/// <summary>
/// Track the page of results requested
/// </summary>
private static int _gPage = 1;
public static int gPage
{
	get { return _gPage; }
	set { _gPage = value; }
}
/// <summary>
/// Track the group requested; if this changes then the gPage should be reset
/// </summary>
private static string _gGroup = String.Empty;
public static string gGroup
{
	get { return _gGroup; }
	set { _gGroup = value; }
}

var rResultsLimit = 20; /* Only return 20 members at a time */
var gDomain = "LDAP://your.ad.domain"; /* Domain to query */
var gSize = 1000; /* The maximum number of members in the AD group; this may be superceded by a size setting in DirectoryServices or the Domain */
var currentGroup = "ADGroupName"; /* Name of the AD group to get members from */
/* If the current group requested is not what may have already been requested, set to the current group and update page number */
if (gGroup.ToLower().Trim() != currentGroup.ToLower().Trim()) {
	gPage = 1;
	gGroup = currentGroup;
}
var result = customADInterface.retrieveADGroupMembershipAndUserDetail(rResultsLimit, gDomain, gGroup, gSize, gPage);
if (result.ToLower() == "completed") {
	/* Increment page number in preparation for getting the next page of results */
	gPage++;
}
else if (result.ToLower() == "lastpage") {
	/* The last page of results has been reached, so there is no need in getting another page of results */
}
else if (result.ToLower() == "nodata") {
	/* Nothing was found; perhaps the name of the AD group was not correct... */
}

public class customADInterface
{
	/// <summary>
	/// Instantiate the DataSet; will contain the DataTable of data
	/// </summary>
	public static System.Data.DataSet dataSetContainer = new DataSet();
	/// <summary>
	/// Store the actual number of members in the Group up to the maximum allowed
	/// </summary>
	private static int _countDomainGroupMembers = 0;
	public static int countDomainGroupMembers
	{
		get { return _countDomainGroupMembers; }
		set { _countDomainGroupMembers = value; }
	}
	/// <summary>
	/// Store the AD path of the AD Group
	/// </summary>
	private static string _fullADGroupPath = String.Empty;
	public static string fullADGroupPath
	{
		get { return _fullADGroupPath; }
		set { _fullADGroupPath = value; }
	}
	/// <summary>
	/// This performs the high level orchestration to retrieve the members of an AD group and various attributes, along with pagination.
	/// </summary>
	/// <param name="rLimit">20 - maximum number of members to retrieve</param>
	/// <param name="tDomain">LDAP://your.ad.domain</param>
	/// <param name="tGroup">DomainAdmins - name of AD group to get the members of</param>
	/// <param name="tGroupSizeLimit">1000 - maximum size of the AD group; the actual number of members may be less than this number so needing a specific number is not required as it will be determined</param>
	/// <param name="rCurrentPage">1 - the current page of members to retrieve</param>
	/// <returns>string - completed = data was found, nodata = no data was found, lastpage = last page of data found</returns>
	public static string retrieveADGroupMembershipAndUserDetails(int rLimit, string tDomain, string tGroup, int tGroupSizeLimit, int rCurrentPage)
	{
		/* Get arguments */
		var rResultsLimit = rLimit;
		var gDomain = tDomain;
		var gGroup = tGroup;
		var gGroupSizeLimit = tGroupSizeLimit;
		var rCurrentPageResults = rCurrentPage;
		var results = "nodata";
		/* Create DataTable and Column Names */
		System.Data.DataTable table = new DataTable();
		DataColumn column;
		DataRow row;

		column = new DataColumn();
		column.DataType = System.Type.GetType("System.String");
		column.ColumnName = "CN";
		column.ReadOnly = true;
		column.Unique = false;
		table.Columns.Add(column);

		// Clear any pre-existing content for the current iteration
		dataSetContainer.Tables.Clear();

		// Add the new DataTable to the DataSetContainer
		dataSetContainer.Tables.Add(table);

		// STEP 1: Get group path information and count of members in the group only if we do not already have that information; the initial query will be slower than follow-up queries.
		if (rCurrentPageResults == 1) {
			// Get the full AD path of the group in the domain
			DirectoryEntry rootEntry = new DirectoryEntry(gDomain);
			DirectorySearcher searcher = new DirectorySearcher(rootEntry);
			searcher.Filter = "(&(ObjectClass=Group)(CN=" + gGroup + "))";
			SearchResult rawADGroupPath = searcher.FindOne();
			fullADGroupPath = rawADGroupPath.Path.ToString().Replace(gDomain + "/", "");

			// Get count of members in the group
			searcher.Filter = "(&(ObjectClass=person)(memberOf=" + fullADGroupPath + "))";
			/* Attempting searcher.VirtualListView.ApproximateTotal did not return what was expected so loop instead */
			searcher.PropertiesToLoad.Add("cn");
			/* Sort is required or DirectoryVirtualListView will not work */
			searcher.Sort = new SortOption("cn", SortDirection.Ascending);
			searcher.VirtualListView = new DirectoryVirtualListView(0, gGroupSizeLimit, 1);
			SearchResultCollection tmpData = searcher.FindAll();
			foreach (SearchResult step in tmpData) { countDomainGroupMembers++; }
		}
		// STEP 2: Get the members in the AD group in paginated form
		var beforeCountPosition = 0;
		var afterCountPosition = countDomainGroupMembers;
		var startOffsetPosition = 0;
		// Determine the block of members to return from the AD group
		if (rCurrentPageResults == 1) { startOffsetPosition = 1; }
		else {
			startOffsetPosition = (rResultsLimit * (rCurrentPageResults - 1)) + 1;
		}
		afterCountPosition = rResultsLimit - 1;
		// Determine whether to get results or not
		var resultsLastPageReached = 0;
		if (startOffsetPosition < countDomainGroupMembers) {
			// Determine if this is the last set of results to retrieve
			if ((countDomainGroupMembers - (startOffsetPosition + afterCountPosition)) <= 0) { resultsLastPageReached = 1; }
			// Get results for this iteration
			var tmpFoundData = 0;
			DirectoryEntry rootEntryMembers = new DirectoryEntry(gDomain);
			DirectorySearcher memberRetrieve = new DirectorySearcher(rootEntryMembers);
			memberRetrieve.Filter = "(&(ObjectClass=person)(memberOf=" + fullADGroupPath + "))";
			memberRetrieve.PropertiesToLoad.Add("cn");
			memberRetrieve.Sort = new SortOption("cn", SortDirection.Ascending);
			memberRetrieve.VirtualListView = new DirectoryVirtualListView(beforeCountPosition, afterCountPosition, startOffsetPosition);
			SearchResultCollection memberData = memberRetrieve.FindAll();
			foreach (SearchResult entry in memberData)
			{
				var e_cn = "";
				try { e_cn = entry.Properties["cn"][0].ToString(); }
				catch (Exception e) { /* No data present */ }
				// Save result to DataRow object
				row = table.NewRow();
				row["CN"] = e_cn;
				table.Rows.Add(row);
				tmpFoundData = 1;
			}
			if (tmpFoundData == 1) {
				if (resultsLastPageReached == 1) { results = "lastpage"; }
				else { results = "completed"; }
			}
			else {
				if (resultsLastPageReached == 1) { results = "lastpage"; }
				else { results = "nodata"; }
			}
		}
		else {
			// Limit reached, no results left to retrieve
			results = "nodata";
		}
		return results;
	}
}