How to set up a Web API controller for multipart/form-data

This is what solved my problem
Add the following line to WebApiConfig.cs

config.Formatters.XmlFormatter.SupportedMediaTypes.Add(new System.Net.Http.Headers.MediaTypeHeaderValue("multipart/form-data"));

You can use something like this

[HttpPost]
public async Task<HttpResponseMessage> AddFile()
{
    if (!Request.Content.IsMimeMultipartContent())
    {
        this.Request.CreateResponse(HttpStatusCode.UnsupportedMediaType);
    }

    string root = HttpContext.Current.Server.MapPath("~/temp/uploads");
    var provider = new MultipartFormDataStreamProvider(root);
    var result = await Request.Content.ReadAsMultipartAsync(provider);

    foreach (var key in provider.FormData.AllKeys)
    {
        foreach (var val in provider.FormData.GetValues(key))
        {
            if (key == "companyName")
            {
                var companyName = val;
            }
        }
    }

    // On upload, files are given a generic name like "BodyPart_26d6abe1-3ae1-416a-9429-b35f15e6e5d5"
    // so this is how you can get the original file name
    var originalFileName = GetDeserializedFileName(result.FileData.First());

    var uploadedFileInfo = new FileInfo(result.FileData.First().LocalFileName);
    string path = result.FileData.First().LocalFileName;

    //Do whatever you want to do with your file here

    return this.Request.CreateResponse(HttpStatusCode.OK, originalFileName );
}

private string GetDeserializedFileName(MultipartFileData fileData)
{
    var fileName = GetFileName(fileData);
    return JsonConvert.DeserializeObject(fileName).ToString();
}

public string GetFileName(MultipartFileData fileData)
{
    return fileData.Headers.ContentDisposition.FileName;
}

5 years later on and .NET Core 3.1 allows you to do specify the media type like this:

[HttpPost]
[Consumes("multipart/form-data")]
public IActionResult UploadLogo()
{
    return Ok();
}

Perhaps it is late for the party. But there is an alternative solution for this is to use ApiMultipartFormFormatter plugin.

This plugin helps you to receive the multipart/formdata content as ASP.NET Core does.

In the github page, demo is already provided.

Here's another answer for the ASP.Net Core solution to this problem...

On the Angular side, I took this code example...

https://stackblitz.com/edit/angular-drag-n-drop-directive

... and modified it to call an HTTP Post endpoint:

  prepareFilesList(files: Array<any>) {

    const formData = new FormData();
    for (var i = 0; i < files.length; i++) { 
      formData.append("file[]", files[i]);
    }

    let URL = "https://localhost:44353/api/Users";
    this.http.post(URL, formData).subscribe(
      data => { console.log(data); },
      error => { console.log(error); }
    );

With this in place, here's the code I needed in the ASP.Net Core WebAPI controller:

[HttpPost]
public ActionResult Post()
{
  try
  {
    var files = Request.Form.Files;

    foreach (IFormFile file in files)
    {
        if (file.Length == 0)
            continue;
        
        string tempFilename = Path.Combine(Path.GetTempPath(), file.FileName);
        System.Diagnostics.Trace.WriteLine($"Saved file to: {tempFilename}");

        using (var fileStream = new FileStream(tempFilename, FileMode.Create))
        {
            file.CopyTo(fileStream);
        }
    }
    return new OkObjectResult("Yes");
  }
  catch (Exception ex)
  {
    return new BadRequestObjectResult(ex.Message);
  }
}

Shockingly simple, but I had to piece together examples from several (almost-correct) sources to get this to work properly.

For Asp.net MVC I need to validate and process before saving the file so I solve my problem by some more steps to give the file to a property. At first

HttpContext.Current.Request.Files[i]

is HttpPostedFile so I made a property with this type (I have multiple files and need more properties) so I assign file to property like below

if (HttpContext.Current.Request.Files.Count>0)
        {

            var files = HttpContext.Current.Request.Files;
            for (int i = 0; i < files.Keys.Count; i++)
            {
                if (files.Keys[i].ToLower() == "ShenasnameImage".ToLower())
                {
                    model.ShenasnameImage = files[i];
                    
                }
                if (files.Keys[i].ToLower() == "MelliCardImage".ToLower())
                {
                    model.MelliCardImage = files[i];
                    
                }
            }
        }

then I make validation and process for file properties and finally save files.

For me worked this way, hope it helps!

        [HttpPost("AddProduct")]

        public async Task<IActionResult> AddProduct( IFormFile files)
        {
            string fileGuid = Guid.NewGuid().ToString();
            var pathImage = Path.Combine(_hostEnvironment.ContentRootPath, "Images", fileGuid);
            var streamImage = new FileStream(pathImage, FileMode.Append);
            await files.CopyToAsync(streamImage);

            return Ok();

           
        }

check ur WebApiConfig and add this

GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();