当我尝试上传图像 ASP.NET MVC 4 时，我收到“用户代码未处理 NullReferenceException”的错误

Question

Controler

    [HttpPost]
    public ActionResult Index(Add_Book _books)
    {
        BusinessLayer booksBusinessLayer = new BusinessLayer();
        //books file = new books();
        //var book = new books();

receiving error at below line

        var fileName = Path.GetFileName(_books.File.FileName);
        //var fileName = book.File.FileName;
        var path = Path.Combine(Server.MapPath("~/Osho_Images"), fileName);
        book.File.SaveAs(path);

        booksBusinessLayer.AddBooks(_books);

        return View();
    }

Modal

public class books
{
    public string ID
    {
        get;
        set;
    }

    public string ISBN
    {
        get;
        set;
    }

    public string Book_Title
    {
        get;
        set;
    }

    public string Book_Cat
    {
        get;
        set;
    }

    public string Language
    {
        get;
        set;
    }

    public string Book_Desc
    {
        get;
        set;
    }

    public string Price
    {
        get;
        set;
    }

    public string Book_Img
    {
        get;
        set;
    }

    public HttpPostedFileBase File
    {
        get;
        set;
    }

    public int Qty
    {
        get;
        set;
    }

    public int Qty_Alert
    {
        get;
        set;
    }
 }

Pleas provide the solution.

Answer 1

Like David Tansey say, _books.File.FileName assume that is NOT null, so you need to validate before to try get access to the object,

When I worked with upload files I did something like the following code, hope this help you

just use in your view

   <input type="file" />

then in your controller, in this case i put the for, because the user can upload multiple files,

   [HttpPost]
    public ActionResult SaveFile(YourModel model)
    {
        foreach (string file in Request.Files)
        {
           SaveYourFile(Request.Files[file]);
        }
    return View();
    } 

     private void SaveYourFile(HttpPostedFileBase file)
     {
       if(file.ContentLenght >0)
         {
           //now you can access to your uploaded file
          var book = new books();
        var path = Path.Combine(Server.MapPath("~/Osho_Images"), file.fileName);
         book.File.SaveAs(path);

          booksBusinessLayer.AddBooks(_books);
         }
     }