asp.net-mvc - 在 View 中生成时 SelectList 不选择项目

Question

在 View 中创建 SelectList 时，我在预选项目时遇到问题。这是剃刀代码：

@{
    ViewBag.Title = "RoleGroupMappings";
}

<h2>Map roles to groups:</h2>

<table>
    @foreach (var role in Model.Roles)
    {
        <tr>
            <td>
                <p>@role.RoleName: </p>
            </td>
            <td>
                @using (Html.BeginForm("MapGroupsToRole", "Role", FormMethod.Post))
                {
                    @Html.AntiForgeryToken()
                    @Html.Hidden("RoleId", role.RoleId)

                    @Html.DropDownList("Groups", new SelectList(role.Groups, "GroupId", "GroupName", role.Groups.Where(g => g.Mapped).Select(g => g.GroupId)), new { @class = "directory-groups", multiple = "multiple", style = "display: none;" })
                    <input type="button" value="Clear All" class="btn btn-danger clear-selection" />
                    <input type="submit" value="Save Changes" class="btn btn-success save-mappings" />
                }
            </td>
        </tr>
    }
</table>

有人知道这里有什么问题吗？

Answer 1

I think you want to be using a MultiSelectList instead of the normal SelectList. Try this:

@Html.DropDownList("Groups", new MultiSelectList(role.Groups, "GroupId", "GroupName", role.Groups.Where(g => g.Mapped).Select(g => g.GroupId)), new { @class = "directory-groups", multiple = "multiple", style = "display: none;" })

Update

Being as this is working for me here, I'll show you how I've setup this test project. Hopefully that will help you to narrow down what the problem is. Test model setup:

public class Role
{
    public int RoleId { get; set; }
    public string RoleName { get; set; }
    public List<Group> Groups { get; set; }
}

public class Group
{
    public Guid GroupId { get; set; }
    public string GroupName { get; set; }
    public bool Mapped { get; set; }
}

The view model:

public class TestViewModel
{
    public List<Role> Roles { get; set; }
}


public ActionResult Index()
{
    var model = new TestViewModel
    {
        Roles = new List<Role>
        {
            new Role
            {
                RoleId = 1,
                RoleName = "Test",
                Groups = new List<Group>
                {
                    new Group
                    {
                        GroupId = new Guid("12345678-1234-1234-1234-123412341234"),
                        GroupName = "Group 1",
                        Mapped = false
                    },
                    new Group
                    {
                        GroupId = new Guid("12345678-5678-6789-1234-123412341234"),
                        GroupName = "Group 2",
                        Mapped = true
                    },
                    new Group
                    {
                        GroupId = new Guid("12345678-0000-6789-1234-123412341234"),
                        GroupName = "Group 3",
                        Mapped = true
                    }
                }
            }
        }
    };

    return View(model);
}

My view is the same as yours, except with using MultiSelect and I also removed @class = "directory-groups" and the display: none; style. Both group 2 and group 3 have their Mapped property set to true. This is the result from loading the view:

Answer 2

我发现我的控制器有问题。我将 ViewBag.Groups 设置为一些值，显然它干扰了我的同名 DropDownList。抱歉，我盯着一整天都找不到错误，所以我有点绝望。我也应该看看我的控制器。