我试图将服务注入到动作过滤器中，但是没有将所需的服务注入构造函数中。这是我所拥有的：

public class EnsureUserLoggedIn : ActionFilterAttribute
{
    private readonly ISessionService _sessionService;

    public EnsureUserLoggedIn()
    {
        // I was unable able to remove the default ctor 
        // because of compilation error while using the 
        // attribute in my controller
    }

    public EnsureUserLoggedIn(ISessionService sessionService)
    {
        _sessionService = sessionService;
    }

    public override void OnActionExecuting(ActionExecutingContext context)
    {
        // Problem: _sessionService is null here
        if (_sessionService.LoggedInUser == null)
        {
            context.HttpContext.Response.StatusCode = (int)HttpStatusCode.Unauthorized;
            context.Result = new JsonResult("Unauthorized");
        }
    }
}

我像这样装饰控制器：

[Route("api/issues"), EnsureUserLoggedIn]
public class IssueController : Controller
{
}

启动文件

services.AddScoped<ISessionService, SessionService>();