Asp.net MVC 5, Identity 2.0 Unable to add a Role to user

Question

i am trying to add a role to a specific user using controllers. But, i am getting error

Here my Role Controller:

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult RoleAddToUser(string UserName, string RoleName)
{
    ApplicationUser user = context.Users.Where(u => u.UserName.Equals(UserName, StringComparison.CurrentCultureIgnoreCase)).FirstOrDefault();
    var account = new AccountController();
    account.UserManager.AddToRole(user.Id, RoleName);

    ViewBag.ResultMessage = "Role created successfully !";

    // prepopulat roles for the view dropdown
    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");
}    

Here is my Action Controller:

public class AccountController : Controller
{
    private ApplicationUserManager _userManager;

    public AccountController()
    {
    }

    public AccountController(ApplicationUserManager userManager, ApplicationSignInManager signInManager )
    {
        UserManager = userManager;
        SignInManager = signInManager;
    }

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

This is the error i am getting:

Server Error in '/' Application.

Object reference not set to an instance of an object.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 32:             get
Line 33:             {
Line 34:                 return _userManager ??      HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
Line 35:             }
Line 36:             private set

Answer 1

Try this,

Add Rolemanger class property and add in AccountController.

 public AccountController(ApplicationUserManager userManager, ApplicationSignInManager signInManager, ApplicationRoleManager roleManager)
 {
        UserManager = userManager;
        SignInManager = signInManager;
       RoleManager =roleManager;
 }

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

After add this in your page. user this assign role to user. pass your user's id userId and rolename which role you want to assign to user.

var result = UserManager.AddToRole(userId, "RoleName");