Mouse Events for WebBrowser control in .NET CF

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Introduction

Nearly, in one of my .NET Compact Framework 2.0 projects, I want to use the WebBrowser control to display rich-media content. Unfortunately, the WebBrowser control in the .NET CF is not as powerful as the .NET Framework's control. It does not have some of the useful interfaces, especially it does not support DOM model... My requirements for the control are:

• Doesn't have the progress bar at the bottom.
• Doesn't use the default context menu (disable it, or even better, I can customize the context menu).
• Has a way to append HTML text into it (DocumentText or something like that).
• Can handle Mouse events (MouseUp, MouseDown, MouseMove).

The OpenNETCF's SDF WebBrowser control does satisfy the first three requirements, but it still cannot handle mouse events. So I decided to expand the standard WebBrowser control so that it can play with mouse events.

Background

In the .NET Framework, using the Document property, we can easily handle mouse events for the WebBrowser control; but the .NET CF doesn't. Because when the user clicks on the WebBrowser control, he actually clicks on the Document that the control hosts, so the WebBrowser does not know this event, and of course it doesn't raise the correlative events.

The idea to solve the problem: derive the WebBrowser control, and hook all of the mouse events which occur inside the control. Thanks to OpenNETCF's ApplicationEx class, we can achieve this in managed code. Concretely, we write a class called WebBrowserEx, which is derived from .NET CF's WebBrowser control, and implement the IMessageFilter interface. This interface will help us to hook and catch WM_LBUTTONUP, WM_LBUTTONDOWN and WM_MOUSEMOVE message. (If you aren't familiar with IMessageFiter, you should go to the OpenNETCF's website and have a look).

But, when you click on the WebBrowser, which is the child window receives these messages? Not a problem! Using the Remote Spy utility (in the Visual Studio Remote Tools), we can see a grandchild window of the WebBrowser control. This window belongs to PIEHTML class and receives all of the mouse messages.

Implementation

There are only approximate 100 lines of code in the WebBrowserEx class, so I paste all here.

using System;
using System.Runtime.InteropServices;
using System.Windows.Forms;
using OpenNETCF.Windows.Forms;
using OpenNETCF.Win32;
using Microsoft.WindowsCE.Forms;

namespace webBrowserEx
{
    /// <summary>
    /// An extended WebBrowser, can handle Mouse Events.
    /// </summary>
    public class WebBrowserEx : System.Windows.Forms.WebBrowser, IMessageFilter
    {

        public WebBrowserEx()
        {
            //Initialize Message Filter, using OpenNETCF's ApplicationEx
            OpenNETCF.Windows.Forms.ApplicationEx.AddMessageFilter(this);
        }

        #region ------ IMessageFilter implementation ------

        public bool PreFilterMessage(ref Message m)
        {
            if ((m.Msg == (int)WM.LBUTTONDOWN || m.Msg == (int)WM.LBUTTONUP || 
			m.Msg == (int)WM.MOUSEMOVE)
                 && IsChildestWindow(this.Handle, m.HWnd))
            {
                int xPos = (int)m.LParam & 0xFFFF;
                int yPos = ((int)m.LParam >> 16) & 0xFFFF;

                MouseEventArgs e = new MouseEventArgs(MouseButtons.Left, 1,
                                        xPos, yPos, 0);

                switch (m.Msg)
                {
                    case (int)WM.LBUTTONUP:
                        base.OnMouseUp(e);
                        break;
                    case (int)WM.LBUTTONDOWN:
                        base.OnMouseDown(e);
                        break;
                    case (int)WM.MOUSEMOVE:
                        base.OnMouseMove(e);
                        break;
                }
            }

            return false;
        }

        #endregion

        #region ------- Private functions -----------------

        /// <summary>
        /// Check whether <see cref="hCheck"/> 
        /// is one of <see cref="hWnd"/>'s grandchildren.
        /// </summary>
        /// <param name="hWnd"></param>
        /// <param name="hCheck"></param>
        /// <returns></returns>
        private static bool IsChildestWindow(IntPtr hWnd, IntPtr hCheck)
        {
            IntPtr ret = hWnd;

            //Find the first "smallest" child
            while ((hWnd = GetWindow(hWnd, (int)GetWindowFlags.GW_CHILD)) != IntPtr.Zero)
            {
                ret = hWnd;
            }
            
            //goes through all of "smallest" grandchildren
            hWnd = ret;
            while ((ret != hCheck) &&
                ((hWnd = GetWindow(ret, (int)GetWindowFlags.GW_HWNDNEXT)) != IntPtr.Zero))
            {
                ret = hWnd;
            }

            return (hWnd != IntPtr.Zero);
        }

        #endregion

        #region -------- P/Invoke declarations ------------

        /// <summary>
        /// Get relative window with a given window.
        /// </summary>
        /// <param name="hwnd">the Given window</param>
        /// <param name="cmd">an <see cref="GetWindowFlags"/> value, 
        /// indicates the relation.</param>
        /// <returns></returns>
        [DllImport("coredll.dll")]
        private static extern IntPtr GetWindow(IntPtr hwnd, int cmd);

        private enum GetWindowFlags : int
        {
            GW_HWNDFIRST = 0,
            GW_HWNDLAST = 1,
            GW_HWNDNEXT = 2,
            GW_HWNDPREV = 3,
            GW_OWNER = 4,
            GW_CHILD = 5,
            GW_MAX = 5
        }

        #endregion
    }
}

The implementation is so easy. Whenever receiving a WM_MOUSEMOVE, WM_LBUTTONUP, WM_LBUTTONDOWN message, we will check if the m.HWnd is a grandchild of the WebBrowser (i.e. the PIEHTML window) and raise the correlative events.

The last thing we have to do is use the OpenNETCF.Windows.Forms.ApplicationEx class to run the application, instead of System.Windows.Forms.Application. This will help in receiving and processing messages in the PreFilterMessage function. We place this code in Program.cs:

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [MTAThread]
    static void Main()
    {            
        // Instead of using Application class,
        // we use OpenNETCF's ApplicationEx which enables MessageFilter.
        OpenNETCF.Windows.Forms.ApplicationEx.Run(new Form1());
        //Application.Run(new Form1());
    }
} 

Points of Interest

• I built the sample code in VS 2008, using Smart Device Project on .NET Compact Framework 2.0. But in .NET CF 3.5, it should be fine.
• Instead of using System.Windows.Forms.WebBrowser, you can use the OpenNETCF.Windows.Forms.WebBrowser class. In that case, you only have to replace System.Windows.Forms.WebBrowser by OpenNETCF.Windows.Forms.WebBrowser:

  /// <summary>
  /// An extended WebBrowser, can handle Mouse Events.
  /// </summary>
  public class WebBrowserEx : OpenNETCF.Windows.Forms.WebBrowser, IMessageFilter
  { 
      //.... 
  }

  Derived from OpenNETCF's WebBrowser, you can use WebBrowserEx in .NET CF 1.0, and it has built-in functions such as: disabled the default context menu, doesn't have the progress bar...

Through the years, I learnt a lot of interesting things from CodeProject, but this is my first article, with a shy code... So, feel free to comment and... ^^.

Sorry for my English, it's not my mother language.

History

• July 13, 2008: Article submitted