MVC5客戶控制器空引用異常

Question

我正在嘗試在MVC Web應用程序中實現用戶角色。 但是我在return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();的行上得到一個空異常return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>(); return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>(); 在我的帳戶控制器中

客戶總監

[Authorize]
public class AccountController : Controller
{
    private ApplicationSignInManager _signInManager;
    private ApplicationUserManager _userManager;
    private ApplicationRoleManager _roleManager; 

    public AccountController(){}

    public AccountController(ApplicationUserManager userManager, ApplicationSignInManager signInManager, ApplicationRoleManager roleManager)
    {   UserManager = userManager;
        SignInManager = signInManager;
        RoleManager = roleManager; }
    public ApplicationRoleManager RoleManager
    {
        get { return _roleManager ?? HttpContext.GetOwinContext().Get<ApplicationRoleManager>(); }
        private set { _roleManager = value; }
    }

    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; }
    }

將觸發將用戶添加到角色的ActionResult。

    [System.Web.Mvc.HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult RoleAddToUser(string UserName, string RoleName)
    {
        ApplicationUser user = context.Users.FirstOrDefault(u => u.UserName.Equals(UserName, StringComparison.CurrentCultureIgnoreCase));
        var account = new AccountController();
        if (user != null) account.UserManager.AddToRole(user.Id, RoleName);
        var list = context.Roles.OrderBy(r => r.Name).ToList().Select(rr => new SelectListItem { Value = rr.Name.ToString(), Text = rr.Name }).ToList();
        ViewBag.Roles = list;
        return View("ManageUserRoles");
    }

Startup.Auth確實包含

        app.CreatePerOwinContext(ApplicationDbContext.Create);
        app.CreatePerOwinContext<ApplicationRoleManager>(ApplicationRoleManager.Create);
        app.CreatePerOwinContext<ApplicationUserManager>(ApplicationUserManager.Create);
        app.CreatePerOwinContext<ApplicationSignInManager>(ApplicationSignInManager.Create);

身份配置

    // Configure the application sign-in manager which is used in this application.
public class ApplicationSignInManager : SignInManager<ApplicationUser, string>
{
    public ApplicationSignInManager(ApplicationUserManager userManager, IAuthenticationManager authenticationManager)
        : base(userManager, authenticationManager)
    {
    }

    public override Task<ClaimsIdentity> CreateUserIdentityAsync(ApplicationUser user)
    { return user.GenerateUserIdentityAsync((ApplicationUserManager)UserManager); }

    public static ApplicationSignInManager Create(IdentityFactoryOptions<ApplicationSignInManager> options, IOwinContext context)
    { return new ApplicationSignInManager(context.GetUserManager<ApplicationUserManager>(), context.Authentication); }
}
public class ApplicationRoleManager : RoleManager<IdentityRole>
{
    public ApplicationRoleManager(IRoleStore<IdentityRole, string> roleStore)
        : base(roleStore) { }

    public static ApplicationRoleManager Create(IdentityFactoryOptions<ApplicationRoleManager> options, IOwinContext context)
    {
        return new ApplicationRoleManager(new RoleStore<IdentityRole>(context.Get<ApplicationDbContext>()));
    }
}

空引用來自哪里？ 在代碼中，我再次檢查用戶是否存在。

謝謝

Answer 1

這些無疑是令人反感的線...

var account = new AccountController();
if (user != null) account.UserManager.AddToRole(user.Id, RoleName);

並不是要以這種方式實例化控制器，因為它們與當前的HTTP請求（因此HttpContext ）緊密相關。

當HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>(); 被擊中， HttpContext為空，因為沒有上下文。

您可以在試圖訪問UserManager的控制器中簡單地放置相同的屬性。 之所以可行，是因為OwinContext在整個應用程序中共享。

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

    public ActionResult RoleAddToUser(string UserName, string RoleName)
    {
        ApplicationUser user = context.Users.FirstOrDefault(u => u.UserName.Equals(UserName, StringComparison.CurrentCultureIgnoreCase));
        if (user != null) UserManager.AddToRole(user.Id, RoleName);

        //Other code...

        return View("ManageUserRoles");
    }
}

而且，如果您真的想花哨的話，請聲明一個繼承自Controller的BaseController ，將UserManager屬性放入其中，並使所有其他控制器都繼承自您的基礎。