asp.net-mvc – SelectList选择的值未转移到DropDownList

我有一个Razor页面,其中包含一个表单内的下拉列表：

@using (Html.BeginForm("ProductsByOwners", "Report", FormMethod.Post, new { @id = "ProductsByOwners" }))
{            
    @Html.Label("Choose product owner: ")
    @Html.DropDownList("OwnerList", (SelectList)ViewBag.OwnerList, new { @onchange = "this.form.submit();" })    
}

我的SelectList的选定值未被转移到DropDownList.我调试并逐步完成代码,发现(SelectList)ViewBag.OwnerList正确评估并选择了预期值,但生成的HTML没有选择任何选项标签.

谁能看到我在这里做错了什么？

更新

以下是在我的操作中如何创建SelectList：

ViewBag.OwnerList = new SelectList(ListUtils.ProductOwners(), "Key", "Value", values["OwnerList"]);

结果具有由值[“OwnerList”]指示的值.

谢谢！

您没有正确使用DropDownList帮助程序.要创建下拉列表,您需要两件事：

>提交表单时绑定到所选值的标量属性
>将选项绑定到的集合

在您的示例中,您只有这两件事中的一件(第二件).您的第一个参数称为OwnerList,并且您将ViewBag.OwnerList作为第二个参数传递.

所以：

@Html.DropDownList(
    "SelectedOwnerId", 
    (SelectList)ViewBag.OwnerList, 
    new { @onchange = "this.form.submit();" }
)

显然我会建议你使用强类型视图和视图模型.显然摆脱了弱类型的ViewBag / ViewData / ViewCrap.

首先,设计一个视图模型以满足视图的要求(从目前为止显示的是显示下拉列表)：

public class OwnerViewModel
{
    [DisplayName("Choose product owner: ")]
    public string SelectedOwnerId { get; set; }

    public IEnumerable<SelectListItem> OwnerList { get; set; }
}

然后一个控制器：

public class ReportController: Controller
{
    public ActionResult ProductsByOwners()
    {
        var model = new OwnerViewModel
        {
            // preselect the second owner
            SelectedOwnerId = "2",

            // obviously those come from your database or something
            OwnerList = new[] 
            {
                new SelectListItem { Value = "1", Text = "owner 1" },
                new SelectListItem { Value = "2", Text = "owner 2" },
                new SelectListItem { Value = "3", Text = "owner 3" },
            }
        };
        return View(model);
    }

    [HttpPost]
    public ActionResult ProductsByOwners(OwnerViewModel model)
    {
        ...
    }
}

并且您有一个相应的强类型视图：

@model OwnerViewModel
@using (Html.BeginForm("ProductsByOwners", "Report", FormMethod.Post, new { id = "ProductsByOwners" }))
{            
    @Html.LabelFor(x => x.SelectedOwnerId)
    @Html.DropDownListFor(
        x => x.SelectedOwnerId, 
        Model.OwnerList, 
        new { onchange = "this.form.submit();" }
    )
}