asp.net-mvc - ASP.NET 身份 2.0 RoleManager.Roles 'Object reference not set to an instance of an object.'

Question

我正在将 ASP.NET Identity 2.0 与 ASP.NET MVC 5 和 EF 6 项目结合使用。

我正在尝试编辑与用户关联的角色。

在我的用户管理 Controller 中，我有:

    //
    // GET: /Users/Edit/1
    public async Task<ActionResult> Edit(string id)
    {
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        var user = await UserManager.FindByIdAsync(id);
        if (user == null)
        {
            return HttpNotFound();
        }

        var userRoles = await UserManager.GetRolesAsync(user.Id);

        return View(new EditUserViewModel()
        {
            Id = user.Id,
            Email = user.Email,
            RolesList = RoleManager.Roles.ToList().Select(x => new SelectListItem()
            {
                Selected = userRoles.Contains(x.Name),
                Text = x.Name,
                Value = x.Name
            })
        });
    }

我收到错误

'Object reference not set to an instance of an object.'

行:

return View(new EditUserViewModel()

当我尝试时:

    //
    // GET: /Users/Edit/1
    public async Task<ActionResult> Edit(string id)
    {
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }

        ViewBag.RoleId = new SelectList(RoleManager.Roles, "Id", "Name");

        var user = await UserManager.FindByIdAsync(id);
        if (user == null)
        {
            return HttpNotFound();
        }
        return View("EditUser", user);
    }

我收到错误

'Object reference not set to an instance of an object.'

行:

ViewBag.RoleId = new SelectList(RoleManager.Roles, "Id", "Name");

我是否缺少配置设置？

在 Controller 的开头我定义:

    public UserManagementController(ApplicationUserManager userManager, ApplicationRoleManager roleManager)
    {
        UserManager = userManager;
        RoleManager = roleManager;
    }

    private ApplicationUserManager _userManager;
    public ApplicationUserManager UserManager
    {
        get
        {
            return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
        }
        private set
        {
            _userManager = value;
        }
    }

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

Answer 1

正如我们发现的，问题是您忘记为每个请求创建一个 ApplicationRoleManager 实例。添加app.CreatePerOwinContext<ApplicationRoleManager>(ApplicationRoleManager.Create);到 App_Start/Startup.Auth.cs 就可以了。 :)