Asp.net mvc 将viewbag传递给@Dropdownlist

我正在尝试将查看包传递给DropDownList，但不起作用

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

下拉列表错误

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

看法

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

如果我让下拉列表以这种方式显示@Html.DropDownList（“TransporteId”，null，htm。。。。 如果在控制器中抛出else方法，则返回if

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

如何解决此问题？

替换

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

与

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

@Html.DropDownList("TransporteId", (IEnumerable<SelectListItem>)ViewBag.BanhoTosaId,null, new { @class = "form-control" })

@Html.DropDownList（“TransporteId”，（IEnumerable）ViewBag.BanhoTosaId，null，new{@class=“form control”}）

您需要强制转换ViewBag.BanhoTosaId:

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

 @Html.DropDownList("TransporteId", (List<SelectList>) ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

借

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

然后在razor视图中添加：

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

@Html.DropDownList("TransporteId", new SelectList(ViewBag.TransporteId , "TransporteId", "Tipo"))

---

您首先需要从数据中创建一个列表，您希望通过它填充列表，如下所示：

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

List<Category> CatList = db.Categories.ToList();

之后，您将查看并编写：

 @Html.DropDownList("TransporteId", ViewBag.BanhoTosaId, htmlAttributes: new { @class = "form-control" })

@Html.DropDownListFor（model=>model.CategoryID，ViewBag.CategoriesList作为SelectList，
“选择类别”，新建{@class=“form control”}）
@Html.ValidationMessageFor（model=>model.CategoryID，“，new{@class=“text danger”}）

你到底想在这里做什么？如果（ViewBag.BanhoTosaId！=null和&ViewBag.SelectedValue！=null）既然你刚刚设置了它们，而且它们永远都不能为

null

首先你需要在你的方法中强制转换SelectList-

@Html.DropDownList（“TransporteId”，（IEnumerable）ViewBag.BanhoTosaId

..}`但这没有任何意义，因为您试图绑定到

TransporteId

，而不是

BanhoTosaId

。但这也不会起作用（从阅读开始理解。停止使用视图包并使用视图模型）