user_signed_in？在 ApplicationHelper 中定义的方法不可用于 AuthenticatedUser 。因为你可以从请求中获取会话，我只需直接在 AuthenticatedUser 中查看：

The user_signed_in? method defined in ApplicationHelper is not available to AuthenticatedUser. Since you can get the session from the request I would just check it directly in AuthenticatedUser:

class AuthenticatedUser
  def self.matches?(request)
    !!request.session[:user_id]
  end
end