为什么 Controller 'Get' Edit 方法在 ASP.NET Core 6 MVC 中被调用两次？

Question

我在编辑视图中遇到问题。 当我调试我的代码时，在Id从ShowCategory视图传递到 controller 中的EditPostGroup方法后，它工作正常，但在页面加载后， Id零被发送到 controller 中的 Edit 方法并抛出错误

Object 引用未设置为 object 的实例

这是我的代码：此方法在PostRepository中并从数据库中获取带有Id的postGroup ：

    public PostGroupViewModel GetPostGroupById(int postGroupId)
    {
        var postGroup = _context.PostGroups.Find(postGroupId);

        PostGroupViewModel postGroupViewModel = new PostGroupViewModel()
        {
             GroupId = postGroup.GroupId,
             GroupTitle = postGroup.GroupTitle,
             GroupImageName = postGroup.GroupImageName,
             IsDelete =  postGroup.IsDelete,
             ParentId = postGroup.ParentId
        };

        return postGroupViewModel;
    }

这些是CategoryController中的Get和Post编辑方法：

    [HttpGet]
    public IActionResult EditPostGroup(int id)
    {
        var groups = _postService.GetGroupForManagePost();
        ViewData["Groups"] = new SelectList(groups, "Value", "Text");
        var postGroupViewModel = _postService.GetPostGroupById(id);
        return View(postGroupViewModel);
    }

    [HttpPost]
    public IActionResult EditPostGroup(PostGroup postGroup, IFormFile imgPostGroupUp)
    {
        if (!ModelState.IsValid)
            return View("EditPostGroup");

        _postService.UpdatePostGroup(postGroup, imgPostGroupUp);

        return RedirectToAction("ShowCategory", "Category");
    }

这是“ShowCategory”视图，它将 PostGroupId 发送到 Edit 操作方法：

    @{
        ViewData["Title"] = "Category List";
       
    }
    
    <div class="row">
        <div class="col-lg-12">
            <h4 style="color:darkblue;" >Category List</h4>
        </div>
        <!-- /.col-lg-12 -->
    </div>
    <br />
    <div class="row">
        <div class="col-lg-12">
            <div class="panel panel-default">
            
                <div class="panel-body">
                    <br />
                
                    <div class="col-md-12" style="margin: 10px 0;">   
                        <a asp-controller="Category" asp-action="CreateCategory" asp-area="Admin" class="btn btn-outline btn-success">Create Category</a>               
                    </div>
                    <br />
                    <br />
                    <br />
                    <table class="table table-striped table-bordered table-hover dataTable no-footer text-center" id="dataTables-example" aria-describedby="dataTables-example_info">
                        <thead class="table-success black-ribon">
                            <tr>
                              
                                <th>Title</th>
                                <th>Parent Category</th>
                                <th>Image</th>
                                <th>Operations</th>
                            </tr>
                        </thead>
                        <tbody>
                        @foreach (var item in  @ViewBag.CategoryList)
                        {
                            <tr>
                          
                                <td>
                                    @item.GroupTitle
                                </td>
                                <td>
                                    @item.ParentId
                                </td>
                                <td>
                                    <img class="thumbnail" style="width:40px;height:40px;"  src="/img/postGroup/@item.GroupTitle/@item.GroupImageName" alt="">
                                </td>
    
                                <td>
                                    <a href="/Admin/Category/EditPostGroup/@item.GroupId" class="btn btn-primary btn-md">
                                        Edit
                                    </a>
                                </td>
                            </tr>
                        }
                        </tbody>
                    </table>
    
                </div>
                <!-- /.panel-body -->
            </div>
            <!-- /.panel -->
        </div>
        <!-- /.col-lg-12 -->
    </div>

这是EditPostGroupView ：

    @model DataLayer.Models.ViewModels.PostGroup.PostGroupViewModel
    @{
        ViewData["Title"] = "Post Edit";
        //Layout = "~/Areas/Admin/Views/Shared/_AdminLayout.cshtml";
    }
    
    <div class="row">
        <form method="post" asp-action="EditPostGroup" enctype="multipart/form-data">
            @* <input type="hidden" asp-for="GroupId" />*@
            @*<input type="hidden" asp-for="Post.PostImageName"/>*@
      
            <div class="col-md-8">
                <h2>Category List</h2>
                <hr/>
                <div class="form-group">
                    <label>Title</label>
                    <input type="text" asp-for="GroupTitle" class="form-control">
                    <span asp-validation-for="GroupTitle"></span>
                </div>
                <div class="form-group">
                    <label>ParentId</label>
                    <select class="form-control" asp-for="ParentId" asp-items="@(ViewData["Groups"] as SelectList)">
                    <option value="">-- please select --</option>
                    </select>
                    <span asp-validation-for="ParentId"></span>
                </div>
            </div>
            <div class="col-md-4">
                <p></p>
                <img id="imgPost" class="thumbnail" src="img/postGroup/@Model.GroupTitle/@Model.GroupImageName"/>
                <div class="form-group">
                    <label>Select Image</label>
                    <input type="file" name="imgPostGroupUp" id="imgPostGroupUp">
                </div> 
            </div> 
            <input type="submit" value="Edit" class="btn btn-success"/>
        </form>
    </div>
        
    @section scripts
        {
        <script>    
            function readURL(input) {   
                if (input.files && input.files[0]) {
                    var reader = new FileReader();
    
                    reader.onload = function (e) {
                        $('#imgPost').attr('src', e.target.result);
                    }
    
                    reader.readAsDataURL(input.files[0]);
                }
            }
    
            $("#imgPostUp").change(function () {
                readURL(this);
            });
        </script>         
    }

这是 Program.cs 中的路由：

app.MapControllerRoute(
    name: "MyArea",
    pattern: "{area:exists}/{controller=Home}/{action=Index}/{id?}");

app.MapControllerRoute(
    name: "default",
    pattern: "{controller=Home}/{action=Index}/{id?}");

这是邮政组 Model：

public class PostGroup
    {
        [Key]
        public int GroupId { get; set; }
        //public int? SubGroupId { get; set; }

        public string GroupTitle { get; set; }

        [MaxLength(50)]
        public string? GroupImageName { get; set; }

        public bool IsDelete { get; set; }

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

        [ForeignKey("ParentId")]
        public  List<PostGroup>? PostGroups { get; set; }

        [InverseProperty("PostGroup")]
        //[NotMapped]
        public  List<Post>? Posts { get; set; }
}

这是 postGroupViewModel：

public class PostGroupViewModel
    {
        public int GroupId { get; set; }
  
        public string GroupTitle { get; set; }

        [MaxLength(50)]
        public string? GroupImageName { get; set; }

        public bool IsDelete { get; set; }

        public int? ParentId { get; set; }
    }

问题是什么？

Program.cs和中间件有问题吗？

我将EditPostGroup(PostGroup postGroup, IFormFile imgPostGroupUp)方法更改为EditPostGroup(PostGroupViewModel postGroupViewModel, IFormFile imgPostGroupUp) ，但仍然存在问题。

Answer 1

您可以使用查询字符串而不是在 .net 核心中传递 id：

[HttpGet]
    public async Task<IActionResult> Edit()
    {
        string id = HttpContext.Request.Query["id"].ToString();
        var model = await _service.FindAsync(int.Parse(id));
        return View(model);
    }

在 razor 查看：

<a href="/service/edit?id=@item.ServiceId">

此外，在 razor 视图中的文件的 src 中使用 # 会导致此问题。 删除它或给它一个值。

<img id="img-master" class="thumbnail" src="#" />

到

<img id="img-master" class="thumbnail" src="/images/@Model.ImageEdit" />