Implement IDispatch::Invoke to be called by a WebBrowser control

Question

I'm trying to do what they explain on this article in the Controlling Download and Execution section. I understand the Web Browser Control in that context is not .NET's WebBrowser.

What I'm trying to do is to gain control over what the WebBrowser control downloads. I've been searching for this a lot and always en up in the csEXWB, which has a huge code that I just cannot decipher.

What I've done so far is inherit .NET's WebBrowser, make my inherited class com visible by using the [ComVisible(true)] attribute, add this method to my class (taken from csEXWB):

    [DispId(HTMLDispIDs.DISPID_AMBIENT_DLCONTROL)]
    public int Idispatch_AmbiantDlControl_Invoke_Handler()
    {
        return (int)m_DLCtlFlags;
    }

And then call this line of code, where Browser is an instance of my derived class:

IfacesEnumsStructsClasses.IOleControl oleControl = Browser.ActiveXInstance as IfacesEnumsStructsClasses.IOleControl;
oleControl.OnAmbientPropertyChange(IfacesEnumsStructsClasses.HTMLDispIDs.DISPID_AMBIENT_DLCONTROL);

So what I'm hoping is that the oleControl will call my Idispatch_AmbiantDlControl_Invoke_Handler method, which it doesn't. I don't know how, and this is probably what my code is missing, is the oleControl supposed to know on which object to call my Idispatch_AmbiantDlControl_Invoke_Handler method.

What the article I linked above says is it will call your IDispatch::Invoke. What does it mean by your. How do I tell oleControl which object is my IDispatch. Hope I'm making any sense.

Answer 1

Here is a customized WebBrowser that allows you to change the DLCONTROL flags.

This is an example code:

public partial class Form1 : Form
{
    private MyWebBrowser _webBrowser;

    public Form1()
    {
        InitializeComponent();

        _webBrowser = new MyWebBrowser();
        _webBrowser.Dock = DockStyle.Fill;

        Controls.Add(_webBrowser);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        _webBrowser.DownloadControlFlags = (int)WebBrowserDownloadControlFlags.DOWNLOADONLY;
        _webBrowser.Navigate("http://mysamplewebsite");
    }
}

And the customized WebBrowser code:

public class MyWebBrowser : WebBrowser
{
    private const int DISPID_AMBIENT_DLCONTROL = -5512;
    private int _downloadControlFlags;

    // we want our site class, not the default one
    protected override WebBrowserSiteBase CreateWebBrowserSiteBase()
    {
        return new MyWebBrowserSite(this);
    }

    [DispId(DISPID_AMBIENT_DLCONTROL)]
    public int DownloadControlFlags
    {
        get
        {
            return _downloadControlFlags;
        }
        set
        {
            if (_downloadControlFlags == value)
                return;

            _downloadControlFlags = value;
            IOleControl ctl = (IOleControl)ActiveXInstance;
            ctl.OnAmbientPropertyChange(DISPID_AMBIENT_DLCONTROL);
        }
    }

    protected class MyWebBrowserSite : WebBrowserSite, IReflect
    {
        private Dictionary<int, PropertyInfo> _dispidCache;
        private MyWebBrowser _host;

        public MyWebBrowserSite(MyWebBrowser host)
            : base(host)
        {
            _host = host;
        }

        object IReflect.InvokeMember(string name, BindingFlags invokeAttr, Binder binder, object target, object[] args, ParameterModifier[] modifiers, CultureInfo culture, string[] namedParameters)
        {
            object ret = null;
            // Check direct IDispatch call using a dispid (see http://msdn.microsoft.com/en-us/library/de3dhzwy.aspx)
            const string dispidToken = "[DISPID=";
            if (name.StartsWith(dispidToken))
            {
                int dispid = int.Parse(name.Substring(dispidToken.Length, name.Length - dispidToken.Length - 1));
                if (_dispidCache == null)
                {
                    // WebBrowser has many properties, so we build a dispid cache on it
                    _dispidCache = new Dictionary<int, PropertyInfo>();
                    foreach (PropertyInfo pi in _host.GetType().GetProperties(BindingFlags.Public | BindingFlags.Instance))
                    {
                        if ((!pi.CanRead) || (pi.GetIndexParameters().Length > 0))
                            continue;

                        object[] atts = pi.GetCustomAttributes(typeof(DispIdAttribute), true);
                        if ((atts != null) && (atts.Length > 0))
                        {
                            DispIdAttribute da = (DispIdAttribute)atts[0];
                            _dispidCache[da.Value] = pi;
                        }
                    }
                }

                PropertyInfo property;
                if (_dispidCache.TryGetValue(dispid, out property))
                {
                    ret = property.GetValue(_host, null);
                }
            }
            return ret;
        }

        FieldInfo[] IReflect.GetFields(BindingFlags bindingAttr)
        {
            return GetType().GetFields(bindingAttr);
        }

        MethodInfo[] IReflect.GetMethods(BindingFlags bindingAttr)
        {
            return GetType().GetMethods(bindingAttr);
        }

        PropertyInfo[] IReflect.GetProperties(BindingFlags bindingAttr)
        {
            return GetType().GetProperties(bindingAttr);
        }

        FieldInfo IReflect.GetField(string name, BindingFlags bindingAttr)
        {
            throw new NotImplementedException();
        }

        MemberInfo[] IReflect.GetMember(string name, BindingFlags bindingAttr)
        {
            throw new NotImplementedException();
        }

        MemberInfo[] IReflect.GetMembers(BindingFlags bindingAttr)
        {
            throw new NotImplementedException();
        }

        MethodInfo IReflect.GetMethod(string name, BindingFlags bindingAttr)
        {
            throw new NotImplementedException();
        }

        MethodInfo IReflect.GetMethod(string name, BindingFlags bindingAttr, Binder binder, Type[] types, ParameterModifier[] modifiers)
        {
            throw new NotImplementedException();
        }

        PropertyInfo IReflect.GetProperty(string name, BindingFlags bindingAttr, Binder binder, Type returnType, Type[] types, ParameterModifier[] modifiers)
        {
            throw new NotImplementedException();
        }

        PropertyInfo IReflect.GetProperty(string name, BindingFlags bindingAttr)
        {
            throw new NotImplementedException();
        }

        Type IReflect.UnderlyingSystemType
        {
            get { throw new NotImplementedException(); }
        }
    }

    [ComImport, InterfaceType(ComInterfaceType.InterfaceIsIUnknown), Guid("B196B288-BAB4-101A-B69C-00AA00341D07")]
    internal interface IOleControl
    {
        void Reserved0();
        void Reserved1();
        void OnAmbientPropertyChange(int dispID);
        void Reserved2();
    }
}

[Flags]
public enum WebBrowserDownloadControlFlags: uint
{
    DLIMAGES                          = 0x00000010,
    VIDEOS                            = 0x00000020,
    BGSOUNDS                          = 0x00000040,
    NO_SCRIPTS                        = 0x00000080,
    NO_JAVA                           = 0x00000100,
    NO_RUNACTIVEXCTLS                 = 0x00000200,
    NO_DLACTIVEXCTLS                  = 0x00000400,
    DOWNLOADONLY                      = 0x00000800,
    NO_FRAMEDOWNLOAD                  = 0x00001000,
    RESYNCHRONIZE                     = 0x00002000,
    PRAGMA_NO_CACHE                   = 0x00004000,
    NO_BEHAVIORS                      = 0x00008000,
    NO_METACHARSET                    = 0x00010000,
    URL_ENCODING_DISABLE_UTF8         = 0x00020000,
    URL_ENCODING_ENABLE_UTF8          = 0x00040000,
    NOFRAMES                          = 0x00080000,
    FORCEOFFLINE                      = 0x10000000,
    NO_CLIENTPULL                     = 0x20000000,
    SILENT                            = 0x40000000,
    OFFLINEIFNOTCONNECTED             = 0x80000000,
    OFFLINE                           = OFFLINEIFNOTCONNECTED,
}