How to determine whether a user is a member of the ad domain

How can I determine whether a user belongs to a member in a domain group? I checked a lot of information and shared the information below.

Userisgroupmember (userlogin, rolename) is used to determine whether a user is a domain member.
Note: Because domain groups are nested in other domain groups, traversal is required.

Code
Private   Static   String Adpath =   " LDAP: // domain " ;

/**/ ///   <Summary>
/// Determine whether a user is a domain member
///   </Summary>
///   <Param name = "userlogin"> User Name </Param>
///   <Param name = "rolename"> Domain group name </Param>
///   <Returns> </returns>
Private   Static   Bool Userisgroupmember ( String Userlogin, String Rolename)
{
Directoryentry entry =   New Directoryentry (adpath );
Directorysearcher mysearcher =   New Directorysearcher (entry );

Mysearcher. Filter =   String . Format ( " (& (Objectclass = user) (samaccountname = {0 })) " , Userlogin );
Mysearcher. propertiestoload. Add ( " Memberof " );
Searchresult mysr = Mysearcher. findone ();

If (Mysr. properties. Count >   1 ) // Two attributes are returned, one is the built-in adspath, and the other is the propertiestoload loaded
{
String [] Memberof =   New   String [Mysr. properties [ " Memberof " ]. Count];
Int I =   0 ;
Foreach (Object mycoll In Mysr. properties [ " Memberof " ])
{
Memberof [I] = Mycoll. tostring (). substring ( 3 , Mycoll. tostring (). indexof ( " , " ) -   3 );
If (Memberof [I] = Rolename)
Return   True ;
I ++ ;
}
// In fact, this layer of loop is a breadth-first algorithm, because considering that a person directly belongs to a security group is more likely, this is more efficient. if the following loop is placed in the IF esle above, the depth is given priority.
Foreach ( String Groupname In Memberof)
{
If(Memberisgroupmember (groupname, rolename ))
Return True;
}
}
Return   False ;
}

Private   Static   Bool Memberisgroupmember ( String Groupname, String Rolename)
{
Bool Isfind =   False ;
Directoryentry entry =   New Directoryentry (adpath );
Directorysearcher mysearcher =   New Directorysearcher (entry );
Mysearcher. Filter =   String . Format ( " (& (Objectclass = Group) (CN = {0 })) " , Groupname );
Mysearcher. propertiestoload. Add ( " Memberof " );
Searchresult mysr = Mysearcher. findone ();
String Memberof;
Try
{
If (Mysr. properties. Count >   1 ) // Two attributes are returned, one is the built-in adspath, and the other is the propertiestoload loaded
{
Foreach (Object mycoll In Mysr. properties [ " Memberof " ])
{
Memberof = Mycoll. tostring (). substring ( 3 , Mycoll. tostring (). indexof ( " , " ) -   3 );
If (Memberof = Rolename)
{< br> isfind = true ;< br> Break ;< BR >}
Else   If (Memberisgroupmember (memberof, rolename ))
{< br> isfind = true ;< br> Break ;< BR >}
}
}
}
Catch (Exception ex)
{}
Return Isfind;
}

References:
Http://www.cnblogs.com/zyk/archive/2004/11/02/59707.html