. There are no errors in the browser console so there doesn't seem to be a JavaScript problem happening.

I did replace the modules with the standard vanilla kendo.all.min.js and kendo.aspnetmvc.min.js scripts but I get the exact same behavior.

So what am I missing?

I'm attempting to use the Kendo Upload control asynchronously to an MVC controller, which passes the file to a WebApi controller.  The file is uploaded successfully, however when it returns to the MVC view, it reports that the file failed to upload with the error below.  We are using Azure B2C for authentication:

"Access to XMLHttpRequest at 'https... b2clogin.com...' (redirected from 'https//localhost:7074/Files/UploadFile') from origin 'https://localhost:7074' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource."

Server response:

"Failed to load resource: net::ERR_FAILED"

The control is located in a partial view as part of a tab control on a CSHTML view.  Here is the code for the upload control:

<div class="row">
    <div class="col-md-8">
        @(Html.Kendo().Upload()
                .Name("uploadedFile")
            .Multiple(false)
            .Validation(v =>
            {
                v.AllowedExtensions(new string[] { ".csv" });
                v.MaxFileSize(3145728);
            })
            .Async(a => a
                .AutoUpload(false)
                .Save("UploadFile", "Files")
            )
            .Events(e =>
            {
    e.Upload("onFileUpload");
            })

         )
    </div>
    <div class="col-md-4">
    </div>

</div>

Here is the C# code for the MVC controller:

        [HttpPost]
        public async Task<ActionResult> UploadFile(IFormFile uploadedFile, string month, string year)
        {
            if (uploadedFile == null || uploadedFile.Length == 0)
                return BadRequest("No file uploaded.");

            var reportingPeriod = month + year;

            using (var content = new MultipartFormDataContent())
            {
                if (uploadedFile.Length > 0)
                {
                    var streamContent = new StreamContent(uploadedFile.OpenReadStream());
                    streamContent.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue(uploadedFile.ContentType);
                    content.Add(streamContent, "file", uploadedFile.FileName);
                }

                using (var response = await _client.HttpClient.PostAsync("/api/Files/loadbackdatedmonthlytrueupfile/" + reportingPeriod, content))
                {
                    if (response.IsSuccessStatusCode)
                    {
                        // Kendo expects an empty string for success
                        return Content("");
                    }
                    else
                    {
                        return StatusCode((int)response.StatusCode, await response.Content.ReadAsStringAsync());
                    }

                }

            }
        }

Here is the code for the WebApi controller:

{

     //other logic here

     return Ok(new { file.FileName, file.Length });

}

This is the info I received from Copilot:

How can I configure this upload control to return to the view without the error (attaching screenshot)?

Hi, I'm referring to the article below:

https://www.telerik.com/aspnet-core-ui/documentation/html-helpers/editors/upload/modes-of-operation#asynchronous-mode-fallback

In the article Asynchronous Mode Fallback is When Upload which is placed inside a form and configured for asynchronous operation.

I have done this, however after uploading some file (and failed since I didn't implement the controller) the form post still doesn't contain any Files.

Is there a specific to implement a fallback mechanism? a sample will be very helpful.

Hello, I hope you are well.

I hope you can help me with this problem I have.

I am using the Kendo UI for JQuery Upload.

What I require is to upload an entire folder of TXT files, but I have a routine that validates that the name and content meet certain rules.

I apply these rules within the foreach loop (var file in files), because what is required is that if the file is valid it shows a text that it is valid, otherwise it shows a text that is not valid and for both options to continue processing the next file.

But by marking that file as erroneous, the controller is exited and the view is returned, thus leaving the processing of the rest of the files incomplete.

I share the code of the view and the controller, hoping you can give me some light.

View Code:

<div class="centered">
    @using Kendo.Mvc.UI
    <div>
        <div class="demo-section">
            @(Html.Kendo().Upload()
                .Name("files")
                .Async(a => a
                    .Save("ChunkSave", "Upload")
                    .Remove("Chunk_Upload_Remove", "Upload")
                    .AutoUpload(true)
                    .ChunkSize(11000)

                )
                .Multiple(true) // Enable multiple file selection
                    .Directory(true)
                    .DirectoryDrop(true)
                .Validation(validation =>
                {
                    //validation.MaxFileSize(20000000);
                })
                .Events(events =>
                {
                    events.Upload("onUpload");
                    events.Success("onUploadSuccess");
                    events.Error("onUploadError");
                    events.Select("onSelect");
                })
                .Messages(messages =>
                {
                    messages
                        .Select("Seleccionar archivos")
                        .DropFilesHere("Suelta archivos aquí para cargarlos")
                        .Remove("Eliminar")
                        .Retry("Reintentar")
                        .StatusFailed("Error")
                        .StatusUploaded("Terminado")
                        .StatusUploading("Cargando")
                        .UploadSelectedFiles("Cargar archivos")
                        .UploadFail("Error al procesar el archivo.")
                        .HeaderStatusUploaded("Terminado");
                })

            )
        </div>
    </div>
</div>

Controller Code:

public async Task<ActionResult> ChunkSave(IEnumerable<IFormFile> files, string metaData, string cve)
{

    int status = 0;
    DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(ChunkMetaData));


    MemoryStream ms = new MemoryStream(Encoding.UTF8.GetBytes(metaData));
    ChunkMetaData? somemetaData = serializer.ReadObject(ms) as ChunkMetaData;
    string path = String.Empty;

    if (files != null)
    {
        foreach (var file in files)
        {
            cap_dbt controller = new cap_dbt(_context);
            controller.ProcessFile(file, somemetaData.FileName, cve);
            status = controller.ProcessFile(file, somemetaData.FileName, cve);
            if (status == 1)
            {
                Upload(files, somemetaData.FileName);
            }
        }
    }


    if (somemetaData is null)
    {
        throw new Exception("No Metadata!");
    }

    Util.FileResult fileBlob = new Util.FileResult();
    fileBlob.uploaded = somemetaData.TotalChunks - 1 <= somemetaData.ChunkIndex;
    fileBlob.fileUid = somemetaData.UploadUid;
    fileBlob.warnings = Mensajes.msgLoadCsvWarning;
    fileBlob.message = "[" + somemetaData.FileName + "]\t";

    try
    {
        if (!fileBlob.uploaded)
        {
            fileBlob.message += "[ERROR]" + Mensajes.msgLoadCsvError;

            return StatusCode(500, fileBlob);
        }
        else if (status == -1)
        {
            fileBlob.uploaded = false;
            fileBlob.message += "[ERROR] " + Mensajes.msgLoadCsvError;
            throw new Exception(fileBlob.message); // <------- If I remove this line, it continues processing, but it no longer changes the file, it stays with the same name or empty.

        }

        if (fileBlob.warnings.Equals(""))
        {
            fileBlob.message += Mensajes.msgLoadCsvOk;
        }
    }

    catch (Exception ex)
    {
        Console.WriteLine(ex.ToString());
        return StatusCode(500, fileBlob);
    }
    finally
    {
        Mensajes.resetMsg();
    }

    return Json(fileBlob);
}

Hello Telerik,

I am using the Kendo Upload Control with Async AutoUpload set to "true".  In version 2023.3.1114, when using "Select File" to upload a document the control works perfectly.  Dragging and dropping a file onto the control also works perfectly. 

After upgrading to 2024.1.130 using "Select File" to upload a document does not work, but dragging and dropping a file does work to upload a document.

Can you please advise me as to what I am doing wrong.  I am using jQuery v3.7.0.

@(Html.Kendo().Upload()
		.Name("uplCtrl")
		.HtmlAttributes(new { aria_label = "files", title = "Select file to upload" })
		.Multiple(false)
		.Messages(m => m.Select("Select file...")
		.DropFilesHere("Drop file here to upload"))
		.ShowFileList(false)
		.Async(a => a
			.Save("UploadSave", "Vendors")
			.AutoUpload(true)                                        
		)
		.Validation(validation =>
		{
			validation.AllowedExtensions(new string[] { "pdf", "docx", "xlsx", "zip" });
			validation.MaxFileSize(52428800);
		})
		.Events(e => e
			.Error("onUploadError")
			.Complete("onUploadSuccess")
			.Upload("onUpload")
		)
	)

Razor code-behind method: I made the razor method as simple as possible, just to see if we could get in there / or hit onpostUploadFile
        public async Task<ActionResult> OnPostUploadFile(IEnumerable<IFormFile> files, string metaData)
        {
            AllowedExtensions = new string[] { "fpd", "pdf" };

            return Page();
        }

Razor page :

@addTagHelper *, Kendo.Mvc
<div>
    <div class="demo-section">
        <kendo-upload name="files">
            <async auto-upload="true" save-url="@Url.Action("Upload","UploadFile")" chunk-size="11000" />
            <validation max-file-size="20000000" />
        </kendo-upload>
    </div>
</div>

The issue is i am not able to hit the hander from the razor page when i pass the url to <async save-url="">, Despite many efforts, the handler specified in the save-url attribute doesn't seem to be hit and returns 404.

Not Working: 

1. save-url: "/Upload/UploadFile",

2. save-url="./Upload?handler=UploadFile"

I also found Forum where it discussed the same problem but that didn't help us :https://www.telerik.com/forums/upload-using-tag-helpers

Hello!

I am trying to add a <kendo-upload> tag onto the toolbar of a kendo grid using TagHelper and ASP.NET Core

Though I am struggling with figuring out how to do this,  I have followed this template: https://demos.telerik.com/aspnet-core/grid/toolbar-template to not much success. 

My goal is to simply add a file upload option to upload an excel file to populate the fields of a grid!

Any ideas on how to progress?

Thank you!

But I am still struggling

Hello,

where can I find the controller code for ASP.NET Core Upload Asynchronous Upload. Somehow when I trying to upload my file, I keep getting an error "failed to upload the file". below is what i have in my controller:

  public ActionResult Async_Save(IEnumerable<IFormFile> files)
        {
            // The Name of the Upload component is "files"
            string path = Path.Combine(_webHostEnvironment.WebRootPath, "FileSavePath");
            string DestinationPath = _configuration["DestinationPath"].ToString();
            if (files != null)
            {
                MoveFiles mf = new MoveFiles(); 
               
                foreach (var formFile in files)
                {
                    
                  

                    using (var stream = System.IO.File.Create(DestinationPath))
                    {
                        formFile.CopyTo(stream);
                    }

                    
                }
            }

This is my cshtml code:

@using Kendo.Mvc.UI
<div style="margin-top:60px">
        <div class="block-section">
        @(Html.Kendo().Upload()
            .Name("files")
            .Async(a => a
                .Save("Async_Save", "Upload")
                .Remove("Async_Remove", "Upload")
                .AutoUpload(true)
            )
        )
    </div>
</div>