Enumerate and Host Control Panel Applets using C#.

using System;
using System.Text;
using System.Drawing;
using System.Collections;
using System.Runtime.InteropServices;

namespace AppletEngine
{
	/// <summary>
	/// The standard Control Panel Applet Information structure
	/// </summary>
	[StructLayout(LayoutKind.Sequential)]
	public struct CPLINFO
	{
		/// <summary>
		/// The resource Id of the icon the applet wishes to display
		/// </summary>
		public int IconResourceId;

		/// <summary>
		/// The resource Id of the name the applet wishes to display
		/// </summary>
		public int NameResourceId;     

		/// <summary>
		/// The resource Id of the information the applet wishes to display (aka. Description)
		/// </summary>
		public int InformationResourceId;

		/// <summary>
		/// A pointer to applet defined data
		/// </summary>
		public IntPtr AppletDefinedData;    

		/// <summary>
		/// A simple override to display some debugging information about the resource ids returned from each applet
		/// </summary>
		/// <returns></returns>
		public override string ToString()
		{
			return string.Format("IconResourceId: {0}, NameResourceId: {1}, InformationResourceId: {2}, AppletDefinedData: {3}", IconResourceId.ToString(), NameResourceId.ToString(), InformationResourceId.ToString(), AppletDefinedData.ToInt32().ToString("X"));
		}
	}

	/// <summary>
	/// The advanced Control Panel Applet Information structure
	/// </summary>
	[StructLayout(LayoutKind.Sequential, CharSet=CharSet.Ansi)]
	public struct NEWCPLINFO
	{
		/// <summary>
		/// The size of the NEWCPLINFO structure 
		/// </summary>
		public int Size;

		/// <summary>
		/// This field is unused
		/// </summary>
		public int Flags;

		/// <summary>
		/// This field is unused
		/// </summary>
		public int HelpContext;

		/// <summary>
		/// A pointer to applet defined data
		/// </summary>
		public IntPtr AppletDefinedData;

		/// <summary>
		/// A handle to an icon that the applet wishes to display
		/// </summary>
		public IntPtr hIcon;

		/// <summary>
		/// An array of chars that contains the name that the applet wishes to display
		/// </summary>
		[MarshalAs(UnmanagedType.ByValTStr, SizeConst=32)]
		public string NameCharArray;

		/// <summary>
		/// An array of chars that contains the information that the applet wishes to display
		/// </summary>
		[MarshalAs(UnmanagedType.ByValTStr, SizeConst=64)]
		public string InfoCharArray;

		/// <summary>
		/// An array of chars that contains the help file that the applet wishes to display for further help
		/// </summary>
		[MarshalAs(UnmanagedType.ByValTStr, SizeConst=128)]
		public string HelpFileCharArray;
	}

	/// <summary>
	/// The Applet class exposes methods for displaying information about a single Control Panel Applet as well as opening and closing the applet. Some applets may not function properly without Windows Explorer (explorer.exe) running as the Windows Shell.
	/// </summary>
	public class Applet : DisposableObject
	{
		private Bitmap _smallImage;
		private Bitmap _largeImage;		
		private string _name = null;
		private string _description = null;
		private AppletLibrary _appletLibrary = null;
		private int _appletIndex = 0;
		private CPLINFO _info;
		private IntPtr _infoPtr;
		private NEWCPLINFO _dynInfo;
		private IntPtr _dynInfoPtr;
		public const int DynamicResource = 0;

		#region P/Invoke

		[DllImport("User32")]
		public static extern IntPtr GetDesktopWindow();

		[DllImport("User32")]
		public static extern int LoadString(IntPtr hLib, uint uID, StringBuilder sb, int sbSize);
		
		[DllImport("AppletProxy")]
		public static extern IntPtr LoadAppletIcon(IntPtr hLib, int resId);

		[DllImport("AppletProxy")]
		public static extern IntPtr LoadAppletImage(IntPtr hLib, int resId, int width, int height);

		#endregion

		#region DisposableObject Overrides

		public override void Dispose(bool disposing)
		{
			base.Dispose (disposing);

			if (disposing)
			{

			}
			
			if (!base.IsNullPtr(_infoPtr))
			{
				Marshal.FreeHGlobal(_infoPtr);
				_infoPtr = IntPtr.Zero;
			}

			if (!base.IsNullPtr(_dynInfoPtr))
			{
				Marshal.FreeHGlobal(_dynInfoPtr);
				_dynInfoPtr = IntPtr.Zero;
			}
		}

		#endregion

		/// <summary>
		/// Initializes a new instance of the Applet class
		/// </summary>
		/// <param name="appletLibrary">The AppletLibrary that contains this Applet</param>
		/// <param name="appletIndex">The index of the Applet in it's AppletLibrary</param>
		public Applet(AppletLibrary appletLibrary, int appletIndex)
		{
			_appletLibrary = appletLibrary;
			_appletIndex = appletIndex;
			this.Inquire();	
		}

		/// <summary>
		/// Inquires the information about the Applet, caches items such as Name, Description, and Icon.
		/// </summary>
		public void Inquire()
		{
			unsafe
			{
				_info = new CPLINFO();
				_infoPtr = Marshal.AllocHGlobal(sizeof(CPLINFO));
				Marshal.StructureToPtr(_info, _infoPtr, true);
				if (!base.IsNullPtr(_infoPtr))
				{
					_appletLibrary.CPlApplet(AppletMessages.Inquire, new IntPtr(_appletIndex), _infoPtr);
					_info = (CPLINFO)Marshal.PtrToStructure(_infoPtr, typeof(CPLINFO));
					
					if (!this.IsUsingDynamicResources)
					{
						this.ExtractNameFromResources();
						this.ExtractDescriptionFromResources();
						this.ExtractIconFromResources();
					}
					else
					{
						this.NewInquire();
					}
				}
			}
		}

		public void NewInquire()
		{
		//			unsafe
		//			{
				_dynInfo = new NEWCPLINFO();
				_dynInfo.Size = Marshal.SizeOf(_dynInfo); 
				_dynInfoPtr = Marshal.AllocHGlobal(_dynInfo.Size);
				Marshal.StructureToPtr(_dynInfo, _dynInfoPtr, true);
				if (!base.IsNullPtr(_dynInfoPtr))
				{
					_appletLibrary.CPlApplet(AppletMessages.NewInquire, new IntPtr(_appletIndex), _dynInfoPtr);
					_dynInfo = (NEWCPLINFO)Marshal.PtrToStructure(_dynInfoPtr, typeof(NEWCPLINFO));

					_smallImage = Bitmap.FromHicon(_dynInfo.hIcon);
					_largeImage = Bitmap.FromHicon(_dynInfo.hIcon);					
					_name = _dynInfo.NameCharArray.ToString();					
					_description = _dynInfo.InfoCharArray.ToString();
				}
		//			}
		}

		public bool IsUsingDynamicResources
		{
			get
			{
				return (_info.IconResourceId == DynamicResource || _info.NameResourceId == DynamicResource || _info.InformationResourceId == DynamicResource);
			}
		}

		

		private void ExtractNameFromResources()
		{
			try
			{
				int size = 260;
				StringBuilder sb = new StringBuilder(size);
				int length = LoadString(_appletLibrary.LibraryHandle, (uint)_info.NameResourceId, sb, size);
				if (length > 0)
				{
					_name = sb.ToString();
				}
			}
			catch(System.Exception systemException)
			{
				System.Diagnostics.Trace.WriteLine(systemException);
			}
		}

		private void ExtractDescriptionFromResources()
		{
			try
			{
				int size = 260;
				StringBuilder sb = new StringBuilder(size);
				int length = LoadString(_appletLibrary.LibraryHandle, (uint)_info.InformationResourceId, sb, size);
				if (length > 0)
				{
					_description = sb.ToString();
				}
			}
			catch(System.Exception systemException)
			{
				System.Diagnostics.Trace.WriteLine(systemException);
			}
		}

		private void ExtractIconFromResources()
		{
			try
			{				
				IntPtr hSmall = LoadAppletImage(_appletLibrary.LibraryHandle, _info.IconResourceId, 16, 16);
				IntPtr hLarge = LoadAppletImage(_appletLibrary.LibraryHandle, _info.IconResourceId, 32, 32);

				if (!base.IsNullPtr(hSmall))
				{
					_smallImage = Bitmap.FromHicon(hSmall);
				}

				if (!base.IsNullPtr(hLarge))
				{
					_largeImage = Bitmap.FromHicon(hLarge);
				}
			}
			catch(System.Exception systemException)
			{
				System.Diagnostics.Trace.WriteLine(systemException);
			}
		}

		public Bitmap SmallImage
		{
			get
			{
				return _smallImage;
			}
		}

		public Bitmap LargeImage
		{
			get
			{
				return _largeImage;
			}
		}

		/// <summary>
		/// Gets the Name to display for the Applet
		/// </summary>
		public string Name
		{
			get
			{
				return _name;
			}
		}

		/// <summary>
		/// Gets the Description to display for the Applet
		/// </summary>
		public string Description
		{
			get
			{
				return _description;
			}
		}

		/// <summary>
		/// Opens the Applet's configuration dialog
		/// </summary>
		public void Open()
		{
			IntPtr userData = (this.IsUsingDynamicResources ? _info.AppletDefinedData : _dynInfo.AppletDefinedData);
			int result = _appletLibrary.CPlApplet(AppletMessages.DoubleClick, new IntPtr(_appletIndex), userData);
			if (result != 0)
			{
				System.ComponentModel.Win32Exception e = new System.ComponentModel.Win32Exception();
				System.Diagnostics.Trace.WriteLine(e);
			}
		}

		/// <summary>
		/// Closes the Applet's configuration dialog
		/// </summary>
		public void Close()
		{
			IntPtr userData = (this.IsUsingDynamicResources ? _info.AppletDefinedData : _dynInfo.AppletDefinedData);
			_appletLibrary.CPlApplet(AppletMessages.Stop, new IntPtr(_appletIndex), userData);
		}

		public override string ToString()
		{
			return string.Format("Applet ({0}), Name: {1}, Description: {2}", System.IO.Path.GetFileName(_appletLibrary.Path), _name, _description);
		}
	}
}