Querying Active Directory using .NET classes and LDAP queries

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.DirectoryServices;
using System.IO;

namespace ActiveDirQuery
{
	/// <summary>
	/// Summary description for ADQForm.
	/// </summary>
	public class ADQForm : Form
	{
		private TreeView	ObjectView; // the tree view on the main form
		private GroupBox	groupBox1;
		private CheckBox	UsersCB, ComputersCB, PrintersCB;
		private Label		FilterLabel1, FilterLabel2, FilterLabel3;
		private ImageList	myImageList; // image list for the tree view

		// query filters for fetching the objects
		private TextBox		UsersFilter, ComputersFilter, PrintersFilter;

		// state of the query
		public bool Querying = false;

		// basic nodes for the tree view
		private TreeNode RootNode; // this node should show the domain server name
		private TreeNode UsersNode, ComputersNode, PrintersNode;
		private Button QueryButton;
		private Button ExitButton;
		private GroupBox groupBox2;
		private Label label1;
		private Label label2;
		private Label label3;
		private Label label4;
		private GroupBox groupBox3;
		private Label label5;
		private Label label6;
		private Label label7;
		private TextBox PageTimeLimit;
		private TextBox TotalTimeLimit;
		private TextBox ObjsPerPage;
		private TextBox ObjsToFetch;
		private ComboBox searchOptionCB;
		private CheckBox SortResultsCB;
		private CheckBox CacheResultsCB;
		private Label label8;

		/// <summary>
		/// Required designer variable.
		/// </summary>
		private Container components = null;

		public ADQForm()
		{
			InitializeComponent();
			searchOptionCB.SelectedIndex = 0;

			// load images from the icon files
			myImageList = new ImageList();
			myImageList.Images.Add(new Icon("button.ico"));
			myImageList.Images.Add(new Icon("domain.ico"));
			myImageList.Images.Add(new Icon("computer.ico"));
			myImageList.Images.Add(new Icon("users.ico"));
			myImageList.Images.Add(new Icon("printer.ico"));

			// assign the imagelist to the tree view
			ObjectView.ImageList = myImageList;
			// prepare the root node
			GetRootNode();

			ComputersNode = new TreeNode("Computers", 2, 2);
			UsersNode = new TreeNode("Users", 3, 3);
			PrintersNode = new TreeNode("Printers", 4, 4);
		}

		/// <summary>
		/// Clean up any resources being used.
		/// </summary>
		protected override void Dispose( bool disposing )
		{
			if( disposing )
			{
				if (components != null) 
				{
					components.Dispose();
				}
			}
			base.Dispose( disposing );
		}

		#region Windows Form Designer generated code
		/// <summary>
		/// Required method for Designer support - do not modify
		/// the contents of this method with the code editor.
		/// </summary>
		private void InitializeComponent()
		{
			System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(ADQForm));
			this.ObjectView = new TreeView();
			this.groupBox1 = new GroupBox();
			this.FilterLabel3 = new Label();
			this.FilterLabel2 = new Label();
			this.FilterLabel1 = new Label();
			this.PrintersCB = new CheckBox();
			this.ComputersCB = new CheckBox();
			this.UsersCB = new CheckBox();
			this.UsersFilter = new TextBox();
			this.ComputersFilter = new TextBox();
			this.PrintersFilter = new TextBox();
			this.ExitButton = new Button();
			this.QueryButton = new Button();
			this.groupBox2 = new GroupBox();
			this.label3 = new Label();
			this.PageTimeLimit = new TextBox();
			this.label2 = new Label();
			this.ObjsPerPage = new TextBox();
			this.label1 = new Label();
			this.searchOptionCB = new ComboBox();
			this.label4 = new Label();
			this.groupBox3 = new GroupBox();
			this.TotalTimeLimit = new TextBox();
			this.label6 = new Label();
			this.label5 = new Label();
			this.ObjsToFetch = new TextBox();
			this.label7 = new Label();
			this.SortResultsCB = new CheckBox();
			this.CacheResultsCB = new CheckBox();
			this.label8 = new Label();
			this.groupBox1.SuspendLayout();
			this.groupBox2.SuspendLayout();
			this.groupBox3.SuspendLayout();
			this.SuspendLayout();
			// 
			// ObjectView
			// 
			this.ObjectView.Dock = DockStyle.Bottom;
			this.ObjectView.ImageIndex = -1;
			this.ObjectView.Location = new System.Drawing.Point(0, 264);
			this.ObjectView.Name = "ObjectView";
			this.ObjectView.SelectedImageIndex = -1;
			this.ObjectView.Size = new System.Drawing.Size(458, 261);
			this.ObjectView.TabIndex = 0;
			// 
			// groupBox1
			// 
			this.groupBox1.Controls.Add(this.FilterLabel3);
			this.groupBox1.Controls.Add(this.FilterLabel2);
			this.groupBox1.Controls.Add(this.FilterLabel1);
			this.groupBox1.Controls.Add(this.PrintersCB);
			this.groupBox1.Controls.Add(this.ComputersCB);
			this.groupBox1.Controls.Add(this.UsersCB);
			this.groupBox1.Controls.Add(this.UsersFilter);
			this.groupBox1.Controls.Add(this.ComputersFilter);
			this.groupBox1.Controls.Add(this.PrintersFilter);
			this.groupBox1.Location = new System.Drawing.Point(10, 8);
			this.groupBox1.Name = "groupBox1";
			this.groupBox1.Size = new System.Drawing.Size(330, 102);
			this.groupBox1.TabIndex = 1;
			this.groupBox1.TabStop = false;
			this.groupBox1.Text = "Objects to query";
			// 
			// FilterLabel3
			// 
			this.FilterLabel3.Enabled = false;
			this.FilterLabel3.Location = new System.Drawing.Point(86, 80);
			this.FilterLabel3.Name = "FilterLabel3";
			this.FilterLabel3.Size = new System.Drawing.Size(70, 18);
			this.FilterLabel3.TabIndex = 5;
			this.FilterLabel3.Text = "Name Filter :";
			// 
			// FilterLabel2
			// 
			this.FilterLabel2.Enabled = false;
			this.FilterLabel2.Location = new System.Drawing.Point(86, 50);
			this.FilterLabel2.Name = "FilterLabel2";
			this.FilterLabel2.Size = new System.Drawing.Size(70, 18);
			this.FilterLabel2.TabIndex = 4;
			this.FilterLabel2.Text = "Name Filter :";
			// 
			// FilterLabel1
			// 
			this.FilterLabel1.Enabled = false;
			this.FilterLabel1.Location = new System.Drawing.Point(86, 22);
			this.FilterLabel1.Name = "FilterLabel1";
			this.FilterLabel1.Size = new System.Drawing.Size(70, 18);
			this.FilterLabel1.TabIndex = 3;
			this.FilterLabel1.Text = "Name Filter :";
			// 
			// PrintersCB
			// 
			this.PrintersCB.Location = new System.Drawing.Point(8, 76);
			this.PrintersCB.Name = "PrintersCB";
			this.PrintersCB.Size = new System.Drawing.Size(80, 24);
			this.PrintersCB.TabIndex = 2;
			this.PrintersCB.Text = "Printers";
			this.PrintersCB.CheckedChanged += new EventHandler(this.OnPrintersCheckedChanged);
			// 
			// ComputersCB
			// 
			this.ComputersCB.Location = new System.Drawing.Point(8, 48);
			this.ComputersCB.Name = "ComputersCB";
			this.ComputersCB.Size = new System.Drawing.Size(80, 24);
			this.ComputersCB.TabIndex = 1;
			this.ComputersCB.Text = "Computers";
			this.ComputersCB.CheckedChanged += new EventHandler(this.OnComputersCheckedChanged);
			// 
			// UsersCB
			// 
			this.UsersCB.Location = new System.Drawing.Point(8, 20);
			this.UsersCB.Name = "UsersCB";
			this.UsersCB.Size = new System.Drawing.Size(80, 24);
			this.UsersCB.TabIndex = 0;
			this.UsersCB.Text = "Users";
			this.UsersCB.CheckedChanged += new EventHandler(this.OnUsersCheckedChanged);
			// 
			// UsersFilter
			// 
			this.UsersFilter.Enabled = false;
			this.UsersFilter.Location = new System.Drawing.Point(160, 22);
			this.UsersFilter.Name = "UsersFilter";
			this.UsersFilter.Size = new System.Drawing.Size(162, 20);
			this.UsersFilter.TabIndex = 6;
			this.UsersFilter.Text = "*";
			// 
			// ComputersFilter
			// 
			this.ComputersFilter.Enabled = false;
			this.ComputersFilter.Location = new System.Drawing.Point(160, 48);
			this.ComputersFilter.Name = "ComputersFilter";
			this.ComputersFilter.Size = new System.Drawing.Size(162, 20);
			this.ComputersFilter.TabIndex = 7;
			this.ComputersFilter.Text = "*";
			// 
			// PrintersFilter
			// 
			this.PrintersFilter.Enabled = false;
			this.PrintersFilter.Location = new System.Drawing.Point(160, 78);
			this.PrintersFilter.Name = "PrintersFilter";
			this.PrintersFilter.Size = new System.Drawing.Size(162, 20);
			this.PrintersFilter.TabIndex = 8;
			this.PrintersFilter.Text = "*";
			// 
			// ExitButton
			// 
			this.ExitButton.BackColor = Color.NavajoWhite;
			this.ExitButton.Location = new System.Drawing.Point(358, 76);
			this.ExitButton.Name = "ExitButton";
			this.ExitButton.Size = new System.Drawing.Size(88, 23);
			this.ExitButton.TabIndex = 10;
			this.ExitButton.Text = "Exit";
			this.ExitButton.Click += new System.EventHandler(this.OnExit);
			// 
			// QueryButton
			// 
			this.QueryButton.BackColor = Color.LightGreen;
			this.QueryButton.Image = ((System.Drawing.Image)(resources.GetObject("QueryButton.Image")));
			this.QueryButton.ImageAlign = System.Drawing.ContentAlignment.TopCenter;
			this.QueryButton.Location = new System.Drawing.Point(356, 14);
			this.QueryButton.Name = "QueryButton";
			this.QueryButton.Size = new System.Drawing.Size(88, 42);
			this.QueryButton.TabIndex = 9;
			this.QueryButton.Text = "Query";
			this.QueryButton.TextAlign = System.Drawing.ContentAlignment.BottomCenter;
			this.QueryButton.Click += new System.EventHandler(this.OnQuery);
			// 
			// groupBox2
			// 
			this.groupBox2.Controls.Add(this.label3);
			this.groupBox2.Controls.Add(this.PageTimeLimit);
			this.groupBox2.Controls.Add(this.label2);
			this.groupBox2.Controls.Add(this.ObjsPerPage);
			this.groupBox2.Controls.Add(this.label1);
			this.groupBox2.Location = new System.Drawing.Point(10, 120);
			this.groupBox2.Name = "groupBox2";
			this.groupBox2.Size = new System.Drawing.Size(212, 82);
			this.groupBox2.TabIndex = 11;
			this.groupBox2.TabStop = false;
			this.groupBox2.Text = "Page level options";
			// 
			// label3
			// 
			this.label3.Location = new System.Drawing.Point(176, 54);
			this.label3.Name = "label3";
			this.label3.Size = new System.Drawing.Size(28, 14);
			this.label3.TabIndex = 4;
			this.label3.Text = "secs";
			// 
			// PageTimeLimit
			// 
			this.PageTimeLimit.Location = new System.Drawing.Point(124, 50);
			this.PageTimeLimit.Name = "PageTimeLimit";
			this.PageTimeLimit.Size = new System.Drawing.Size(48, 20);
			this.PageTimeLimit.TabIndex = 3;
			this.PageTimeLimit.Text = "";
			this.PageTimeLimit.Validating += new CancelEventHandler(this.OnValidatingText);
			// 
			// label2
			// 
			this.label2.Location = new System.Drawing.Point(6, 52);
			this.label2.Name = "label2";
			this.label2.Size = new System.Drawing.Size(120, 16);
			this.label2.TabIndex = 2;
			this.label2.Text = "Per page time limit :";
			this.label2.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
			// 
			// ObjsPerPage
			// 
			this.ObjsPerPage.Location = new System.Drawing.Point(124, 24);
			this.ObjsPerPage.Name = "ObjsPerPage";
			this.ObjsPerPage.Size = new System.Drawing.Size(48, 20);
			this.ObjsPerPage.TabIndex = 1;
			this.ObjsPerPage.Text = "";
			this.ObjsPerPage.Validating += new CancelEventHandler(this.OnValidatingText);
			// 
			// label1
			// 
			this.label1.Location = new System.Drawing.Point(8, 26);
			this.label1.Name = "label1";
			this.label1.Size = new System.Drawing.Size(118, 16);
			this.label1.TabIndex = 0;
			this.label1.Text = "Max objects per page :";
			this.label1.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
			// 
			// searchOptionCB
			// 
			this.searchOptionCB.DropDownStyle = ComboBoxStyle.DropDownList;
			this.searchOptionCB.Items.AddRange(new object[] {
																"Search the complete sub tree",
																"Search only immediate children"});
			this.searchOptionCB.Location = new System.Drawing.Point(92, 210);
			this.searchOptionCB.Name = "searchOptionCB";
			this.searchOptionCB.Size = new System.Drawing.Size(176, 21);
			this.searchOptionCB.TabIndex = 12;
			// 
			// label4
			// 
			this.label4.Location = new System.Drawing.Point(12, 214);
			this.label4.Name = "label4";
			this.label4.Size = new System.Drawing.Size(80, 14);
			this.label4.TabIndex = 13;
			this.label4.Text = "Search option :";
			// 
			// groupBox3
			// 
			this.groupBox3.Controls.Add(this.TotalTimeLimit);
			this.groupBox3.Controls.Add(this.label6);
			this.groupBox3.Controls.Add(this.label5);
			this.groupBox3.Controls.Add(this.ObjsToFetch);
			this.groupBox3.Controls.Add(this.label7);
			this.groupBox3.Location = new System.Drawing.Point(226, 120);
			this.groupBox3.Name = "groupBox3";
			this.groupBox3.Size = new System.Drawing.Size(222, 84);
			this.groupBox3.TabIndex = 14;
			this.groupBox3.TabStop = false;
			this.groupBox3.Text = "Server level options";
			// 
			// TotalTimeLimit
			// 
			this.TotalTimeLimit.Location = new System.Drawing.Point(128, 50);
			this.TotalTimeLimit.Name = "TotalTimeLimit";
			this.TotalTimeLimit.Size = new System.Drawing.Size(48, 20);
			this.TotalTimeLimit.TabIndex = 7;
			this.TotalTimeLimit.Text = "";
			this.TotalTimeLimit.Validating += new CancelEventHandler(this.OnValidatingText);
			// 
			// label6
			// 
			this.label6.Location = new System.Drawing.Point(14, 52);
			this.label6.Name = "label6";
			this.label6.Size = new System.Drawing.Size(112, 16);
			this.label6.TabIndex = 6;
			this.label6.Text = "Total time limit :";
			this.label6.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
			// 
			// label5
			// 
			this.label5.Location = new System.Drawing.Point(14, 26);
			this.label5.Name = "label5";
			this.label5.Size = new System.Drawing.Size(112, 16);
			this.label5.TabIndex = 0;
			this.label5.Text = "Max objects to fetch :";
			this.label5.TextAlign = System.Drawing.ContentAlignment.MiddleRight;
			// 
			// ObjsToFetch
			// 
			this.ObjsToFetch.Location = new System.Drawing.Point(128, 24);
			this.ObjsToFetch.Name = "ObjsToFetch";
			this.ObjsToFetch.Size = new System.Drawing.Size(48, 20);
			this.ObjsToFetch.TabIndex = 5;
			this.ObjsToFetch.Text = "";
			this.ObjsToFetch.Validating += new CancelEventHandler(this.OnValidatingText);
			// 
			// label7
			// 
			this.label7.Location = new System.Drawing.Point(180, 52);
			this.label7.Name = "label7";
			this.label7.Size = new System.Drawing.Size(28, 16);
			this.label7.TabIndex = 5;
			this.label7.Text = "secs";
			this.label7.TextAlign = System.Drawing.ContentAlignment.MiddleLeft;
			// 
			// SortResultsCB
			// 
			this.SortResultsCB.Location = new System.Drawing.Point(296, 214);
			this.SortResultsCB.Name = "SortResultsCB";
			this.SortResultsCB.Size = new System.Drawing.Size(86, 14);
			this.SortResultsCB.TabIndex = 15;
			this.SortResultsCB.Text = "Sort Results";
			// 
			// CacheResultsCB
			// 
			this.CacheResultsCB.Checked = true;
			this.CacheResultsCB.CheckState = CheckState.Checked;
			this.CacheResultsCB.Location = new System.Drawing.Point(296, 238);
			this.CacheResultsCB.Name = "CacheResultsCB";
			this.CacheResultsCB.Size = new System.Drawing.Size(98, 14);
			this.CacheResultsCB.TabIndex = 16;
			this.CacheResultsCB.Text = "Cache Results";
			// 
			// label8
			// 
			this.label8.Location = new System.Drawing.Point(10, 246);
			this.label8.Name = "label8";
			this.label8.Size = new System.Drawing.Size(100, 14);
			this.label8.TabIndex = 17;
			this.label8.Text = "Results :";
			// 
			// ADQForm
			// 
			this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);
			this.ClientSize = new System.Drawing.Size(458, 525);
			this.Controls.Add(this.label8);
			this.Controls.Add(this.CacheResultsCB);
			this.Controls.Add(this.SortResultsCB);
			this.Controls.Add(this.groupBox3);
			this.Controls.Add(this.label4);
			this.Controls.Add(this.searchOptionCB);
			this.Controls.Add(this.groupBox2);
			this.Controls.Add(this.groupBox1);
			this.Controls.Add(this.ObjectView);
			this.Controls.Add(this.QueryButton);
			this.Controls.Add(this.ExitButton);
			this.FormBorderStyle = FormBorderStyle.FixedSingle;
			this.MaximizeBox = false;
			this.Name = "ADQForm";
			this.Text = "Querying Active Directory Service";
			this.groupBox1.ResumeLayout(false);
			this.groupBox2.ResumeLayout(false);
			this.groupBox3.ResumeLayout(false);
			this.ResumeLayout(false);

		}
		#endregion

		/// <summary>
		/// The main entry point for the application.
		/// </summary>
		[STAThread]
		static void Main() 
		{
			Application.Run(new ADQForm());
		}

		private void OnComputersCheckedChanged(object sender, System.EventArgs e)
		{
			ComputersFilter.Enabled = ComputersCB.Checked;
			FilterLabel2.Enabled = ComputersCB.Checked;
			if (ComputersCB.Checked)
				RootNode.Nodes.Add(ComputersNode);
			else
				RootNode.Nodes.Remove(ComputersNode);
			ObjectView.ExpandAll();
		}
		private void OnUsersCheckedChanged(object sender, System.EventArgs e)
		{
			UsersFilter.Enabled = UsersCB.Checked;
			FilterLabel1.Enabled = UsersCB.Checked;
			if (UsersCB.Checked)
				RootNode.Nodes.Add(UsersNode);
			else
				RootNode.Nodes.Remove(UsersNode);
			ObjectView.ExpandAll();
		}
		private void OnPrintersCheckedChanged(object sender, System.EventArgs e)
		{
			PrintersFilter.Enabled = PrintersCB.Checked;
			FilterLabel3.Enabled = PrintersCB.Checked;
			if (PrintersCB.Checked)
				RootNode.Nodes.Add(PrintersNode);
			else
				RootNode.Nodes.Remove(PrintersNode);
			ObjectView.ExpandAll();
		}

		// this function gets the immediate domain server name and adds it to tree
		private void GetRootNode()
		{
			// get the domain server for this computer
			DirectoryEntry de = new DirectoryEntry();
			// prepare a tree node with this domain controller name
			// the original name contains "DC=name"
			// remove the string DC=
			RootNode = new TreeNode(de.Name.Substring(3), 1, 1);
			// add the node to the tree view
			ObjectView.Nodes.Add(RootNode);
		}

		// form a filter string for the search in LDAP format
		private string FormFilter(string objectCategory, string filter)
		{
			String result;
			result = String.Format("(&(objectCategory={0})(name={1}))", objectCategory, filter);
			return result;
		}

		// this function forms the filter string based on the selected
		// objects on the form
		private string GetFilterString()
		{
			// form the filter string for directory search
			string filter = "";
			if (UsersCB.Checked)
				filter += FormFilter("user", UsersFilter.Text);
			if (ComputersCB.Checked)
				filter += FormFilter("computer", ComputersFilter.Text);
			if (PrintersCB.Checked)
				filter += FormFilter("printQueue", PrintersFilter.Text);

			// add all the above filter strings
			return "(|" + filter + ")";
		}

		// This function checks the type of object in the DirectoryEntry
		// and adds it to the object tree on the main form
		public void AddObjectToTree(DirectoryEntry de)
		{
			// before we add the name, remove the CN= from name
			if (String.Compare(de.SchemaClassName, "User", true)==0)
			{
				UsersNode.Nodes.Add(new TreeNode(de.Name.Substring(3)));
				UsersNode.Text = String.Format("Users ({0})", UsersNode.GetNodeCount(false));
			}
			if (String.Compare(de.SchemaClassName, "Computer", true)==0)
			{
				ComputersNode.Nodes.Add(new TreeNode(de.Name.Substring(3)));
				ComputersNode.Text = String.Format("Computers ({0})", ComputersNode.GetNodeCount(false));
			}
			if (String.Compare(de.SchemaClassName, "printQueue", true)==0)
			{
				PrintersNode.Nodes.Add(new TreeNode(de.Name.Substring(3)));
				PrintersNode.Text = String.Format("Printers ({0})", PrintersNode.GetNodeCount(false));
			}
			ObjectView.Update();
		}

		// Query Active Directory objects using .NET system.DirectoryServices
		private void QueryObjectsByNETClasses()
		{
			DirectorySearcher ds = new DirectorySearcher();
			ds.SearchRoot = new DirectoryEntry("");	// start searching from local domain
			ds.Filter = GetFilterString();		// get the LDAP filter string based on selections on the form
			ds.PropertyNamesOnly = true;		// this will get names of only those properties to which a value is set
			ds.PropertiesToLoad.Add("name");

			// (PageSize) Maximum number of objects the server will return per page
			// in a paged search. Default is 0, i.e. no paged search
			if (ObjsPerPage.Text.Length > 0) 
				ds.PageSize = Int32.Parse(ObjsPerPage.Text);

			// (ServerPageTimeLimit) the amount of time the server should observe to search a page of results
			// default is -1, i.e. search indefinitely
			if (PageTimeLimit.Text.Length > 0) 
				ds.ServerPageTimeLimit = new TimeSpan((long)(Decimal.Parse(PageTimeLimit.Text) * TimeSpan.TicksPerSecond));

			// (SizeLimit) maximum number of objects the server returns in a search
			// default is 0 - interpreted as server set default limit of 1000 entries
			if (ObjsToFetch.Text.Length > 0) 
				ds.SizeLimit = Int32.Parse(ObjsToFetch.Text);

			// (ServerTimeLimit) amount of time that the server should observe in a search
			// default is -1 interpreted as server default limit of 120 seconds 
			if (TotalTimeLimit.Text.Length > 0) 
				ds.ServerTimeLimit = new TimeSpan((long)(Decimal.Parse(TotalTimeLimit.Text) * TimeSpan.TicksPerSecond));

			// (SearchScope) option to search one level or complete subtree
			// default is Subtree, so set this option only if oneLevel is selected
			if (searchOptionCB.SelectedIndex == 1)
				ds.SearchScope = SearchScope.OneLevel;

			// (CacheResults) property by default is true
			ds.CacheResults = CacheResultsCB.Checked;

			ds.ReferralChasing = ReferralChasingOption.None;

			if (SortResultsCB.Checked)
				ds.Sort = new SortOption("name", SortDirection.Ascending);

			// change the cursor to wait cursor
			Cursor currentCursor = Cursor.Current;
			Cursor.Current = Cursors.WaitCursor;

			// start searching
			SearchResultCollection src = ds.FindAll();
			try 
			{
				foreach (SearchResult sr in src)
					AddObjectToTree(sr.GetDirectoryEntry());
			}
			catch (Exception e)
			{
				MessageBox.Show(e.Message);
			}
			src.Dispose();
			ds.Dispose();
			Cursor.Current = currentCursor;
		}

		private void OnExit(object sender, System.EventArgs e)
		{
			this.Close();
		}

		private void OnQuery(object sender, System.EventArgs e)
		{
			// if no option is checked then quit
			if (! (UsersCB.Checked || ComputersCB.Checked || PrintersCB.Checked))
				return;

			// clean the object tree
			UsersNode.Nodes.Clear();
			ComputersNode.Nodes.Clear();
			PrintersNode.Nodes.Clear();
			ObjectView.Update();
			ObjectView.ExpandAll();
			QueryObjectsByNETClasses();
		}

		// verify if a positive number is entered in a text box
		private void OnValidatingText(object sender, System.ComponentModel.CancelEventArgs e)
		{
			TextBox t = (TextBox)sender;
			if (t.Text.Length == 0) return;
			try 
			{
				if (Decimal.Parse(t.Text) < 0) throw new Exception();
			}
			catch (Exception) 
			{
				MessageBox.Show("Invalid entry. Please enter a correct value");
				e.Cancel = true;
			}
		}

	}
}