C#由于循环依赖关系而在未引用的项目中调用方法

我有两个类的控制器和CountDownTimer。具有控制器的项目引用具有CountDownTimer类的项目。我在CountDownTimer类中有一些方法（TickUpdate），每当计时器倒计时一秒，它们就会调用控制器类中的方法。但由于循环依赖关系，我无法在CountDownTimer项目中引用控制器项目。

所以我的问题是，有没有办法从倒计时类中调用TickUpdate方法？

using SailTimerClassLibrary;
namespace SailTimerUIProject
{
    public class Controller : ApplicationContext
    {
    //Store a reference to the UI
    internal frmMain MainUI { get; set; }
    private int seconds = 30;
    CountDownTimer timer;
    public Controller()
    {
        MainUI = new frmMain(this);
        //We can do any necessary checks or changes to the MainUI here before it becomes visible
        MainUI.Show();
        timer = new CountDownTimer(seconds);
        TickUpdate(("" + seconds / 60).PadLeft(2, '0') + "m:" + ("" + seconds % 60).PadLeft(2, '0') + "s");
    }
    internal void TickUpdate(string mmss)
    {
        MainUI.lblTimer.Text = mmss;
    }
    internal void StartTimer()
    {
        timer.StartTimer();
    }
}
}

namespace SailTimerClassLibrary
{
public class CountDownTimer : ICountDownTimer
{
    private int seconds; // Time in seconds
    private int reSetValue; // Time in seconds
    public System.Windows.Forms.Timer timer1;
    public CountDownTimer(int seconds)
    {
        this.seconds = seconds;
        reSetValue = seconds;
        timer1 = new System.Windows.Forms.Timer();
        timer1.Tick += new EventHandler(timer1_Tick); // Add Handler(timer1_Tick)
        timer1.Interval = 1000; // 1 second
        //TickUpdate(("" + seconds / 60).PadLeft(2, '0') + "m:" + ("" + seconds % 60).PadLeft(2, '0') + "s");
    }
    public void timer1_Tick(object sender, EventArgs e)
    {
        seconds--; // Decrement seconds
        if (seconds == 0) // Stop Timer at 0
        {
            timer1.Stop(); // Stop timer
        }
        else
        {
            //TickUpdate(convertSecondToMMSS());
            if (seconds % 60 == 0 || seconds >= 1 && seconds <= 10)
            {
                //TickUpdate(seconds);
            }
        }
    }
    public void StartTimer()
    {
        timer1.Start(); // Start Timer
    }
    public string convertSecondToMMSS()
    {
        TimeSpan t = TimeSpan.FromSeconds(seconds);
        string str = string.Format("{0:D2}m:{1:D2}s", //{0:D2}h:{1:D2}m:{2:D2}s:{3:D3}ms
            t.Minutes,
            t.Seconds);
        return str;
    }
    public void StopTimer()
    {
        timer1.Stop();
    }
    public void ResetTimer()
    {
        timer1.Stop();
        seconds = reSetValue;
        //parent.TickUpdate(convertSecondToMMSS());
    }
    public void SetTimer(int seconds)
    {
        timer1.Stop();
        this.seconds = seconds;
        reSetValue = seconds;
        //parent.TickUpdate(convertSecondToMMSS());
    }
}
}