如何在asp.net core mvc中制作级联下拉菜单？

Question

我之前曾尝试过，但未能取得成功。

谁能用例子告诉我？

Answer 1

您可以参考以下步骤在asp.net core MVC中创建级联下拉列表。

1. 创建具有关系的模型：

    public class Category
    {
        public int Id { get; set; }
   
        [Required]
        [Display(Name = "Category Name")]
        public string CategoryName { get; set; }
   
        public ICollection<SubCategory> SubCategories { get; set; }
    }
   
    public class SubCategory
    {
        public int Id { get; set; }
   
        [Required]
        [Display(Name = "SubCategory Name")]
        public string SubCategoryName { get; set; }
   
        public int CategoryID { get; set; }
   
        public Category Category { get; set; }
    }
   

2. 然后使用EF core迁移在数据库中创建相关表，或者创建一个服务来设置初始数据。这里我创建一个服务：

    public interface IRepository
    {  
        List<Category> GetCategories(); 
    }
   
    public class Repository : IRepository
    {
        private readonly ApplicationDbContext db;
        public Repository(ApplicationDbContext context)
        {
            db = context;
        }
        //you can also query the database and get the data.
   
        public List<Category> GetCategories()
        {
            List<Category> categories = new List<Category>()
            {
                new Category(){ Id=101, CategoryName="Category 1", 
                    SubCategories= new List<SubCategory>(){
                    new SubCategory(){ Id=1001, SubCategoryName="SubCategory 1.1"},
                    new SubCategory(){ Id=1002, SubCategoryName="SubCategory 1.2"},
                    new SubCategory(){ Id=1003, SubCategoryName="SubCategory 1.3"},
                    }
                },
                new Category(){ Id=102, CategoryName="Category 2",
                    SubCategories= new List<SubCategory>(){
                    new SubCategory(){ Id=1001, SubCategoryName="SubCategory 2.1"},
                    new SubCategory(){ Id=1002, SubCategoryName="SubCategory 2.2"},
                    new SubCategory(){ Id=1003, SubCategoryName="SubCategory 2.3"},
                    }
                },
                new Category(){ Id=103, CategoryName="Category 3",
                    SubCategories= new List<SubCategory>(){
                    new SubCategory(){ Id=1001, SubCategoryName="SubCategory 3.1"},
                    new SubCategory(){ Id=1002, SubCategoryName="SubCategory 3.2"},
                    new SubCategory(){ Id=1003, SubCategoryName="SubCategory 3.3"},
                    }
                },
   
            };
   
            return categories;
        }
    }
   

3. 在 Startup.ConfigureServices 方法中注册服务：

        services.AddTransient<IRepository, Repository>();
   

4. 然后，在MVC控制器中，使用以下代码来获取类别和子类别：

    public class HomeController : Controller
    { 
        private readonly ApplicationDbContext _context; //db context.
        private readonly IRepository _repository;
        public HomeController( ApplicationDbContext context, IRepository repository)
        { 
            _context = context; 
            _repository = repository;
        }
   
        public IActionResult CreateIndex() {
   
            //get the categories.
            ViewBag.CategoryId = _repository.GetCategories().Select(c => new SelectListItem { Value= c.Id.ToString(),Text = c.CategoryName }).ToList();
   
            return View();
        }
        //get Subcategory based on the category id
        public IActionResult GetSubCategory(int cid)
        {
            var SubCategory_List = _repository.GetCategories().Where(s => s.Id == cid).FirstOrDefault().SubCategories.Select(c => new { Id = c.Id, Name = c.SubCategoryName }).ToList();
            return Json(SubCategory_List);
        }
        [HttpPost]
        public IActionResult CreateIndex(ProductViewModel product)
        { 
            return View();
        }
   

5. 视图页面（CreateIndex.cshtml）中的代码，在页面加载时仅填充类别下拉列表，然后使用 JQuery 调用操作方法并填充子类别：

    @model MVCDemo.Models.ProductViewModel
   
    @{
        ViewData["Title"] = "CreateIndex";
    }
   
    <div class="row">
        <div class="col-md-4">
            <form asp-action="CreateIndex">
                <div asp-validation-summary="ModelOnly" class="text-danger"></div>
                <div class="form-group">
                    <label asp-for="Name" class="control-label"></label>
                    <input asp-for="Name" class="form-control" />
                    <span asp-validation-for="Name" class="text-danger"></span>
                </div>
                <div class="form-group"> 
                        <label asp-for="CategoryTypeId" class="control-label">Category Type</label> 
                        <select asp-for="CategoryTypeId" asp-items="ViewBag.CategoryId" class="form-control">
                            <option value="">Select Category</option>
                        </select>  
                </div>
                <div class="form-group"> 
                        <label asp-for="SubCategoryTypeId" class="control-label">SubCategory Type</label> 
                        <select asp-for="SubCategoryTypeId" class="form-control"></select> 
                </div>
                <div class="form-group">
                    <input type="submit" value="Create" class="btn btn-primary" />
                </div>
            </form>
        </div>
    </div>
   
    @section Scripts{ 
    <script>
        $(function () {
            $("select#CategoryTypeId").change(function () {
                var cid = $(this).val();
   
                $("select#SubCategoryTypeId").empty();
   
                $.getJSON(`/Home/GetSubCategory?cid=${cid}`, function (data) {
                    //console.log(data);
                    $.each(data, function (i, item) {
                        $("select#SubCategoryTypeId").append(`<option value="${item.id}">${item.name}</option>`);
                    });
                });
            })
        });
    </script>
    }
   

截图如下：