.NET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 = "[email protected]";
                    string sender="test";
                    string mail_to = "[email protected]";
                    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);
        }

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