视图模型未与 DropDownListFor 绑定答案

【问题标题】：View Model Not Binding with DropDownListFor视图模型未与 DropDownListFor 绑定
【发布时间】：2016-12-13 17:01:05
【问题描述】：

我试图让一个由视图模型填充的下拉列表，然后在 HTTPPOST 上尝试检索选定的值，但模型在 post 的控制器中没有绑定数据。任何帮助，将不胜感激。

查看模型

public class TransferViewModel
{

    public IEnumerable<User> Users { get; set; }
    public string SortOrder { get; set; }
    public SelectList Departments { get; set; }
    public SelectList Sites { get; set; }

    public SelectListItem SelectedDepartment { get; set; }
    public SelectListItem SelectedSite { get; set; }
    public User SelectedUser { get; set; }
}

控制器

public ActionResult Sort(TransferViewModel model)
    {
        var users = from s in _db.Users select s;
        var departments = new SelectList(_db.Departments);
        var sites = new SelectList(_db.Sites);
        model.Departments = departments;
        model.Sites = sites;

        if (model.SelectedDepartment != null)
        {
            users = users.Where(s => s.Department.ID == Convert.ToInt32(model.SelectedDepartment));
        }
        else if (model.SelectedSite != null)
        {
            users = users.Where(s => s.Site.ID == Convert.ToInt32(model.SelectedSite));
        }

        switch (model.SortOrder)
        {
            case "name_desc":
                users = users.OrderByDescending(s => s.LName);
                break;
            case "dept":
                users = users.OrderBy(s => s.Department.Name);
                break;
            case "dept_desc":
                users = users.OrderByDescending(s => s.Department.Name);
                break;
            case "site":
                users = users.OrderBy(s => s.Site.Name);
                break;
            case "site_desc":
                users = users.OrderByDescending(s => s.Site.Name);
                break;
            default:
                users = users.OrderBy(s => s.LName);
                break;
        }
        model.Users = users;
        model.Departments = new SelectList(_db.Departments, "ID", "Name", model.SelectedDepartment);
        model.Sites = new SelectList(_db.Sites,"ID","Name", model.SelectedSite);
        return View(model);
    }

查看

@using (Html.BeginForm("Sort", "Transfer", FormMethod.Post ))
{
<p>
    Display by @Html.DropDownListFor(model => model.SelectedDepartment, Model.Departments, htmlAttributes: new { @class = "form-control"})
    Department
</p>
<p>
    or by Location: @Html.DropDownListFor(model => model.SelectedSite, Model.Sites, htmlAttributes: new { @class = "form-control"})

</p>
<p>
    <input type="submit" value="Search"/>
</p>
}

【问题讨论】：

标签： c# asp.net asp.net-mvc

【解决方案1】：

您需要在模型中拥有 int 属性，因为在帖子中，下拉列表的选定 ID 将被发送回控制器：

public class TransferViewModel
{
    ......................
    ......................
    public int SelectedDepartment { get; set; }
    public int SelectedSite { get; set; }
    .....................
    .....................
}

您在操作中告诉自己使用ID 列将下拉列表绑定为DataValueMember：

// see that ID argument there that is binding the value which will be posted back
model.Departments = new SelectList(_db.Departments, "ID", "Name", model.SelectedDepartment);
model.Sites = new SelectList(_db.Sites,"ID","Name", model.SelectedSite);

【讨论】：