C#计时器的三种实现方法

public partial class Timer : Form
  {
    System.DateTime TimeNow = new DateTime();
    TimeSpan TimeCount = new TimeSpan();
    public Timer()
    {
      InitializeComponent();
    }
    private void btnTimeStart_Click(object sender, EventArgs e)
    {
      MyTimer.Start();
      TimeNow = DateTime.Now;
    }
    private void Timer_Load(object sender, EventArgs e)
    { 
      MyTimer.Interval = 1000;
    }
    private void btnTimeStop_Click(object sender, EventArgs e)
    {
      MyTimer.Stop();
    }
    private void MyTimer_Tick(object sender, EventArgs e)
    {
      TimeCount = DateTime.Now - TimeNow;
      txtTimeShow.Text = string.Format("{0:00}:{1:00}:{2:00}", TimeCount.Hours, TimeCount.Minutes, TimeCount.Seconds);
    }
    private void txtTimeShow_TextChanged(object sender, EventArgs e)
    {
    }
  }

public partial class Timer2 : Form
  {
    //定义Timer类变量
    System.Timers.Timer Mytimer;
    long TimeCount;
    //定义委托
    public delegate void SetControlValue(long value);
    public Timer2()
    {
      InitializeComponent();
    }
    private void label1_Click(object sender, EventArgs e)
    {
    }
    //开始计时
    private void btnTimeStart_Click(object sender, EventArgs e)
    {
      Mytimer.Start();
      TimeCount = 0;
    }
    //停止计时
    private void btnTimeStop_Click(object sender, EventArgs e)
    {
      Mytimer.Stop();
    }
    private void Timer2_Load(object sender, EventArgs e)
    {
      //设置时间间隔ms
      int interval = 1000; 
      Mytimer = new System.Timers.Timer(interval);
      //设置重复计时
      Mytimer.AutoReset = true;
      //设置执行System.Timers.Timer.Elapsed事件
      Mytimer.Elapsed += new System.Timers.ElapsedEventHandler(Mytimer_tick);
    }
    private void Mytimer_tick(object sender, System.Timers.ElapsedEventArgs e)
    { 
      this.Invoke(new SetControlValue(ShowTime), TimeCount);
      TimeCount++;
    }
    private void ShowTime(long t)
    {
      TimeSpan temp = new TimeSpan(0,0,(int)t);
      txtTimeShow.Text = string.Format("{0:00}:{1:00}:{2:00}", temp.Hours, temp.Minutes,temp.Seconds);
    }
    private void txtTimeShow_TextChanged(object sender, EventArgs e)
    {
    }  
  }

public partial class Timer2 : Form
  {
    System.Threading.Timer Mytimer;
    long TimeCount;
    delegate void SetValue();
    public Timer2()
    {
      InitializeComponent();
    }
    private void label1_Click(object sender, EventArgs e)
    {
    }
    private void TimerUp(object state)
    {      
      this.Invoke(new SetValue(ShowTime));
      TimeCount++;
    }
    public void ShowTime()
    {      
      TimeSpan t = new TimeSpan(0,0, (int)TimeCount);
      txtTimeShow.Text = string.Format("{0:00}:{1:00}:{2:00}",t.Hours,t.Minutes,t.Seconds);
    }
    //开始计时
    private void btnTimeStart_Click(object sender, EventArgs e)
    {
      TimeCount = 0;
      Mytimer.Change(0, 1000);      
    }
    //停止计时
    private void btnTimeStop_Click(object sender, EventArgs e)
    {
      Mytimer.Change(Timeout.Infinite, 1000);
    }
    private void Timer2_Load(object sender, EventArgs e)
    {
      Mytimer = new System.Threading.Timer(new TimerCallback(TimerUp), null, Timeout.Infinite, 1000);
    }
    private void txtTimeShow_TextChanged(object sender, EventArgs e)
    {
    }    
  }