How to get current user in asp.net core

Question

I want to get the current user, so I can access fields like their email address. But I can't do that in asp.net core. This is my code:

HttpContext almost is null in constructor of controller. It's not good to get a user in each action. I want to get the user's information once and save it to ViewData;

public DashboardController()
{
    var user = HttpContext.User.GetUserId();
}

Answer 1

User.FindFirst(ClaimTypes.NameIdentifier).Value

EDIT for constructor

Below code works:

public Controller(IHttpContextAccessor httpContextAccessor)
{
    var userId = httpContextAccessor.HttpContext.User.FindFirst(ClaimTypes.NameIdentifier).Value 
}

Edit for RTM

You should register IHttpContextAccessor:

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddHttpContextAccessor();
    }