获取 MVC ASP.NET 中的角色列表

Question

我有以下方法来获取存储在AspNetRoles中的角色列表

    [AllowAnonymous]
    public async Task<ActionResult> Register()
    {
        //Get the list of Roles
        ViewBag.RoleId = new SelectList(await RoleManager.Roles.ToListAsync(), "Name", "Name");
        return View();
    }

然后我得到如下视图

    <div class="form-group">
        <label class="col-md-2 control-label">
            Select User Role
        </label>
        <div class="col-md-10">
            @foreach (var item in (SelectList)ViewBag.RoleId)
            {
                <input type="checkbox" name="SelectedRoles" value="@item.Value" class="checkbox-inline" />
                @Html.Label(item.Value, new { @class = "control-label" })
            }
        </div>
    </div>

但是一旦我加载页面，我就会收到Object reference not set to an instance of an object.错误

第 175 行：ViewBag.RoleId = new SelectList（await RoleManager.Roles.ToListAsync（）， "Name"， "Name"）;

这是RoleManager定义

    public ApplicationRoleManager RoleManager
    {
        get
        {
            return _roleManager ?? HttpContext.GetOwinContext().Get<ApplicationRoleManager>();
        }
        private set
        {
            _roleManager = value;
        }
    }

这是ApplicationRoleManager模型

// Configure the RoleManager used in the application. RoleManager is defined in the ASP.NET Identity core assembly
public class ApplicationRoleManager : RoleManager<ApplicationRole>
{
    public ApplicationRoleManager(IRoleStore<ApplicationRole, string> roleStore)
        : base(roleStore)
    {
    }
    public static ApplicationRoleManager Create(IdentityFactoryOptions<ApplicationRoleManager> options, IOwinContext context)
    {
        return new ApplicationRoleManager(new ApplicationRoleStore(context.Get<ApplicationDbContext>()));
    }
}

Answer 1

在 Startup.Auth 中，像这样引用 RoleManager：

    public void ConfigureAuth(IAppBuilder app)
    {
        // Add this reference
        app.CreatePerOwinContext<ApplicationRoleManager>(ApplicationRoleManager.Create);
    }

确保控制器包含以下构造函数：

        // Include this
        private ApplicationRoleManager _roleManager;
        // You already have this
        public ApplicationRoleManager RoleManager { get { return _roleManager ?? HttpContext.GetOwinContext().Get<ApplicationRoleManager>(); } private set { _roleManager = value; } }

重建，再试一次，希望这会解决它。

Answer 2

检查您的RoleManager.Roles属性。似乎它没有从数据库返回任何内容。还要确保表中至少有一个角色实体UserRoles