使用 C# 在 ASP.NET MVC 中单击后 DropDownList 所选项目发生更改

Question

模型类：

public class NewsCategoriesModel 
{
    public int NewsCategoriesID { get; set; }        
    public string NewsCategoriesName { get; set; }
}

控制器：

public ActionResult NewsEdit(int ID, dms_New dsn) 
{
    dsn = (from a in dc.dms_News where a.NewsID == ID select a).FirstOrDefault();
    var categories = (from b in dc.dms_NewsCategories select b).ToList();
    var selectedValue = dsn.NewsCategoriesID;
    SelectList ListCategories = new SelectList(categories, "NewsCategoriesID", "NewsCategoriesName",selectedValue);

    // ViewBag.NewsCategoriesID = new SelectList(categories as IEnumerable<dms_NewsCategory>, "NewsCategoriesID", "NewsCategoriesName", dsn.NewsCategoriesID);
    ViewBag.NewsCategoriesID = ListCategories;
    return View(dsn);
}

查看：

@using (Html.BeginForm("Index", "Home", FormMethod.Post))
{
        <div>
            @Html.DropDownList("Students", (SelectList)ViewBag.students, new { @class = "form-control" })
        </div>
        <input type="submit" value="Select" id="Submit" class="btn btn-default"  />
}

但是我仍然没有停止在下拉列表中选择的值

Answer 1

我在页面顶部添加视图页面模型声明

@model WebApplication4.Models.Student

然后使用 'DropDownListFor' 而不是 'DropDownList'

<div class="col-md-4">
        <h2>Getting started</h2>
        @using (Html.BeginForm("Index", "Home", FormMethod.Post))
        {
        <div>
            @Html.DropDownListFor(model => model.Id, (IEnumerable<SelectListItem>)ViewBag.students, new { @class = "form-control" })
        </div>
        <input type="submit" value="Select" id="Submit" class="btn btn-default"  />
        }
    </div>

之后，当我们单击事件触发时，所选值不会更改。 :-)