Here's a complete WinForms-based example that works, IDocHostUIHandler.GetDropTarget does get called.
using System;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Windows.Forms;
namespace CustomWebBrowser
{
public partial class MainForm : Form
{
public MainForm()
{
InitializeComponent();
}
private void MainForm_Load(object sender, EventArgs e)
{
var wb = new ImprovedWebBrowser();
wb.Dock = DockStyle.Fill;
this.Controls.Add(wb);
wb.Visible = true;
wb.DocumentText = "<body contentEditable='true'><b>Hello from ImprovedWebBrowser!</b></body>";
}
}
public class ImprovedWebBrowser : WebBrowser
{
/// <summary>
/// provide custom WebBrowserSite,
/// where we override IDocHostUIHandler and call the base implementation
/// More info: http://stackoverflow.com/a/19739699/1768303
/// </summary>
protected override WebBrowserSiteBase CreateWebBrowserSiteBase()
{
return new ImprovedWebBrowserSite(this);
}
#region ImprovedWebBrowserSite
[ClassInterface(ClassInterfaceType.None)]
protected class ImprovedWebBrowserSite :
WebBrowserSite,
NativeMethods.IDocHostUIHandler,
IDisposable,
ICustomQueryInterface
{
ImprovedWebBrowser _host;
NativeMethods.IDocHostUIHandler _baseIDocHostUIHandler;
IntPtr _unkInnerAggregated;
IntPtr _unkOuter;
Inner _inner;
// constructor
public ImprovedWebBrowserSite(WebBrowser host) :
base(host)
{
_host = (ImprovedWebBrowser)host;
// get the CCW object for this
_unkOuter = Marshal.GetIUnknownForObject(this);
Marshal.AddRef(_unkOuter);
try
{
// aggregate the CCW object with the helper Inner object
_inner = new Inner(this);
_unkInnerAggregated = Marshal.CreateAggregatedObject(_unkOuter, _inner);
// obtain private WebBrowserSite COM interfaces
_baseIDocHostUIHandler = (NativeMethods.IDocHostUIHandler)Marshal.GetTypedObjectForIUnknown(_unkInnerAggregated, typeof(NativeMethods.IDocHostUIHandler));
}
finally
{
Marshal.Release(_unkOuter);
}
}
~ImprovedWebBrowserSite()
{
// need to work out the reference counting for GC to work correctly
Debug.Print("ImprovedWebBrowserSite object finalized.");
}
void IDisposable.Dispose()
{
base.Dispose();
_baseIDocHostUIHandler = null;
if (_unkInnerAggregated != IntPtr.Zero)
{
Marshal.Release(_unkInnerAggregated);
_unkInnerAggregated = IntPtr.Zero;
}
if (_unkOuter != IntPtr.Zero)
{
Marshal.Release(_unkOuter);
_unkOuter = IntPtr.Zero;
}
}
#region Inner
// Inner as aggregated object
class Inner :
ICustomQueryInterface,
IDisposable
{
object _outer;
Type[] _interfaces;
public Inner(object outer)
{
_outer = outer;
_interfaces = _outer.GetType().BaseType.GetInterfaces();
}
public CustomQueryInterfaceResult GetInterface(ref Guid iid, out IntPtr ppv)
{
if (_outer != null)
{
var guid = iid;
var iface = _interfaces.FirstOrDefault((t) => t.GUID == guid);
if (iface != null)
{
var unk = Marshal.GetComInterfaceForObject(_outer, iface, CustomQueryInterfaceMode.Ignore);
if (unk != IntPtr.Zero)
{
ppv = unk;
return CustomQueryInterfaceResult.Handled;
}
}
}
ppv = IntPtr.Zero;
return CustomQueryInterfaceResult.Failed;
}
~Inner()
{
// need to work out the reference counting for GC to work correctly
Debug.Print("Inner object finalized.");
}
public void Dispose()
{
_outer = null;
_interfaces = null;
}
}
#endregion
#region ICustomQueryInterface
public CustomQueryInterfaceResult GetInterface(ref Guid iid, out IntPtr ppv)
{
// CustomQueryInterfaceMode.Ignore is to avoid infinite loop during QI.
if (iid == typeof(NativeMethods.IDocHostUIHandler).GUID)
{
ppv = Marshal.GetComInterfaceForObject(this, typeof(NativeMethods.IDocHostUIHandler), CustomQueryInterfaceMode.Ignore);
}
else
{
ppv = IntPtr.Zero;
return CustomQueryInterfaceResult.NotHandled;
}
return CustomQueryInterfaceResult.Handled;
}
#endregion
#region IDocHostUIHandler
int NativeMethods.IDocHostUIHandler.ShowContextMenu(int dwID, ref NativeMethods.POINT pt, IntPtr pcmdtReserved, IntPtr pdispReserved)
{
return _baseIDocHostUIHandler.ShowContextMenu(dwID, ref pt, pcmdtReserved, pdispReserved);
}
int NativeMethods.IDocHostUIHandler.GetHostInfo(ref NativeMethods.DOCHOSTUIINFO info)
{
Debug.Print("IDocHostUIHandler.GetHostInfo");
return _baseIDocHostUIHandler.GetHostInfo(ref info);
}
int NativeMethods.IDocHostUIHandler.ShowUI(int dwID, IntPtr activeObject, IntPtr commandTarget, IntPtr frame, IntPtr doc)
{
return _baseIDocHostUIHandler.ShowUI(dwID, activeObject, commandTarget, frame, doc);
}
int NativeMethods.IDocHostUIHandler.HideUI()
{
return _baseIDocHostUIHandler.HideUI();
}
int NativeMethods.IDocHostUIHandler.UpdateUI()
{
return _baseIDocHostUIHandler.UpdateUI();
}
int NativeMethods.IDocHostUIHandler.EnableModeless(bool fEnable)
{
return _baseIDocHostUIHandler.EnableModeless(fEnable);
}
int NativeMethods.IDocHostUIHandler.OnDocWindowActivate(bool fActivate)
{
return _baseIDocHostUIHandler.OnDocWindowActivate(fActivate);
}
int NativeMethods.IDocHostUIHandler.OnFrameWindowActivate(bool fActivate)
{
return _baseIDocHostUIHandler.OnFrameWindowActivate(fActivate);
}
int NativeMethods.IDocHostUIHandler.ResizeBorder(ref NativeMethods.COMRECT rect, IntPtr doc, bool fFrameWindow)
{
return _baseIDocHostUIHandler.ResizeBorder(ref rect, doc, fFrameWindow);
}
int NativeMethods.IDocHostUIHandler.TranslateAccelerator(ref NativeMethods.MSG msg, ref Guid group, int nCmdID)
{
return _baseIDocHostUIHandler.TranslateAccelerator(ref msg, ref group, nCmdID);
}
int NativeMethods.IDocHostUIHandler.GetOptionKeyPath(string[] pbstrKey, int dw)
{
return _baseIDocHostUIHandler.GetOptionKeyPath(pbstrKey, dw);
}
int NativeMethods.IDocHostUIHandler.GetDropTarget(IntPtr pDropTarget, out IntPtr ppDropTarget)
{
Debug.Print("IDocHostUIHandler.GetDropTarget");
return _baseIDocHostUIHandler.GetDropTarget(pDropTarget, out ppDropTarget);
}
int NativeMethods.IDocHostUIHandler.GetExternal(out object ppDispatch)
{
return _baseIDocHostUIHandler.GetExternal(out ppDispatch);
}
int NativeMethods.IDocHostUIHandler.TranslateUrl(int dwTranslate, string strURLIn, out string pstrURLOut)
{
return _baseIDocHostUIHandler.TranslateUrl(dwTranslate, strURLIn, out pstrURLOut);
}
int NativeMethods.IDocHostUIHandler.FilterDataObject(IntPtr pDO, out IntPtr ppDORet)
{
return _baseIDocHostUIHandler.FilterDataObject(pDO, out ppDORet);
}
#endregion
}
#endregion
}
public static class NativeMethods
{
#region IDocHostUIHandler
public enum DOCHOSTUIDBLCLICK
{
DEFAULT = 0x0,
SHOWPROPERTIES = 0x1,
SHOWCODE = 0x2
}
public enum DOCHOSTUIFLAG
{
DIALOG = 0x1,
DISABLE_HELP_MENU = 0x2,
NO3DBORDER = 0x4,
SCROLL_NO = 0x8,
DISABLE_SCRIPT_INACTIVE = 0x10,
OPENNEWWIN = 0x20,
DISABLE_OFFSCREEN = 0x40,
FLAT_SCROLLBAR = 0x80,
DIV_BLOCKDEFAULT = 0x100,
ACTIVATE_CLIENTHIT_ONLY = 0x200,
NO3DOUTERBORDER = 0x00200000,
THEME = 0x00040000,
NOTHEME = 0x80000,
DISABLE_COOKIE = 0x400
}
[StructLayout(LayoutKind.Sequential)]
public struct DOCHOSTUIINFO
{
[MarshalAs(UnmanagedType.U4)]
public int cbSize;
[MarshalAs(UnmanagedType.I4)]
public int dwFlags;
[MarshalAs(UnmanagedType.I4)]
public int dwDoubleClick;
[MarshalAs(UnmanagedType.I4)]
public int dwReserved1;
[MarshalAs(UnmanagedType.I4)]
public int dwReserved2;
}
[StructLayout(LayoutKind.Sequential)]
public struct COMRECT
{
public int left;
public int top;
public int right;
public int bottom;
}
[StructLayout(LayoutKind.Sequential)]
public struct POINT
{
public int x;
public int y;
}
[StructLayout(LayoutKind.Sequential)]
public struct MSG
{
public IntPtr hwnd;
public int message;
public IntPtr wParam;
public IntPtr lParam;
public int time;
POINT pt;
}
[ComImport(), Guid("BD3F23C0-D43E-11CF-893B-00AA00BDCE1A"),
InterfaceTypeAttribute(ComInterfaceType.InterfaceIsIUnknown)]
public interface IDocHostUIHandler
{
[return: MarshalAs(UnmanagedType.I4)]
[PreserveSig]
int ShowContextMenu(
[In, MarshalAs(UnmanagedType.U4)]
int dwID,
[In]
ref POINT pt,
[In]
IntPtr p
