asp.net – ‘检测到Autofac循环组件依赖性’错误

我有以下两个班级：

public class UserService : IUserService
{
    private readonly IUserRepository _repo;
    private readonly IMailService _mailService;
    public UserService(IUserRepository repo,IMailService mailService)
    {
        _repo = repo;
        _mailService = mailService;
    }
}

public class MailService : IMailService
{
    private readonly IMailRepository _repo;
    private readonly IUserService _userService;
    public MailService(IMailRepository repo,IUserService userService)
    {
        _repo = repo;
        _userService = userService;
    }
}

最初,我的UserService类不需要MailService类的实例,但是现在它确实如此,并且自从将这个引入UserService构造函数以来已经出现了这个循环依赖性错误,并且作为一个新手,我不知道如何解决这个问题

这是我的课程目前在Autofac中注册的方式：

var builder = new ContainerBuilder();

// controllers                      
builder.RegisterControllers(Assembly.GetAssembly(typeof(UsersController)));

// register other classes
builder.RegisterType<UserRepository>().As<IUserRepository>();
builder.RegisterType<MailRepository>().As<IMailRepository>();
builder.RegisterType<UserService>().As<IUserService>();
builder.RegisterType<MailService>().As<IMailService>();