非同步寄Mail

非同步(Asynchronous)的設計方式。我在們程式結束前，常常沒有辦法確定所有的mail是否傳送完成。所以這個範例如使用ManualResetEvent類別，利用WaitOne()與Set()方法控制。等到所有的mail傳送完成才對離開foreach loop

using System.Net.Mail; 
using System.Threading; 

protected static void SendMail(IEnumerable<MailMessage> msgs, string smtp_host) 
{
	foreach (MailMessage msg in msgs)
	{
		SmtpClient smtp = new SmtpClient(smtp_host);
		smtp.SendCompleted += new SendCompletedEventHandler(SendCompletedCallback);
		ManualResetEvent wait = new ManualResetEvent(false);
		smtp.SendAsync(msg, new object[] {wait });
		wait.WaitOne();
	} 
} 
public static void SendCompletedCallback(object sender, AsyncCompletedEventArgs e) 
{
	object[] tokens = (object[])e.UserState;
	ManualResetEvent wait = (ManualResetEvent)tokens[0];
	wait.Set();
}