C# 如何在asp.net mvc 4中从SelectList中获取项目

我正在创建一个自定义的注册表单，只供网站管理员使用。在这个注册表单中，管理员可以添加用户并赋予他们在网站中的角色，所以我创建了这个模型来定义from

public class AddUserToRoleModels
{
    [Required]
    [Display(Name = "User name")]
    public string UserName { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [Required]
    [DataType(DataType.Password)]
    [Display(Name = "Confirm password")]
    [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }

    [Required]
    [Display(Name = "Select Role")]
    public string Roles { get; set; }
}

并使该方法在类函数中添加用户并赋予他们角色

public class Functions
{
    public void AddUserToRole(string UserName,string PassWord,string Role) {

        if (!WebSecurity.UserExists(UserName))
            WebSecurity.CreateUserAndAccount(UserName, PassWord);

        if (!Roles.GetRolesForUser(UserName).Contains(Role))
            Roles.AddUsersToRoles(new[] { UserName }, new[] { Role });
    }
}

然后我创建这个控制器

public class AddUserToRoleController : Controller
{
    UsersContext db = new UsersContext();

    public ActionResult Create()
    {
        ViewBag.RoleId = new SelectList(db.Roles, "RoleId", "RoleName");
        return View();
    }

    [HttpPost]
    public ActionResult Create(AddUserToRoleModels model)
    {
        if (ModelState.IsValid)
        {
            Functions ob = new Functions();

            ob.AddUserToRole(model.UserName, model.Password, model.Roles);

            return RedirectToAction("Index");
        }

        ViewBag.RoleId = new SelectList(db.Roles, "RoleId", "RoleName");
            return View(model);

    }
 }

using (UsersContext db = new UsersContext()){ var tmp = db.Roles.ToList(); ViewBag.RoleId = new SelectList(tmp, "RoleId", "RoleName"); } 并为创建动作控制器创建视图

@model SeniorProject.Models.AddUserToRoleModels

@{
    ViewBag.Title = "Create";
}

 <h2>Create</h2>

 @using (Html.BeginForm()) {
@Html.ValidationSummary(true)

<fieldset>
    <legend>AddUserToRoleModels</legend>

    <div class="editor-label">
        @Html.LabelFor(model => model.UserName)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.UserName)
        @Html.ValidationMessageFor(model => model.UserName)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.Password)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.Password)
        @Html.ValidationMessageFor(model => model.Password)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.ConfirmPassword)
    </div>
    <div class="editor-field">
        @Html.EditorFor(model => model.ConfirmPassword)
        @Html.ValidationMessageFor(model => model.ConfirmPassword)
    </div>

    <div class="editor-label">
        @Html.LabelFor(model => model.Roles)
    </div>
    <div class="editor-field">
        @Html.DropDownList("RoleId", String.Empty)
        @Html.ValidationMessageFor(model => model.Roles)
    </div>

    <p>
        <input type="submit" value="Create" />
    </p>
</fieldset>

  }

<div>
   @Html.ActionLink("Back to List", "Index")
</div>

 @section Scripts {
   @Scripts.Render("~/bundles/jqueryval")
}

当我尝试添加新用户并给他角色时，用户插入到数据库中，但没有角色，我认为因为我试图从@Html.DropDownListRoleId获取角色，String.Empty，它是list and my method，它为角色使用字符串参数，我尝试从此列表中获取所选项目，但无法工作，因此请帮助

@Html.DropDownListFor(model => model.RoleID, ViewBag.RoleID, "")

或者类似的东西

您也可以将该列表作为selectList放到viewmodel中，然后将其称为Model。RoleIDs

试试以下方法：

public ActionResult Create()
{
    ViewBag.Roles = new SelectList(db.Roles, "RoleId", "RoleName");
    return View();
}

鉴于：

@Html.DropDownListFor(model => model.RoleId, ViewBag.Roles as IEnumerable<SelectListItem>, "Select a role" )

在操作后ifmodel.RoleId==0，因此您不选择任何角色。

在控制器中

public class AddUserToRoleController : Controller
{
    UsersContext db = new UsersContext();

    public ActionResult Create()
    {
        ViewBag.RoleId = new SelectList(db.Roles, "RoleId", "RoleName");
        return View();
    }

    [HttpPost]
    public ActionResult Create(AddUserToRoleModels model)
    {
        if (ModelState.IsValid)
        {
            Functions ob = new Functions();

            ob.AddUserToRole(model.UserName, model.Password, model.Roles);

            return RedirectToAction("Index");
        }

        ViewBag.RoleId = new SelectList(db.Roles, "RoleId", "RoleName");
            return View(model);

    }
 }

using (UsersContext db = new UsersContext()){ var tmp = db.Roles.ToList(); ViewBag.RoleId = new SelectList(tmp, "RoleId", "RoleName"); }

---

您需要将RoleID绑定到int字段。在Ryan的回答中，dropdownlist值将以编写代码的方式绑定到模型属性int RoleId，如果将int RoleId添加到创建方法的参数列表中，它将绑定到该属性。在创建httppost操作中，角色id是否与模型一起发布？