ASP.NET MVC Razor：将空值添加到DropDownList

Question

I tried for hours to get it work, but now I have to ask..

As read in
/942262/add-empty-value-to-a-dropdownlist-in-asp-net-mvc and /3780614/mvc-clear-default-selected-value-of-selectlist
I want to add an empty space to dropdown lists in my ASP.NET MVC Razor WebApp with Entity Framework 5 to force the user for an input.

I followed the informations, but what happend in the View is that: http://i.stack.imgur.com/EXSgT.png
So, as you see, there is an empty space, but it isn't selected by default. Instead, my "testproject", as first value from my controller, is marked.. Not the empty space. So where did I fail?

Thanks a lot.

My model looks like that:

    [...]
    using System.Web.Mvc;

    public class UploadTranferContainer
    {    
         [DisplayName("Project")]
         public int ProjectID { get; set; }

         public SelectList Projects { get; set; }
    }

My controller fills the data in like:

    UploadTranferContainer container = new UploadTranferContainer();
    container.Projects = new SelectList(db.Projects.AsEnumerable(), "ProjectID", "ProjectName");

And the view unpacks my container like:

        <div class="editor-label metadataLabel">
            @Html.LabelFor(x => x.ProjectID)
        </div>
        <div class="editor-field">
            @Html.DropDownListFor(x => x.ProjectID, Model.Projects, string.Empty)
        </div>            

Answer 1

The selected value of the dropdown will be the value (if found) of Model.ProjectID

If you want this to appear as the first (empty) option of the select, make sure the value of ProjectID is not contained in the select list items Model.Projects

Answer 2

您可以使用以下方法下拉空值

@Html.DropDownListFor(x => x.ProjectID, new SelectList(Model.Projects, "ProjectID", "ProjectName"), " ")

Answer 3

Allows to create a empty list item

var area = new[] { new tbl_Area { AreaID = -1, AreaName = "Please Select Main Area" } };

or

ViewBag.SubAreaList = new[] { new tbl_Area { AreaID = -1, AreaName = "Please Select Main Area" } };

razor

@Html.DropDownList("DdlSubAreas", new SelectList(ViewBag.SubAreaList, "AreaID", "AreaName"), new { size = "10" });

tbl_Area can be a class or datamodel

class tbl_Area{
   public int AreaID {get;set;}
   public string AreaName {get;set;}
}