[Updated on 2011-4-2: In .NET 4, with the ability to have multiple runtimes in process with any other runtime, writing managed shell extensions becomes possible.  However, Microsoft has not fully tested all of the scenarios involved with managed shell extensions and has not determined whether it will support managed shell extensions for the long term.  Therefore, Microsoft will not support managed shell extensions and recommends against writing them.. I will update this blog article if it becomes officially supported in future.]

In "Writing Windows Shell Extension with .NET Framework 4 (C#, VB.NET) - Part 1: Context Menu Handler", we introduced how to write Windows shell context menu handler using .NET 4:

Lots of developers have this follow-up question: how can I add bitmap icons to those context menu items? 

Here you are the directly working code samples from Microsoft All-In-One Code Framework!

Implementation Details

The menu items in the context menu were added in the implementation of IContextMenu.QueryContextMenu:

        public int QueryContextMenu(
            IntPtr hMenu,
            uint iMenu,
            uint idCmdFirst,
            uint idCmdLast,
            uint uFlags)
        {
            ......
            // Use either InsertMenu or InsertMenuItem to add menu items.
            MENUITEMINFO mii = new MENUITEMINFO();
            mii.cbSize = (uint)Marshal.SizeOf(mii);
            mii.fMask = MIIM.MIIM_STRING | MIIM.MIIM_FTYPE | MIIM.MIIM_ID | MIIM.MIIM_STATE;
            mii.wID = idCmdFirst + IDM_DISPLAY;
            mii.fType = MFT.MFT_STRING;
            mii.dwTypeData = this.menuText;
            mii.fState = MFS.MFS_ENABLED;
            if (!NativeMethods.InsertMenuItem(hMenu, iMenu, true, ref mii))
            {
                return Marshal.GetHRForLastWin32Error();
            }
            ......
       }

The MENUITEMINFO structure supports displaying a bitmap next to the menu item text.  You just need to add the MIIM_BITMAP mask in MENUITEMINFO.fMask, and point MSENUITEMINFO.hbmpItem to the HBITMAP handle of a 16x16 bitmap. The modified code is as follows.

        public int QueryContextMenu(
            IntPtr hMenu,
            uint iMenu,
            uint idCmdFirst,
            uint idCmdLast,
            uint uFlags)
        {
            ......
            // Use either InsertMenu or InsertMenuItem to add menu items.
            MENUITEMINFO mii = new MENUITEMINFO();
            mii.cbSize = (uint)Marshal.SizeOf(mii);
            mii.fMask = MIIM.MIIM_BITMAP | MIIM.MIIM_STRING | MIIM.MIIM_FTYPE |
                MIIM.MIIM_ID | MIIM.MIIM_STATE;
            mii.wID = idCmdFirst + IDM_DISPLAY;
            mii.fType = MFT.MFT_STRING;
            mii.dwTypeData = this.menuText;
            mii.fState = MFS.MFS_ENABLED;
            mii.hbmpItem = this.menuBmp;
            if (!NativeMethods.InsertMenuItem(hMenu, iMenu, true, ref mii))
            {
                return Marshal.GetHRForLastWin32Error();
            }
            ......
        }

The "this.menuBmp" is initialized in the constructor of the context menu extension class:

        public FileContextMenuExt()
        {
            // Load the bitmap for the menu item.
            Bitmap bmp = Resources.OK;  // A 16x16 bmp added to the Resources of the project.
            bmp.MakeTransparent(bmp.GetPixel(0, 0));
            this.menuBmp = bmp.GetHbitmap();
        }

And the handle is released in the destructor of the class:

        ~FileContextMenuExt()
        {
            if (this.menuBmp != IntPtr.Zero)
            {
                NativeMethods.DeleteObject(this.menuBmp);
                this.menuBmp = IntPtr.Zero;
            }
        }

With these modifications, the context menu extension will display menu items with bitmap icons.

NOTE:

1. Do release the HBITMAP handle created by Bitmap.GetHbitmap. 
A common mistake is as follows.  It will leak the bitmap handle.

            // Use either InsertMenu or InsertMenuItem to add menu items.
            MENUITEMINFO mii = new MENUITEMINFO();
            mii.cbSize = (uint)Marshal.SizeOf(mii);
            mii.fMask = MIIM.MIIM_BITMAP | MIIM.MIIM_STRING | MIIM.MIIM_FTYPE |
                MIIM.MIIM_ID | MIIM.MIIM_STATE;
            mii.wID = idCmdFirst + IDM_DISPLAY;
            mii.fType = MFT.MFT_STRING;
            mii.dwTypeData = this.menuText;
            mii.fState = MFS.MFS_ENABLED;
            mii.hbmpItem = Resources.OK.GetHbitmap();  // This will leak the bitmap handle!
            if (!NativeMethods.InsertMenuItem(hMenu, iMenu, true, ref mii))
            {
                return Marshal.GetHRForLastWin32Error();
            }

 2. Do not set MFT_BITMAP in MENUITEMINFO.fType. 
The MFT_BITMAP type is for a different bitmap purpose.  It displays the menu item using a bitmap. The low-order word of the dwTypeData member is the bitmap handle. For example,