@foreach（模型中的变量项）是 NullReferenceException

Question

我正在使用 ASP.NET 核心 MVC。我尝试在提交表单并获得回复时显示文本。

我确实设法将数据更新到数据库，但我想在浏览器上显示它们。

当我尝试这样做时，我遇到了 NullReferenceException 错误，即使我在数据库中有数据

这是我的代码 - 控制器：

 public ActionResult CommentIndex()
    {
        return View();
    }

    [HttpPost]
    public ActionResult _CommentIndex(Comment comment, int id)
    {
        ModelState.Clear();
        _context.Add(comment);
        _context.Comments.Add(comment);
        _context.SaveChanges();

        List<Comment> commentList = _context.Comments.ToList();

        return PartialView(commentList);
    }

我的部分看法：

@model IEnumerable<PetShop.Data.Models.Comment>

  <div class="panel panel-primary">
        <div class="panel-heading">
           
        </div>
        <div class="panel-body">
            @if (Model != null || Model.Count() < 1)
            {
                using (Html.BeginForm("CommentIndex", "Category", FormMethod.Post))
                {
                    foreach (var item in Model)
                    {
                        <p>@item.Content</p>
                      
                    }
                }
            }
            else
            {
               <p>No results found</p>
            }
        </div>
    </div>

我的看法：

<div class="row">
    <div class="form-group">
        <div class="col-md-6">
            <form id="commentPartial">
                <label>Enter your comment</label>
                <input type="text" id="Content" name="Content" placeholder="Enter your comment" />
                <button type="submit" class="btn btn-primary">Post Comment</button>
            </form>
        </div>
    </div>
</div>
<div class="row">
    <div id="commentDisplay"></div>
</div>

ajax 在视图中：

    @section scripts {
<script>
    $(document).ready(function () {
        $('#commentPartial').submit(function () {
            $.ajax({
                method: "POST",
                url: "/Category/CommentIndex",
                data: $(this).serialize(),
                success: function (result) {
                    $('#commentDisplay').html(result);
                }
            });
            return false;
        });
    });
</script>
}

我的模特：

public class Comment
{
    public Comment() => Animal = new Animal();
    [Key]
    public int CommentId { get; set; }
    public int AnimalId { get; set; }
    public string Content { get; set; }

    [ForeignKey("AnimalId")]
    public virtual Animal Animal { get; set; }
}

Answer 1

As per your expectations assuming you are looking for something like below:

Output

Controller Action For Intial Page

 public ActionResult CommentIndex()
        {
            return View();
        }

View For Display Intial Page

@{
}
<div class="row">
        <div class="form-group">
            <div class="col-md-6">
                <form id="commentPartial">
                    <label>Enter your comment</label>
                    <input type="text" id="Content" name="Content" placeholder="Enter your comment" />
                    <button type="submit" class="btn btn-primary">Post Comment</button>
                </form>
            </div>
        </div>
    </div>
    <div class="row">
        @*This is where your comment partial view will appear appear when user hits submit on our form*@
        <div id="commentDisplay"></div>
    </div>




    @section scripts {
    <script>
        $(document).ready(function () {
            //When the user hit the submit button we will post the form results to our partial view controller
            $('#commentPartial').submit(function () {
                $.ajax({
                    method: "POST",
                    url: "/Controller/_CommentIndex",
                    data: $(this).serialize(),
                    success: function (result) {
                        //When then load our partial view into our containing div on the main page
                        $('#commentDisplay').html(result);
                    }
                });
                return false;
            });
        });
    </script>
    }

Controller Action For Partial View

[HttpPost]
public ActionResult _CommentIndex([Bind("Content,AnimalId")] Comment comment, int id)
{
    
    _context.Comments.Add(comment);
    _context.SaveChanges();

    List<Comment> commentList = _context.Comments.ToList();

    return PartialView(commentList);
}

Note: Feel free to implement your logic for ModelState.IsValid or any conditional you want.

Model used in above controller

public class Comment
    {
        public int CommentId { get; set; }
        public int AnimalId { get; set; }
        public string Content { get; set; }
    }

Note: I am using on Content property for testing the scenario, feel free to modify as per your need.

Partial View

@model IEnumerable<DotNetMVCWebApp.Models.Comment>

    <div class="panel panel-primary">
            <div class="panel-heading">
               
            </div>
            <div class="panel-body">
                @if (Model != null || Model.Count() < 1)
                {
                    using (Html.BeginForm("CommentIndex", "Home", FormMethod.Post))
                    {
                        foreach (var item in Model)
                        {
                            <p>@item.Content</p>
                          
                        }
                    }
                }
                else
                {
                   <p>No results found</p>
                }
            </div>
        </div>

Note: While you would be creating this partial view remember to add Comment And add List kind of partial view.

希望它能相应地指导你

@foreach（模型中的变量项）是 NullReferenceException

@foreach(var item in Model) is NullReferenceException

c#

asp.net-core-mvc