ASP.NET Core MVC 中下拉筛选器的 InvalidOperationException

问题描述 投票：0回答：1

我在导航栏上创建了一个全局下拉过滤器。我收到错误：

处理请求时发生未处理的异常。

InvalidOperationException：传递到 ViewDataDictionary 的模型项的类型为“System.String”，但此 ViewDataDictionary 实例需要类型为“Website.ViewModels.CardsViewModel.CardsViewModel”的模型项。

Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary.EnsureCompatible（对象值）

这是我的代码-

FilterController.cs
：

  • 当我打开网站中的帖子页面时，
    FilterController.cs
    中的_cache.Set()将代码重定向到PostController.cs。只有这样我的代码才会出错。
public IActionResult Index(string postCategory)
{
    var categoryLst = new List<string>();

    var categoryQry = from p in _context.Posts
                      orderby p.PostCategory 
                      select p.PostCategory;

    categoryLst.AddRange(categoryQry.Distinct());
    ViewBag.movieGenre = new SelectList(categoryLst);

    var posts = from c in _context.Posts
                select c;

    if (!string.IsNullOrEmpty(postCategory))
    {
        posts = posts.Where(x => x.PostCategory == postCategory);
    }

    _cache.Set("category", postCategory);
    ViewBag.PostCategory = postCategory;

    string url = Request.Headers["Referer"].ToString();

    return Redirect(url);
}


PostController.cs
：

  • FilterController.cs
    中的_cache.Set()将代码重定向到此处。
  • 我编辑了下面的代码。
[HttpGet]
public async Task<IActionResult> Index()
{
    var CardPostVM = new CardsViewModel
    {
        PostCard = await _context.Posts.ToListAsync()
    };

    var cached = _cache.TryGetValue("category", out var postCategory);

    if (cached)
    {
        return View(postCategory);
    }

    return View(CardPostVM);
}

（参考文件）：

使用 _PartialLayout 

_TopNavbar.cshtml
作为我的导航栏。这是下拉过滤器的视图：

<!-- dropdown filter -->
<form class="ps-lg-5" asp-controller="Filter" asp-action="Index" id="category" method="get">
    <div class="input-group ps-lg-5">
        <select class="form-control shadow-none" name="postCategory" id="post-filter">
            <option>All</option>">
            @foreach (var item in cardsVM.PostCategories)
            {
                <!option value="@item.CategoryName"  @(item.CategoryName.ToString() == ViewBag.PostCategory?.ToString() ? "selected" : "")>@item.CategoryName</!option>
            }
        </select>
        <button class="btn btn-outline-success shadow-none me-2" type="submit"><i class='bx bx-filter'></i></button>
    </div>
</form>


CardsViewModel.cs
（错误中提到）：

public class CardsViewModel
{
    public List<PostModel>? PostCard { get; set; }
}

更新（参考文件）：

_Layout.cshtml
是提到
_TopNavbar.cshtml
的地方。

<!DOCTYPE html>
<html lang="en">
<head>
    <!--Links-->
</head>

<body id="body-pd">

    <!--Top Nav bar-->
    <div>
        <partial name="~/Views/Shared/TopNavbar/_TopNavbar.cshtml" />
    </div>

    <!--Render Body-->
    <div class="container">
        <main role="main" class="pb-3">
            @RenderBody()
        </main>
    </div>

    <!--Links-->

    @await RenderSectionAsync("Scripts", required: false)

</body>
</html>

这是一个 _PartialLayout 文件 

_PostCards.cshtml
，其中包括 @model CardsViewModel:

@using RecipeWebsite.ViewModels.CardsViewModel

@model CardsViewModel

@foreach (var item in Model.PostCard)
{
    // Detail of Card where my data is displayed
    <div class="col mb-4">
        <div class="card shadow-sm">
            <img class="bd-placeholder-img card-img-top" src="@item.Image" width="157" height="236" alt="Card image cap">

            <!--Card Details-->
            <div class="card-body">
                <a asp-controller="Post" asp-action="Detail" asp-route-id="@item.Id" class="stretched-link"></a>
                <h6 class="card-text"> @item.Title </h6>
                <div class="d-flex justify-content-between align-items-center mb-2">
                    <p class="small text-secondary">@item.PostCategory</p>
                </div>            
            </div>        
        </div>
    </div> 
}

提及

PostCards.cshtml
的文件

@using RecipeWebsite.ViewModels.CardsViewModel

@model CardsViewModel

<main>

    <!-- Cards -->
    @if (Model.PostCard.Count != 0)
    {
        <div class="album py-5 bg-light">
            <div class="container">

                <div class="row row-cols-1 row-cols-sm-2 row-cols-md-3 g-3">

                    <partial name="~/Views/Shared/Cards/_PostCards.cshtml" />

                </div>

            </div>
        </div>
    }
    else 
    {
        // Error
    }

</main>

谢谢你

c# filter asp.net-core-mvc unhandled-exception invalidoperationexception
1个回答
0
投票

这是我的回答

  • 需要更改 
    FilterController.cs
    和 
    PostController.cs

FilterController.cs
：

public async Task<IActionResult> Index(string postCategory)
{
    var filteredPost = from p in _context.Posts select p;

    if (!string.IsNullOrEmpty(postCategory))
    {
        ViewBag.PostCategory = postCategory;

        filteredPost = filteredPost.Where(p => p.PostCategory == postCategory);
    }

    var filteredCategory = new CardsViewModel
    {
        PostCard = await filteredPost.ToListAsync()
    };

    _cache.Set("filteredCategory", filteredCategory);

    string url = Request.Headers["Referer"].ToString();

    return Redirect(url);
}

PostController.cs

[HttpGet]
public async Task<IActionResult> Index()
{
    var CardPostVM = new CardsViewModel
    {
        PostCard = await _context.Posts.ToListAsync()
    };

    var cached = _cache.TryGetValue("filteredCategory", out var filteredCategory);
    if (cached)
    {
        return View(filteredCategory);
    }

    return View(CardPostVM);
}
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