OWIN - 对象引用未设置为对象的实例

Question

我正在使用 asp.net mvc 5来开发一个Web应用程序。但是我在玩用户帐户时遇到了一些错误。我创建了一个用户帐户，我想删除它，但在使用 ajax-jquery 执行此操作时面临以下问题。我正在尝试使用 ajax 请求删除用户帐户，但它给出了空对象引用的错误，因为 Owin 上下文由于 ajax 调用而未启动。

 public class AdmissionsController : Controller
 {
    private ApplicationSignInManager _signInManager;
    private ApplicationUserManager _userManager;
    public AdmissionsController()
    {
    }
    public AdmissionsController(ApplicationUserManager userManager, ApplicationSignInManager signInManager)
    {
        UserManager = userManager;
        SignInManager = signInManager;
    }
    public ApplicationSignInManager SignInManager
    {
        get
        {
            return _signInManager ?? HttpContext.GetOwinContext().Get<ApplicationSignInManager>();
        }
        private set
        {
            _signInManager = value;
        }
    }
    public ApplicationUserManager UserManager
    {
        get
        {
            return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
        }
        private set
        {
            _userManager = value;
        }
    }


    //function to delete user account
    public async Task<object> DeleteUser(string id)
    {
        ApplicationDbContext context = new ApplicationDbContext();
        if (id == null)
        {
            return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
        }
        var user = await _userManager.FindByIdAsync(id);
        var logins = user.Logins;
        var rolesForUser = await _userManager.GetRolesAsync(id);
        using (var transaction = context.Database.BeginTransaction())
        {
            foreach (var login in logins.ToList())
            {
                await _userManager.RemoveLoginAsync(login.UserId, new UserLoginInfo(login.LoginProvider, login.ProviderKey));
            }
            if (rolesForUser.Count() > 0)
            {
                foreach (var item in rolesForUser.ToList())
                {
                    // item should be the name of the role
                    var result = await _userManager.RemoveFromRoleAsync(user.Id, item);
                }
            }
            await _userManager.DeleteAsync(user);
            transaction.Commit();
        }
        return new{success=true};
    }

}

我的 ajax 调用如下：

        var userid = $(this).attr("data-StudentId");
        var success = false;


        $.ajax({
            method: "Get",
            url: "/Area/Admissions/DeleteUser",
            data: { "id": userid },
            success: function (response) {
                if (response.Success == true) {
                    success = true;
                }
                else if (response.Success == false) {
                       //window.location.reload();
                }
            },
            error: function (response) {
                notificationMSG("fa fa-thumbs-up", "error", "Error", response.message);
            }
        });

如何解决此问题???我在以下行收到错误：

  var user = await _userManager.FindByIdAsync(id);

Answer 1

这只是

一个疯狂的猜测，但在我看来，你没有实例化_userManager.您有一个相应的属性，用于进行此创建。但是，在有错误的行中，您使用私有字段。尝试使用该属性：

var user = await UserManager.FindByIdAsync(id);

这将调用 getter，从 owin 上下文中获取此管理器。