关于LIST.Select（）.ToList()慢的问题

var sendlist = emailList.Select(email => new MailMessage {
                                                    MailServer = SMTPServer,
                                                    UserName = Sender,
                                                    PassWord = EmailPassword,
                                                    ServerCode = ServerCode,

                                                    ToAddr = email.Email,
                                                    BCC = string.Empty,
                                                    CC = string.Empty,

                                                    Title =Tittle,
                                                    Body = Content,
                                                    BodyText = Description,
                                                }).ToList();

代码如上，emailList是一个List<T>,有五万条记录，结果上面的代码运行居然要用到半小时才完成。经多次调试，的确是时间主要在Lambda表达式上。因为SMTPServer是一个全局变量，并非局总变量，每一行都要重新去获取。

只是一个全局变量就这么慢，那么如果是一个函数呢。

代码变成如下：

var mailServer = SMTPServer
var sendlist = emailList.Select(email => new MailMessage {
                                                    MailServer = mailServer,
                                                    UserName = Sender,
                                                    PassWord = EmailPassword,
                                                    ServerCode = ServerCode,

                                                    ToAddr = email.Email,
                                                    BCC = string.Empty,
                                                    CC = string.Empty,

                                                    Title =Tittle,
Body = ToContent(Content),
                                                    BodyText = Description,
                                                }).ToList();

结过测试，也当出现同样的情况。

为此，在写类似的代码时，不要出现全局变量和函数。

如果非要用到呢？

全局变量的解决方法：把全局变量的值赋给一个局部变量就行了。

如：

var mailServer = SMTPServer
var sendlist = emailList.Select(email => new MailMessage {
MailServer = mailServer,
                                                    UserName = Sender,
                                                    PassWord = EmailPassword,
                                                    ServerCode = ServerCode,

                                                    ToAddr = email.Email,
                                                    BCC = string.Empty,
                                                    CC = string.Empty,

                                                    Title =Tittle,
                                                    Body = Content,
                                                    BodyText = Description,
                                                }).ToList();

函数的方法，暂时没有想到别的方法，只能在修改业务了。

贴子链接http://bbs.csdn.net/topics/390500602