使用System.Timers.Timer类实现程序定时执行

     在C#里关于定时器类有3个：System.Windows.Forms.Timer类、System.Threading.Timer类和System.Timers.Timer类。

     System.Windows.Forms.Timer是应用于WinForm中的，它是通过Windows消息机制实现的，类似于VB或Delphi中的Timer控件，内部使用API  SetTimer实现的。它的主要缺点是计时不精确，而且必须有消息循环，Console  Application(控制台应用程序)无法使用。

      System.Timers.Timer和System.Threading.Timer非常类似，它们是通过.NET Thread Pool实现轻量、精确的计时，对应用程序、消息没有特别的要求。System.Timers.Timer还可以应用于WinForm，完全取代上面的Timer控件。它们的缺点是不支持直接的拖放，需要手工编码。

         public   int  wrong  =   0 ;
        System.Timers.Timer time  =   new  System.Timers.Timer();
        
         private   void  begin_Click( object  sender, EventArgs e)
        {
             if  (action.Text  ==   " 启动监测 " )
            {
                action.Text  =   " 停止监测 " ;
                label2.Text  =   " 已启动 " ;

                 if  (time.Interval.ToString()  ==   " 100 " )  //  The default value of interval is 100s.
                {
                    time.Elapsed  +=   new  ElapsedEventHandler(TimeEvent);
                    time.Interval  =   1000 ;
                }
                time.Enabled  =   true ;
            }
             else
            {
                action.Text  =   " 启动监测 " ;
                label2.Text  =   " 已停止 " ;

                time.Enabled  =   false ;
            }

        }

         private   static   void  TimeEvent( object  source, ElapsedEventArgs e)
        {
             int  tsec  =  e.SignalTime.Second;
             int  isec  =   10 ;
             if  (tsec  ==  isec)  // it will be activated at 10s of every minutes.
            {
                 if  ( ! Check( " http://www.test.com " ))
                {
                     string  smtp_server = " 192.168.8.1 " ;
                     int  port  =   25 ;
                     string  mail_from  =   " [e-mail] " ;
                     string  sender = " test " ;
                     string  mail_to  =   " [e-mail] " ;
                     string  receiver = " adminer " ;
                     string  subject  =   " The site is run out exception on  "   +  DateTime.Now.ToString( " yyyyMMddhhmmss " );
                     string  body  =   " The site can not open on  "   +  DateTime.Now.ToString()  +   " ,please check it ! " ;
                     try
                    {
                        SendEmail(smtp_server, port, mail_from, sender, mail_to, receiver, subject, body);
                    }
                     catch (Exception ex)
                    {
                        MessageBox.Show(ex.Message);
                    }
                }
            }
        }

         private   static   bool  Check( string  urlStr)
        {
            HttpWebRequest myWebRequest  =   null ;
             try
            {
                myWebRequest  =  (HttpWebRequest)WebRequest.Create(urlStr);
                HttpWebResponse res  =  (HttpWebResponse)myWebRequest.GetResponse();
                 if  (res.StatusCode  ==  HttpStatusCode.OK)
                {
                    res.Close();
                     return   true ;
                }
                 else
                {
                    res.Close();
                     return   false ;
                }
            }
             catch  (Exception)
            {
                 return   false ;
            }
        }

         public   static   void  SendEmail( string  smtp_server,  int  port,  string  mail_from,  string  sender,  string  mail_to,  string  receiver,  string  subject,  string  body)
        {
            MailAddress from  =   new  MailAddress(mail_from, sender);
            MailAddress to  =   new  MailAddress(mail_to, receiver);
            MailMessage message  =   new  MailMessage(from, to);
            message.BodyEncoding  =  Encoding.UTF8;
            message.IsBodyHtml  =   true ;
            message.Subject  =  subject;
            message.Body  =  body;

            SmtpClient client  =   new  SmtpClient(smtp_server, port);
             // SmtpClient client = new SmtpClient(smtp_server);

             //  Add credentials if the SMTP server requires them. 
            client.Credentials  =  CredentialCache.DefaultNetworkCredentials;
            client.Send(message);
        }