Question

我创建了一个控制器，该控制器接受查询字符串中的一个参数，该参数是整数，并且我有一个下拉列表，我想基于该参数值从列表中设置一个默认值，但它不起作用。我正在使用DropDownListFor html帮助程序来创建列表。

这是我的控制人：

public ActionResult Index(int accountType)
        {
            List<SelectListItem> listItems = new List<SelectListItem>
            {
                new SelectListItem{Text = "Competitor",Value = "Competitor"},
                new SelectListItem{Text = "Consultant",Value = "Consultant"},
                new SelectListItem{Text = "Customer",Value = "Customer"},
                new SelectListItem{Text = "Investor",Value = "Investor"},
                new SelectListItem{Text = "Partner",Value = "Partner"},
                new SelectListItem{Text = "Influencer",Value = "Influencer"},
                new SelectListItem{Text = "Press",Value = "Press"},
                new SelectListItem{Text = "Prospect",Value = "Prospect"},
                new SelectListItem{Text = "Reseller",Value = "Reseller"},
                new SelectListItem{Text = "Supplier",Value = "Supplier"},
                new SelectListItem{Text = "Vendor",Value = "Vendor"},
                new SelectListItem{Text = "Other",Value = "Other"}
            };

            Account account = new Account
            {
                Name = "khaled",
                Email = "test",
                AccountType = listItems[accountType].Text
            };
            ViewBag.items = listItems;
            return View(account);
        }

我的观点： @using System.Globalization @model Form_Task.Models.Account

<div class="form-group">
       @Html.Label("accounttype", "Account Type")
       @Html.DropDownListFor(Model=>Model.AccountType,(List<SelectListItem>)ViewBag.items,new{@class = "form-control", @disabled="disabled"})
</div>

我的模特：

public class Account
    {
        public string Name { get; set; }
        public string Email { get; set; }
        public string AccountType { get; set;}
    }

如果我将accountType更改为字符串并按如下所示创建模型，则效果很好：

Account account = new Account
                {
                    Name = "khaled",
                    Email = "test",
                    AccountType = accountType
                };

Answer 1

从您的评论看来，您似乎想根据其在列表中的位置来设置选定的值...如果必须这样做，那么在将其传递到视图包之前，此代码将起作用。

        Account account = new Account
        {
            Name = "khaled",
            Email = "test",
            AccountType = listItems[accountType].Text
        };

        listItems[accountType].Selected = true;//Add this line
        ViewBag.items = listItems;
        return View(account);

但是，这不是一个好的处理方法，如果顺序发生变化会怎样？如果从查询字符串中获得的int的长度大于listItems的长度，会发生什么？

更典型的方法是根据selected的值来设置SelectListItem，如下所示：

public ActionResult Index(string accountType)//pass through the listitems value instead of its position in the list.
{
    List<SelectListItem> listItems = new List<SelectListItem>
        {
            new SelectListItem{Text = "Competitor",Value = "Competitor"},
            new SelectListItem{Text = "Consultant",Value = "Consultant"},
            new SelectListItem{Text = "Customer",Value = "Customer"},
            new SelectListItem{Text = "Investor",Value = "Investor"},
            new SelectListItem{Text = "Partner",Value = "Partner"},
            new SelectListItem{Text = "Influencer",Value = "Influencer"},
            new SelectListItem{Text = "Press",Value = "Press"},
            new SelectListItem{Text = "Prospect",Value = "Prospect"},
            new SelectListItem{Text = "Reseller",Value = "Reseller"},
            new SelectListItem{Text = "Supplier",Value = "Supplier"},
            new SelectListItem{Text = "Vendor",Value = "Vendor"},
            new SelectListItem{Text = "Other",Value = "Other"}
        };

        //loop through and check for a match
        foreach (var item in listItems)
        {
            item.Selected = item.Value == accountType;
        }

        Account account = new Account
        {
            Name = "khaled",
            Email = "test",
            AccountType = listItems[accountType].Text
        };
        ViewBag.items = listItems;
        return View(account);
}

这样，如果值与查询字符串不匹配，则不会引起异常，并且您的方法仍将完成。

编辑-刚注意到您正在使用@Html.DropDownListFor()，请将其更改为@Html.DropDownList()或将其更改为html5控件，否则Selected属性将被忽略。

<div class="form-group">
   @Html.Label("accounttype", "Account Type")
   <select name="AccountType" class="form-control" disabled="disabled">
       @foreach(var item in (List<SelectListItem>)ViewBag.items)
       {
       <option value='@item.Value' @(item.Selected ? "selected" : "")>@item.Text</option> 
       }
   </select>
</div>

在DropDownListFor中选择默认值对于HTML助手不起作用-ASP .NET MVC

1 个答案: