用mvc表格上传

Question

I have a simple question. Why in code below, this part - HttpPostedFileBase file - is null? Of course ArticleModel model is not null, just file .

Begin of my controler action:

public ActionResult Add(ArticleModel model, HttpPostedFileBase file)
...

My form:

<section id="">
@using (Html.BeginForm()) {
    @Html.AntiForgeryToken()
    @Html.ValidationSummary()
    @ViewBag.Status


    <fieldset>
        <legend>Add</legend>
        <ol>
            <li>
                @Html.LabelFor(m => m.title)
                @Html.TextBoxFor(m => m.title)
            </li>
            <li>
                @Html.LabelFor(m => m.Categories)
                @Html.DropDownListFor(m=> m.categoryID, Model.Categories, "- lorem -", new { @class="dropdownlist" })
            </li>
            <li>
                @Html.LabelFor(m => m.connectedArticlesID)
                @Html.TextBoxFor(m => m.connectedArticlesID)
            </li>
            <li>
                 <input type="file" name="file" id="file" />
            </li>
            <li>
                @Html.LabelFor(m => m.introduction)
                @Html.EditorFor(m => m.introduction)
            </li>
            <li>
                @Html.LabelFor(m => m.content)
                @Html.EditorFor(m => m.content)
            </li>
        </ol>
        <input type="submit" value="Add" />
    </fieldset>
}
</section>

EDIT:

my model

public class ArticleModel
{
    [Display(Name = "Number")]
    public int articleID { get; set; }

    [Required]
    [Display(Name = "Tilte")]
    [StringLength(250, ErrorMessage = "Tytuł musi mieć długość od {0} do {2} znaków.", MinimumLength = 6)]
    public string title { get; set; }

    [Required]
    [Display(Name = "Similar articles")]
    public string connectedArticlesID { get; set; }

    [Display(Name = "CategoryName")]
    public string category { get; set; }

    [Required]
    [Display(Name = "Category")]
    public int categoryID { get; set; }

    [Required]
    [Display(Name = "Category")]
    public IEnumerable<SelectListItem> Categories
    {
        get
        {
            return new[]
            {
                new SelectListItem { Value = "1", Text = "Kategoria pierwsza" },
                new SelectListItem { Value = "2", Text = "Kategoria druga" },
                new SelectListItem { Value = "3", Text = "Kategoria trzecia" },
            };
        }
    }

    [Display(Name = "Content")]
    [Required]
    [StringLength(6000, ErrorMessage = "Treść musi mieć długość od {1} do {2} znaków.", MinimumLength = 30)]
    [UIHint("tinymce_jquery_full"), AllowHtml]
    public string content { get; set; }

    [Display(Name = "Introduction")]
    [Required]
    [StringLength(6000, ErrorMessage = "Wstęp musi mieć długość od {1} do {2} znaków.", MinimumLength = 30)]
    [DataType(DataType.MultilineText)]
    public string introduction { get; set; }
}

Answer 1

I have a simple question. Why in code below, this part - HttpPostedFileBase file - is null?

Because you didn't set the enctype to multipart/form-data on your form:

@using (Html.BeginForm(null, null, FormMethod.Post, new { enctype = "multipart/form-data" })) 
{
    ...
}

Reference: http://haacked.com/archive/2010/07/16/uploading-files-with-aspnetmvc.aspx

And before you switch your Html.BeginForm to an Ajax.BeginForm and then ask a question why HttpPostedFileBase file - is null , the answer is you cannot upload files using AJAX. You will have to use a file upload plugin such as Uploadify or Blueimp File upload. I am just mentioning this for the record in order to avoid further possible duplicate questions.

---

UPDATE:

As requested in the comments section you could add the file field to your view model:

public class ArticleModel
{
    [Required]
    public HttpPostedFileBase File { get; set; }

    ...
}

and then have your controller action directly take this view model as argument and get rid of the HttpPostedFileBase argument:

public ActionResult Add(ArticleModel model)
{
    if (ModelState.IsValid)
    {
        ... work with model.File directly here
    }
}

Also to avoid any ambiguity between your domain models and view models, I would suffix them with ViewModel:

public class ArticleViewModel
{
    ...
}