A System.Web.Security.MembershipUser object representing the specified user. If the username parameter does not correspond to an existing user, this method returns null.
The Membership.GetUser(string) method retrieves the user information from the data source and creates a System.Web.Security.MembershipUser object populated with the returned data. If you use one of the Membership.GetUser overloads that does not take a username parameter, Membership.GetUser returns the information for the current logged-on membership user. The current logged-on membership user is identified by the System.Security.Principal.IIdentity.Name of the user in the current System.Web.HttpContext.
You can also specify whether you want Membership.GetUser to update the last-activity date/time stamp for the user being retrieved with the userIsOnline parameter. Of the erload:System.Web.Security.Membership.GetUser overloads that do not take a userIsOnline parameter, Membership.GetUser implicitly updates the last-activity date/time stamp for the user. Membership.GetUser(string) and Membership.GetUser(object) do not.