I am trying to implement an Icon Overlay Handler in C#.
So far I have come up with the following code.
After registering the dll with regasm I get icon overlays all over the place
just as requested.
The problem is that a different icon is displayed as overlay than the
iconFile I
pass in te GetOverlayInfo methode.
Running the whole thing through the debugger I can see that on entering the
GetOverlayInfo methode the iconFileBuffer
is already filled and although I change it the "older" iconFile is used.
This leads me to the conclusion that I dealing with a string marshalling
problem. Switching to StringBuilder doesn't correct it.
Anyone?

using System;
using System.Runtime.InteropServices;
using Microsoft.Win32;

namespace ShellExtension
{

   public sealed class ShellInterop
   {

       private ShellInterop()
       {
       }

       /*
        * void SHChangeNotify(
        *     LONG wEventId,
        *     UINT uFlags,
        *     LPCVOID dwItem1,
        *     LPCVOID dwItem2);
        */
       [DllImport("shell32.dll")]
       public static extern void SHChangeNotify(
           int      eventID,
           uint    flags,
           IntPtr item1,
           IntPtr item2);

   }

   [ComVisible(false)]
   [ComImport]
   [Guid("0C6C4200-C589-11D0-999A-00C04FD655E1")]
   [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
   public interface IShellIconOverlayIdentifier
   {

       [PreserveSig]    int IsMemberOf(
           [MarshalAs(UnmanagedType.LPWStr)]    string path,

uint attributes);

       [PreserveSig]    int GetOverlayInfo(
           [MarshalAs(UnmanagedType.LPWStr)]    string iconFileBuffer,

int     iconFileBufferSize,

out int iconIndex,

out uint flags);

       [PreserveSig]    int GetPriority(
           out int priority);

   }

   [ComVisible(true)]
   [Guid("B8FA9E43-38E6-4654-8A13-FF905AD22CE5")]
   public class MyIconOverlay:IShellIconOverlayIdentifier
   {

       #region IShellIconOverlayIdentifier Members

       public int IsMemberOf(string path, uint attributes)
       {
           //Show everything with icon overlay
           return 0; // S_OK
       }

       public int GetOverlayInfo(string iconFileBuffer, int
iconFileBufferSize, out int iconIndex, out uint flags)
       {
           iconFileBuffer = @"c:\overlay.ico";
           iconIndex = 0;
           flags = 1; // ISIOI_ICONFILE
           return 0; // S_OK
       }

       public int GetPriority(out int priority)
       {
           priority = 0; // 0-100 (0 is highest priority)
           return 0; // S_OK
       }

       #endregion

       #region Registry

       [ComRegisterFunction]
       public static void Register(Type t)
       {
           RegistryKey rk =
Registry.LocalMachine.CreateSubKey(@"SOFTWARE\Microsoft\Windows\CurrentVersi
on\Explorer\ShellIconOverlayIdentifiers\_" + t.Name);
           rk.SetValue(string.Empty, t.GUID.ToString("B").ToUpper());
           rk.Close();
           ShellInterop.SHChangeNotify(0x08000000, 0, IntPtr.Zero,
IntPtr.Zero);
       }

       public static void Unregister(Type t)
       {

Registry.LocalMachine.DeleteSubKeyTree(@"SOFTWARE\Microsoft\Windows\CurrentV
ersion\Explorer\ShellIconOverlayIdentifiers\_" + t.Name);
           ShellInterop.SHChangeNotify(0x08000000, 0, IntPtr.Zero,
IntPtr.Zero);
       }

       #endregion

   }

}