You should not instantiate your own UserManager, like ever. And it’s actually pretty hard to do so, since it requires you to pass in a lot of arguments to the constructor (and most of those things are also very difficult to set up properly).

不应该再像以前那样实例化UserManager，并且实际上那样做相当困难，因为这样做需要给构造器传递许多参数（并且许多配置要设置恰当是非常困难的）。

ASP.NET Core makes extensive use of dependency injection, so you should just set up your controller in a way that it receives the user manager automatically. That way, you don’t have to worry about creating the user manager:

ASP.NET Core广泛应用了注入技术，所以你应该仅给控制器设置为自动接收user manager。这样做，你就不必考虑创建user manager了。

public class HomeController : Controller
{
    private readonly UserManager<ApplicationUser> userManager;

    public HomeController (UserManager<ApplicationUser> userManager)
    {
        this.userManager = userManager;
    }

    // …
}

However, in order to do that, you first need to set up ASP.NET Identity to actually know about your ApplicationUser and make it be used for storing your user identities. To do that, you need to modify the Startup class. In the ConfigureServices method, you need to change the AddIdentity call to make it reference your actual types:

然而，为了这样做，你首先需要设置ASP.NET Identity，让它知道你的ApplicationUser，并且让他用于存储你的用户身份认证信息。为了实现这个目的，你需要修改Startup类。在ConfigureServices方法中，你需要修改AddIdentity，让它引用你以及的类型：

services.AddIdentity<ApplicationUser, IdentityRole>()
    .AddEntityFrameworkStores<ApplicationDbContext>()
    .AddDefaultTokenProviders();

IdentityRole here refers to the standard role type used by ASP.NET Identity (since you don’t need a custom one). As you can see, we also reference a ApplicationDbContext there which is the entity framework database context for your modified identity model; so we need to set up that one too. In your case, it could just look like this:

这里的IdentityRole指的是ASP.NET Identity标准的角色类型（因为你不需要自定义的角色类型）。这里，我们也引用了ApplicationDbContext，这是用于你修改过的identity模型的数据库上下文；所以，我们也需要做如此设置。针对你的情况，应该是这样：

public class ApplicationDbContext : IdentityDbContext<ApplicationUser>
{
    protected override void OnModelCreating(ModelBuilder builder)
    {
        base.OnModelCreating(builder);

        // here you could adjust the mapping
    }
}

This will make sure that the ApplicationUser entity is actually stored properly in the database. We’re almost done, but we now just need to tell Entity Framework about this database context as well. So again in the ConfigureServices method of your Startup class, make sure to adjust the AddEntityFramework call to also set up the ApplicationDbContext database context. If you have other database contexts, you can just chain these:

这将确保ApplicationUser实体被适当的储存到数据库中。我们几乎完成了，但现在我们仅需要告诉EF这个数据库上下文。所以再一次在Startup类的ConfigureServices方法中，确保调整AddEntityFrameWork，设置为ApplicationDbContext。如果你还有另外的数据库上下文，你可以反复这样做：

services.AddEntityFramework()
    .AddSqlServer()
    .AddDbContext<IdentityContext>(opts => opts.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]))
    .AddDbContext<DataContext>(opts => opts.UseSqlServer(Configuration["Data:DefaultConnection:ConnectionString"]));

And that’s it! Now Entity Framework knows about the new user entity and properly maps it to the database (including your new property), and ASP.NET Identity also knows about your user model and will use that one for everything it does, and you can have the UserManager injected into controllers (or services, or whatever) to do stuff.

这样就完成了。现在EF就知道了新的user实体及其映射到数据库的属性（包含你设置的新属性）；同时ASP.NET Identity也知道了你的user模型，接着就会按照该模型做他该做的事情了，这样你就能将UserManager注入到控制器中工作了。

As for your second error, you get this because the user manager does not have a FindById method; it only as a FindByIdAsync method. You will see this actually in a lot of places with ASP.NET Core that there are only asynchronous methods, so embrace it and start making your method asynchronous as well.

关于第二个错误，原因是user manager没有FindById方法，而是仅仅有FindByIdAsync方法。你将在很多使用ASP.NET Core的地方看到，仅有异步方法，所以拥抱并开始使用异步方法吧。

In your case, you would need to change the Index method like this:

在你的情况下，你需要像这样变更Index方法：

// method is async and returns a Task
public async Task<IActionResult> Index()
{
    var userId = User.GetUserId();

    // call `FindByIdAsync` and await the result
    ApplicationUser user = await userManager.FindByIdAsync(userId);

    ViewBag.UserId = userId;
    ViewBag.DefaultListId = user.DefaultListId;

    return View();
}

As you can see, it does not require many changes to make the method asynchronous. Most of it stays just the same.

正如你看到的，使用异步方法不需要太多的变化，很多都是一样的。

原文链接