无法在WebApi控制器中实例化UserManager

Question

我无法在WebApi Controller中实例化UserManager，我找到了各种答案here，here

也是。我已经尝试了所有，但仍然没有解决。

这是我的代码：

public class CampaignController : ApiController
{
    private ApplicationUserManager _userManager;
    private ApplicationSignInManager _signInManager;
    public CampaignController()
    {
    }
    public CampaignController(ApplicationUserManager userManager, ApplicationSignInManager signInManager)
    {
        UserManager = userManager;
        SignInManager = signInManager;
    }

    public ApplicationUserManager UserManager
    {
        get
        {
            return _userManager ?? Request.GetOwinContext().GetUserManager<ApplicationUserManager>();
        }
        private set
        {
            _userManager = value;
        }
    }
    public ApplicationSignInManager SignInManager
    {
        get
        {
            return _signInManager ?? HttpContext.Current.GetOwinContext().Get<ApplicationSignInManager>();
        }
        private set
        {
            _signInManager = value;
        }
    }

    [HttpPost]
    [Route("savesync")]
    public object SaveSync(AsaanAccountCampaignInfo model)
    {
        try
        {
            var user = new ApplicationUser { UserName = model.MobileNumber, PhoneNumber = model.MobileNumber, Email = model.EmailAddress, VerificationCode = VerificationCode, CreatedBy = "Local System" };
            var result = UserManager.Create(user, "default123");
            if (result.Succeeded)
            {
                 return new { status = true, message = "Record Added Succefully." };
            }
        }
        catch (Exception e)
        {
            throw e;
        }
    }
  }

它将在以下位置抛出Null引用异常： UserManager.Create（用户，“ default123”）;