The following is snippets of my code:

public class OrganizationLayerDetail : CBase
{
//an interface
private static volatile IOrganizationLayerDetail iBuilder = null;

private OrganizationLayerDetail( object AppServer, string language ) : base( AppServer, language )
{
iBuilder = CDC.PowerHRP.DALFactory.OrganizationLayerDetail.Cr eate(AppServer,Language);
}

private static void creatIbuilder( object AppServer, string language )
{
if(iBuilder == null){
    lock(typeof(IOrganizationLayerDetail))
    {
        if(iBuilder == null)
        {
        new OrganizationLayerDetail(AppServer,language);
        }
    }
}
}


public static System.Data.DataRowCollection getDetail(string strCode, object AppServer, string language )
        {
            creatIbuilder(AppServer,language );
            System.Data.DataRowCollection dst = iBuilder.getDetail(strCode,AppServer,language);
            return dst;
        }

}


I invoke "getDetail(...)" in my web form, when i first invoke it ,of course iBuilder is null , but when i closed the application, and restarted the application, iBuilder isn't null,why?

Expect for someone to help me to understand this, and give me a solution for this, thanks first!

When you run code in a web application the code is executing inside the aspnet_wp process (wp stands for 'worker process'). Because this process doesn't close after a page request, all the classes that are loaded up for a page hit stay loaded. Things aren't unloaded until you restart IIS or somehow else recycle the .net worker process. Because of this, your static variable remains alive between page hits.

Yes ! :O), thank you very much!