HOWTO: Use the undocumented HTMLLITE.DLL component

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Drawing;

namespace WindowsApplication1
{

   /// 

   /// 
   /// A managed wrapper for htmllite.dll
   /// 
   /// Important: htmllite.dll must be on the system PATH in order
   /// for this control to work in design-time.
   /// 
   /// This code was built against htmllite.dll version 8.0.50727.42
   ///
   /// Nothing terribly interesting here, just one new property and
   /// one event.
   ///
   /// 

   
   
   public class HTMLLiteControl : System.Windows.Forms.TextBox
   {
      public HTMLLiteControl() 
      {
         this.AutoSize = false;
         this.Multiline = true;
         this.SetStyle( ControlStyles.ResizeRedraw, true );
      }

      [DllImport( "htmllite.dll", CallingConvention = CallingConvention.StdCall,
         EntryPoint = "_FRegisterHtmlLiteClass@4" )]
      public static extern void RegisterHtmlLite( int zero );


      private const int WM_ERASEBKGND = 0x0014;
      private const int WM_NOTIFY = 0x004E;

      private const int HTMLLITE_CODE_LEFTCLICK     = 1000; //A link has been clicked either via the Mouse or Spacebar key
      private const int HTMLLITE_CODE_TABCYCLE      = 1001; //A link has received focus due to the Tab Cycle, or Keyboard Arrow Keys
      private const int HTMLLITE_CODE_RIGHTCLICK    = 1003; //A link has been right-clicked, and already had focus
      private const int HTMLLITE_CODE_MOUSEOVER     = 1004; //Mouse is over a link
      private const int HTMLLITE_CODE_MOUSEHOVER    = 1005; //Mouse is hovering a link (~1 second = hover)
      private const int HTMLLITE_CODE_MOUSEEXIT     = 1006; //Mouse has left a link's rectangle   


      [StructLayout(LayoutKind.Sequential)]
      public struct RECT
      {
         public int left;
         public int top;
         public int right;
         public int bottom;
      }


      [StructLayout(LayoutKind.Sequential)]
      public struct NMHTMLLITE 
      {
         public IntPtr  hwndFrom;  
         public IntPtr  idFrom;     
         public IntPtr  code;    
         public IntPtr  linkid;         
         public RECT linkrc;
      }

      protected override void OnHandleCreated( EventArgs e )
      {
         base.OnHandleCreated( e );
         IntPtr hwndParent = GetParent( this.Handle );
         if( hwndParent != IntPtr.Zero )
         {
            if( parentHook != null && parentHook.Handle != IntPtr.Zero )
               parentHook.ReleaseHandle();
            if( parentHook == null )
            {
               parentHook = new ParentHook( this, hwndParent );
            }
         }
      }

      protected override void OnHandleDestroyed( EventArgs e )
      {
         if( this.parentHook != null )
            this.parentHook.ReleaseHandle();
      }

      [DllImport( "user32" )]
      private static extern IntPtr GetParent( IntPtr hwnd );

      protected override CreateParams CreateParams
      {
         get
         {
            RegisterHtmlLite( 0 );
            CreateParams createParams = base.CreateParams;
            createParams.ClassName = "HTMLLITE";
            return createParams;
         }
      }

      protected void OnParentNotify( NMHTMLLITE hdr )
      {
         if( hdr.hwndFrom == this.Handle && hdr.code.ToInt32() == HTMLLITE_CODE_LEFTCLICK )
            OnLinkClicked( hdr.linkid.ToInt32() );
      }

      protected virtual void OnLinkClicked( int linkId )
      {
         if( this.LinkClicked != null )
            this.LinkClicked( this, new LinkClickedEventArgs( linkId ) );
      }

      private class ParentHook : NativeWindow
      {
         public ParentHook( HTMLLiteControl owner, IntPtr hwndParent )
         {
            ownerControl = owner;
            AssignHandle( hwndParent );
         }
         private HTMLLiteControl ownerControl = null;
         protected override void WndProc( ref Message m )
         {
            if( m.Msg == WM_NOTIFY && m.LParam != IntPtr.Zero )
            {
               NMHTMLLITE hdr = (NMHTMLLITE) m.GetLParam( typeof( NMHTMLLITE ) );
               int code = hdr.code.ToInt32();
               if( code >= HTMLLITE_CODE_LEFTCLICK && code <= HTMLLITE_CODE_MOUSEEXIT )
                  ownerControl.OnParentNotify( hdr );
            }
            base.WndProc( ref m );
         }
      }

      private ParentHook parentHook = null;

      protected override void WndProc( ref Message m )
      {
         switch( m.Msg )
         {
            case WM_ERASEBKGND:
               using( Graphics screenGraphics = Graphics.FromHdc( m.WParam ) )
               using( Brush b = new SolidBrush( this.BackColor ) )
                  screenGraphics.FillRectangle( b, this.ClientRectangle );
               break;
         }
         base.WndProc( ref m );
      }


      /// 

      /// HTML Property
      /// 
      /// Gets/sets the HTML source (read the Text property
      /// to get the formatted text).
      /// 


      public string HTML
      {
         get
         {
            return html;
         }
         set
         {
            base.Text = value;
            html = value;
         }
      }

      private string html = string.Empty;

      /// 

      /// Fired when a link is clicked, with the linkid passed
      /// in the event arguments.
      /// 


      public event EventHandler<LinkClickedEventArgs> LinkClicked = null;
   }

   public class LinkClickedEventArgs : System.EventArgs
   {
      public LinkClickedEventArgs(int linkId)
      {
         this.LinkId = linkId;
      }
      public int LinkId = 0;
   }
}

<style>
.titlerow { highlight: black; color: white; padding: 5; }
.leftcol { margin-top: auto; width: 200; highlight: #003399; color: white; padding: 5; }
.rightcol { margin-top: previous; margin-left: 200; padding:5; highlight: white; }
.bottom { margin-top: auto; align: right; highlight: infobackground; color: infotext; padding: 5; }
</style>
<p class="titlerow">Sample Page #1</p>
<p class="leftcol">Left Column<br>This is the left column.<br> </p>
<p class="rightcol">Right Column<br>This is the right column.<br> </p>
<p class="bottom">Exit</p>