控制器
public ActionResult EditProduct(int id)
{
ProductViewModel ViewModel = new ProductViewModel();
ViewModel.SingleProduct = DB.Prouducts.Where(x => x.ProductID == id).FirstOrDefault();
ViewModel.ImageList = DB.ImageGalleries.Where(x => x.ProductIdFk == id).ToList();
return View(ViewModel);
}
[HttpPost]
public ActionResult EditProduct(Prouduct product, IEnumerable<HttpPostedFileBase> thumb, ImageGallery images)
{
CategoryDropdown();
BrandDropdown();
if (ModelState.IsValid)
{
HttpPostedFileBase Image1 = thumb.FirstOrDefault();
product.ProductSlug = slug;
var userID = Convert.ToInt32(Session["UserID"]);
product.UserIdFk = userID;
DB.Entry(product).State = System.Data.Entity.EntityState.Modified;
DB.SaveChanges();
int LastInsertedID = product.ProductID;
foreach (var tmb in thumb)
{
if (tmb != null)
{
string FileName = tmb.FileName;
string Extenstion = Path.GetExtension(FileName);
if (Extenstion.ToLower() == ".jpeg" | Extenstion.ToLower() == ".jpg" | Extenstion.ToLower() == ".png" | Extenstion.ToLower() == ".webp")
{
FileName = FileName + DateTime.Now.ToString("yyyyMMddHHmmssfff") + Extenstion;
string ImageSavePath = Server.MapPath("/Content/Assets/Photos/");
tmb.SaveAs(Path.Combine(ImageSavePath + FileName));
string ThumbSavePath = Server.MapPath("/Content/Assets/Photos/Thumbs/");
ThumbGenration.ResizeStream(522, tmb.InputStream, Path.Combine(ThumbSavePath + FileName));
images.ImageName = FileName;
images.ImageThumb = FileName;
images.ProductIdFk = LastInsertedID;
//var userID = Convert.ToInt32(Session["UserID"]);
images.UserIdFk = userID;
DB.ImageGalleries.Add(images);
DB.SaveChanges();
TempData["Success"] = "Data Added Successfully!";
}
}
}
}
return View();
}
查看
@model RentalServices.Models.ProductViewModel
@using (Html.BeginForm("EditProduct", "Product", FormMethod.Post, new { enctype = "multipart/form-data" }))
{
@Html.AntiForgeryToken()
@Html.ValidationSummary(true, "", new { @class = "text-danger" })
@Html.HiddenFor(model => model.SingleProduct.ProductID);
<div class="add-item-wrapper">
<h4>Listing Details</h4>
<hr class="noPadMar" />
<div class="add-item">
<div class="row">
<div class="col-sm-10 col-sm-offset-1">
<div class="col-md-12 col-sm-12 form-group">
@*<label class="col-sm-3 col-md-3 control-label">Title</label>*@
@Html.LabelFor(model => model.SingleProduct.Title, htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@*<input type="text" class="form-control" placeholder="TITLE" />*@
@Html.EditorFor(model => model.SingleProduct.Title, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.SingleProduct.Title, "", new { @class = "text-danger" })
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.LabelFor(model => model.SingleProduct.Price, htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.EditorFor(model => model.SingleProduct.Price, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.SingleProduct.Price, "", new { @class = "text-danger" })
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.Label("CATEGORY", htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.DropDownListFor(model => model.SingleProduct.CategoryIdFk, ViewBag.CategoryDropdown as SelectList, "CHOOSE CATEGORY", new { @class = "form-control", id = "CategoryID" })
@Html.ValidationMessageFor(model => model.SingleProduct.CategoryIdFk, "", new { @class = "text-danger" })
</div>
</div>
<div id="hide">
<div class="col-md-12 col-sm-12 form-group">
@Html.Label("BRAND", htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.DropDownListFor(model => model.SingleProduct.BrandIdFk, ViewBag.BrandDropdown as SelectList, "CHOOSE BRAND", new { @class = "form-control", id = "BrandID" })
@Html.ValidationMessageFor(model => model.SingleProduct.BrandIdFk, "", new { @class = "text-danger" })
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.LabelFor(model => model.SingleProduct.Ram, htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.EditorFor(model => model.SingleProduct.Ram, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.SingleProduct.Ram, "", new { @class = "text-danger" })
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.LabelFor(model => model.SingleProduct.Processor, htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.EditorFor(model => model.SingleProduct.Processor, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.SingleProduct.Processor, "", new { @class = "text-danger" })
</div>
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.Label("CONDITION", htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.DropDownListFor(model => model.SingleProduct.Conditon, selectList, "CHOOSE CONDITION", new { @class = "form-control" })
@Html.ValidationMessageFor(model => model.SingleProduct.Conditon, "", new { @class = "text-danger" })
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.LabelFor(model => model.SingleProduct.Location, htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.EditorFor(model => model.SingleProduct.Location, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.SingleProduct.Location, "", new { @class = "text-danger" })
</div>
</div>
<div class="col-md-12 col-sm-12 form-group">
@Html.LabelFor(model => model.SingleProduct.Description, htmlAttributes: new { @class = "col-sm-3 col-md-3 control-label" })
<div class="col-sm-9">
@Html.TextAreaFor(model => model.SingleProduct.Description, new { htmlAttributes = new { @class = "form-control" } })
@Html.ValidationMessageFor(model => model.SingleProduct.Description, "", new { @class = "text-danger" })
</div>
</div>
</div>
</div>
</div>
</div>
<div class="image-gallery-wrapper">
<div class="img-gallery">
@if (Model.ImageList.Any())
{
foreach (var item in Model.ImageList)
{
<div class="img-wrapper">
<p>Image 1</p>
<div class="img-box">
<input type="file" name="thumb" value="" class="file-style" onchange="readURL(this)" ; />
<img src="/Content/Assets/Photos/Thumbs/@item.ImageName" alt="your image" id="imgName" value="@item.ImageName" />
<button id="RemoveImage">Remove Image</button>
</div>
</div>
}
}
</div>
</div>
<div class="text-center">
<button type="submit" class="roundSubmitBtn" style="background:#7048f0 !important;font-size:14px !important; margin-top:40px;">SUMBIT <i class="fa fa-arrow-right"></i></button>
</div>
}
当我添加我的代码时，我得到了null异常error。但是我是否检查了null，所以为什么我得到了这个null对象引用错误。 而且我还尝试了IF语句中的Count（）和！= null。我在提交表单时遇到错误，并且错误为null异常错误，所以请告诉我我错了
答案 0 :(得分：1)
通过检查提供的POST动作方法，问题似乎出自return View()语句，该语句返回与GET动作方法相同的视图页面，但未返回viewmodel类实例，这导致ProductViewModel.ImageList包含空值。
下面的简短代码显示了问题：
[HttpPost]
public ActionResult EditProduct(Prouduct product, IEnumerable<HttpPostedFileBase> thumb, ImageGallery images)
{
CategoryDropdown();
BrandDropdown();
if (ModelState.IsValid)
{
// image processing and saving to DB
}
// the view returned without viewmodel
// this will trigger NullReferenceException because ProductViewModel.ImageList is not reassigned yet
return View();
}
因此，在将发布的数据保存到数据库之后，应重新分配ProductViewModel.ImageList属性，并与新的ProductViewModel实例一起返回相同的视图（或在必要时通过遵循{{ 1}}）：
RedirectToAction