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用System.Timers类实现

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Timers;

namespace ConsoleApplication3
{
   class Program
   {
       static void Main(string[] args)
       {
           Timer t = new Timer();
           t.Elapsed += new ElapsedEventHandler(OnTimedEvent);
           t.Interval = 1000;
           t.Enabled = true;
           Console.Read();
       }

       private static void OnTimedEvent(object source, ElapsedEventArgs e)
       {
           Console.Clear();
           Console.WriteLine(DateTime.Now);
       }
   }
} 

运行效果：

用线程实现

TimerTest类：

class TimerTest
    {
        //线程名
        string _ThreadName;
        public string ThreadName
        {
            get { return _ThreadName; }
            private set { _ThreadName = value; }
        }

        //时间间隔
        int _TimeInterval;
        public int TimeInterval
        {
            get { return _TimeInterval; }
            set { _TimeInterval = value; }
        }

        //当前计时器是否启用 true：启用 false：不启用
        bool _Enabled;
        public bool Enabled
        {
            get { return _Enabled; }
            set { _Enabled = value; }
        }
        //每隔一段时间需要运行的事件
        public delegate void TickEventHandler();
        public event TickEventHandler TickEvent;
        /// <summary>
        /// 建立一个定时器
        /// </summary>
        /// <param name="ThreadName">线程名</param>
        /// <param name="TimeInterval">时间间隔</param>
        public TimerTest(string ThreadName,int TimeInterval = int.MaxValue)
        {
            this.ThreadName = ThreadName;
            this.TimeInterval = TimeInterval;
            this.Enabled = false;
        }

        /// <summary>
        /// 定期执行事件
        /// </summary>
        public void Run()
        {
            while (true)
            {
                //如果当前计时器并未启用，则每隔一段事件监测是否被启用
                if (!this.Enabled)
                {
                    Thread.Sleep(100);
                    continue;
                }
                //触发事件TickEvent
                if (TickEvent != null)
                {
                    TickEvent();
                }
                //休眠一定的事件，等待下一个循环
                Thread.Sleep(TimeInterval % 100);
                for (int temp = 0; temp < TimeInterval/100; temp++)
                {
                    Thread.Sleep(100);
                    if (!this.Enabled)
                    {
                        break;
                    }
                }
            }
        }
    }

调用程序：

 static void Main(string[] args)
        {           
            TimerTest tt = new TimerTest("timer_test",1000);
            tt.Enabled = true;
            tt.TickEvent += TestHandler;
            Thread timer = new Thread(tt.Run);
            timer.Start();
            Console.ReadKey();
        }

        static void TestHandler()
        {
            Console.WriteLine(DateTime.Now.ToLongTimeString());
        }

运行效果：