Html.DropDownList 默认值 MVC 5

Question

我只是想在这个列表中添加一个默认值（“创建新地点”），它可能比我做的更容易。我对方法重载感到困惑，特别是因为我正在使用的重载（由脚手架创建）是 DropDownList(string name, IEnumerable selectList, object htmlAttributes) 并且第二个参数为 null，但它有效。我认为这里有一些约定。谁能阐明这一点和/或如何向此列表添加默认值？

控制器：

ViewBag.VenueId = new SelectList(db.Venues, "Id", "Name", review.VenueId);
        return View(review);
    }   

查看：

<div class="form-group">
        @Html.LabelFor(model => model.VenueId, "VenueId", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownList("VenueId", null, htmlAttributes: new { @class = "form-control" })
            @Html.ValidationMessageFor(model => model.VenueId, "", new { @class = "text-danger" })
            <div>Don't see what you're looking for?  Fear not.  Just type in the name and create your review; we'll fill in the rest!</div>
        </div>
</div>

Answer 1

也许您可以分解您的 SelectList 并在其中插入一个项目？这是一个示例（尚未对其进行测试，因此不能 100% 确定它是否有效）：

控制器

// Create item list from your predefined elements
List<SelectListItem> yourDropDownItems = new SelectList(db.Venues, "Id", "Name", review.VenueId).ToList();

// Create item to add to list
SelectListItem additionalItem = new SelectListItem { Text = "Create new Venue", Value = "0" }; // I'm just making it zero, in case you want to be able to identify it in your post later

// Specify index where you would like to add your item within the list
int ddIndex = yourDropDownItems.Count(); // Could be 0, or place at end of your list?

// Add item at specified location
yourDropDownItems.Insert(ddIndex, additionalItem);

// Send your list to the view
ViewBag.DropDownList = yourDropDownItems;

return View(review);

查看

@Html.LabelFor(model => model.VenueId, new { @class = "form-control" })
    <div>
        @Html.DropDownListFor(model => model.VenueId, ViewBag.DropDownList)
        @Html.ValidationMessageFor(model => model.VenueId)
    </div>
</div>

编辑：

您应该能够添加默认值的一种方法是在 .DropDownListFor 的最后一个参数中，如下所示：

@Html.DropDownListFor(model => model.VenueId, ViewBag.DropDownList, "Create new Venue")