In this article I will explain with an example, how to solve the problem i.e. IFormFile always returns NULL when used in Controller while uploading files in ASP.Net Core MVC.
There are two reasons. First the name of the IFormFile parameter and the name of HTML FileUpload element must be exact same and second that the Form element must be specified with the enctype attribute.
Note: For beginners in ASP.Net MVC Core, please refer my article ASP.Net MVC Core Hello World Tutorial with Sample Program example.
 
 
Controller
The Action method Index by default supports the GET operation and hence another overridden method for POST operation is created which accepts the parameter which is a collection of type IFormFile.
Note: The name of the IFormFile parameter and the name of HTML FileUpload element must be exact same, otherwise the IFormFile parameter will be NULL.
 
First a check is performed whether Directory (Folder) exists if not then the Directory (Folder) is created inside the www Folder using IHostingEnvironment interface and then a loop is executed and one by one each file is saved to the Directory (Folder).
Note: For more details about IHostingEnvironment interface, please refer Using IHostingEnvironment in ASP.Net Core.
 
Finally a message is displayed to the user using ViewBag.
Note: For more details on displaying message using ViewBag, please refer my article Display (Pass) String Message from Controller to View in ASP.Net MVC.
 
public class HomeController : Controller
{
    private IHostingEnvironment Environment;
 
    public HomeController(IHostingEnvironment _environment)
    {
        Environment = _environment;
    }
 
    public IActionResult Index()
    {
        return View();
    }
 
    [HttpPost]
    public IActionResult Index(List<IFormFile> postedFiles)
    {
        string wwwPath = this.Environment.WebRootPath;
        string contentPath = this.Environment.ContentRootPath;
 
        string path = Path.Combine(this.Environment.WebRootPath, "Uploads");
        if (!Directory.Exists(path))
        {
            Directory.CreateDirectory(path);
        }
 
        List<string> uploadedFiles = new List<string>();
        foreach (IFormFile postedFile in postedFiles)
        {
            string fileName = Path.GetFileName(postedFile.FileName);
            using (FileStream stream = new FileStream(Path.Combine(path, fileName), FileMode.Create))
            {
                postedFile.CopyTo(stream);
                uploadedFiles.Add(fileName);
                ViewBag.Message += string.Format("<b>{0}</b> uploaded.<br />", fileName);
            }
        }
 
        return View();
    }
}
 
 
View
The View consists of an HTML Form which has been created using the Razor Tag attributes with the following attributes.
asp-action – Name of the Action. In this case the name is Index.
asp-controller – Name of the Controller. In this case the name is Home.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
Note: The Form element must be specified with enctype attribute and its value must be multipart/form-data, otherwise the IFormFile parameter will be NULL.
 
There is an HTML FileUpload element, a Submit Button and a SPAN element for displaying Message enclosed in a Form element.
The HTML FileUpload element has been specified with an additional HTML5 attribute multiple = “multiple” in order to allow user to select multiple files.
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width"/>
    <title>Index</title>
</head>
<body>
    <form method="post" enctype="multipart/form-data" asp-controller="Home" asp-action="Index">
        <span>Select File:</span>
        <input type="file" name="postedFiles" multiple/>
        <input type="submit" value="Upload"/>
        <br/>
        <span style="color:green">@Html.Raw(ViewBag.Message)</span>
    </form>
</body>
</html>
 
 
Screenshot
ASP.Net Core: IFormFile always returns NULL
 
 
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