功能

倒计时结束时触发相应事件。
倒计时期间，每隔一段时间，发出事件告知外界多久后倒计时结束。
倒计时期间（未结束前），可暂停、继续、重新开始倒计时。

代码

CountDownTimer.cs

using System;
using System.Collections;
using UnityEngine;

public class CountDownTimer
{
    private float _durationSeconds;
    private float _intervalSeconds;
    private float _remainSeconds;
    private bool _isRuning;
    private IEnumerator _countDownCoroutine;
    // 剩余时长，总时长
    public event Action<float, float> TellRemainSecondsEvent;
    private Action _endAction;

    public CountDownTimer(float durationSeconds, Action endAction, float intervalSeconds = 1f, bool shouldInstantlyStart = true)
    {
        _durationSeconds = durationSeconds;
        _endAction = endAction;
        _intervalSeconds = intervalSeconds;
        if (shouldInstantlyStart)
        {
            Start();
        }
    }
    public void MyDestroy()
    {
        StopCountDown();
        _endAction = null;
    }

    public void Start()
    {
        StopCountDown();
        ResetRemainSeonds();
        Continue();
        StartCountDown();
    }

    public void Pause()
    {
        _isRuning = false;
    }
    public void Continue()
    {
        _isRuning = true;
    }
    public void Restart()
    {
        if (_countDownCoroutine == null)
        {
            Debug.Log("倒计时已结束，无法重新开始！");
        }
        else
        {
            ResetRemainSeonds();
            Continue();
        }
    }
    public void Cancel()
    {
        MyDestroy();
    }

    private void ResetRemainSeonds()
    {
        _remainSeconds = _durationSeconds;
    }

    private void StartCountDown()
    {
        _countDownCoroutine = CountDownCoroutine();
        MonoSys.Instance.StartCoroutine(_countDownCoroutine);

        IEnumerator CountDownCoroutine()
        {
            var waitForSeconds = new WaitForSeconds(_intervalSeconds);
            TellRemainSecondsEvent?.Invoke(_remainSeconds, _durationSeconds);
            while (true)
            {
                yield return waitForSeconds;
                if (_isRuning)
                {
                    _remainSeconds -= _intervalSeconds;
                    if (_remainSeconds < 0)
                    {
                        _remainSeconds = 0;
                    }
                    TellRemainSecondsEvent?.Invoke(_remainSeconds, _durationSeconds);
                    if (_remainSeconds == 0)
                    {
                        _endAction?.Invoke();
                        break;
                    }
                }
            }
            MyDestroy();
        }
    }
    private void StopCountDown()
    {
        MonoSys.Instance.DestroyCoroutine(ref _countDownCoroutine);
    }
}