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Registering Shell Extension Handlers

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A Shell extension handler object must be registered before the Shell can use it. This topic is a general discussion of how to register a Shell extension handler.

Any time you create or change a Shell extension handler, it is important to notify the system that you have made a change. Do so by calling SHChangeNotify, specifying the SHCNE_ASSOCCHANGED event. If you do not call SHChangeNotify, the change might not be recognized until the system is rebooted.

There are some additional factors that apply to Windows 2000 systems. For details, see the Registering Shell Extension Handlers on Windows 2000 Systems section.

As with all Component Object Model (COM) objects, you must create a GUID for the handler using a tool such as Guidgen.exe, which is provided with the Windows Software Development Kit (SDK). Create a subkey under HKEY_CLASSES_ROOT\CLSID whose name is the string form of that GUID. Because Shell extension handlers are in-process servers, you also must create an InprocServer32 subkey under that GUID subkey with the (Default) value set to the path of the handler's DLL. Use the apartment threading model. An example is shown here:

HKEY_CLASSES_ROOT
   CLSID
      {00021500-0000-0000-C000-000000000046}
         InprocServer32
            (Default) = %windir%\System32\Example.dll
            ThreadingModel = Apartment

Any time the Shell takes an action that can involve a Shell extension handler, it checks the appropriate registry subkey. The subkey under which an extension handler is registered controls when it will be called. For instance, it is a common practice to have a shortcut menu handler called when the Shell displays a shortcut menu for a member of a file type. In this case, the handler must be registered under the file type's ProgID subkey.

This topic discusses the following subjects:

Handler Names

To enable a Shell extension handler, create a subkey with the handler subkey name (see below) under the ShellEx subkey of either the ProgID (for file types) or the Shell object type name (for predefined_shell_objects).

For example, if you wanted to register a shortcut menu extension handler for MyProgram.1, you begin by creating the following subkey:

HKEY_CLASSES_ROOT
   MyProgram.1
      ShellEx
         ContextMenuHandlers

For the following handlers, create a subkey underneath the "Handler Subkey name" subkey named as the string version of the class identifier (CLSID) of the Shell extension. Multiple extensions can be registered under the handler subkey name by creating multiple subkeys.

Handler Interface Handler Subkey Name
Column provider handler IColumnProvider ColumnHandlers
Shortcut menu handler IContextMenu ContextMenuHandlers
Copyhook handler ICopyHook CopyHookHandlers
Drag-and-drop handler IContextMenu DragDropHandlers
Property sheet handler IShellPropSheetExt PropertySheetHandlers

 

For the following handlers, the default value of the "Handler Subkey Name" key is the string version of the CLSID of the Shell extension. Only one extension can be registered for these handlers.

Handler Interface Handler Subkey Name
Data handler IDataObject DataHandler
Drop handler IDropTarget DropHandler
Icon handler IExtractIconA/W IconHandler
Thumbnail image handler IThumbnailProvider {E357FCCD-A995-4576-B01F-234630154E96}
Infotip handler IQueryInfo {00021500-0000-0000-C000-000000000046}
Shell link (ANSI) IShellLinkA {000214EE-0000-0000-C000-000000000046}
Shell link (UNICODE) IShellLinkW {000214F9-0000-0000-C000-000000000046}
Structured storage IStorage {0000000B-0000-0000-C000-000000000046}
Metadata IPropertySetStorage PropertyHandler
Pin to Start Menu IStartMenuPinnedList {a2a9545d-a0c2-42b4-9708-a0b2badd77c8}
Pin to Taskbar {90AA3A4E-1CBA-4233-B8BB-535773D48449}

 

The subkeys specified to add Pin to Start Menu and Pin to Taskbar to an item's shortcut menu are only required for file types that include the IsShortCut entry.

Predefined Shell Objects

The Shell defines additional objects under HKEY_CLASSES_ROOT which can be extended in the same way as file types. For example, to add a property sheet handler for all files, you can register under the PropertySheetHandlers subkey.

HKEY_CLASSES_ROOT
   *
      shellex
         PropertySheetHandlers

The following table gives the various subkeys of HKEY_CLASSES_ROOT under which extension handlers can be registered. Note that many extension handlers cannot be registered under all of the listed subkeys. For further details, see the specific handler's documentation.

Subkey Description Possible Handlers
* All files Shortcut Menu, Property Sheet, Verbs (see below)
AllFileSystemObjects All files and file folders Shortcut Menu, Property Sheet, Verbs
Folder All folders Shortcut Menu, Property Sheet, Verbs
Directory File folders Shortcut Menu, Property Sheet, Verbs
Directory\Background File folder background Shortcut Menu only
DesktopBackground Desktop background (Windows 7 and higher) Shortcut Menu, Verbs
Drive All drives in MyComputer, such as "C:\" Shortcut Menu, Property Sheet, Verbs
Network Entire network (under My Network Places) Shortcut Menu, Property Sheet, Verbs
Network\Type\# All objects of type # (see below) Shortcut Menu, Property Sheet, Verbs
NetShare All network shares Shortcut Menu, Property Sheet, Verbs
NetServer All network servers Shortcut Menu, Property Sheet, Verbs
network_provider_name All objects provided by network provider "network_provider_name" Shortcut Menu, Property Sheet, Verbs
Printers All printers Shortcut Menu, Property Sheet
AudioCD Audio CD in CD drive Verbs only
DVD DVD drive (Windows 2000) Shortcut Menu, Property Sheet, Verbs

 

Notes

  • The file folder background shortcut menu is accessed by right-clicking within a file folder, but not over any of the folder's contents.
  • "Verbs" are special commands registered under HKEY_CLASSES_ROOT\Subkey\Shell\Verb.
  • For Network\Type\#, "#" is a network provider type code in decimal. The network provider type code is the high word of a network type. The list of network types is given in the Winnetwk.h header file (WNNC_NET_* values). For example, WNNC_NET_SHIVA is 0x00330000, so the corresponding type subkey would be HKEY_CLASSES_ROOT\Network\Type\51.
  • "network_provider_name" is a network provider name as specified by WNetGetProviderName, with the spaces converted into underscores. For example, if the Microsoft Networking network provider is installed, its provider name is "Microsoft Windows Network", and the corresponding network_provider_name is Microsoft_Windows_Network.

Example of an Extension Handler Registration

To enable a particular handler, create a subkey under the extension handler type subkey with the name of the handler. The Shell does not use the handler's name, but it must be different from all other names under that type subkey. Set the default value of the name subkey to the string form of the handler's GUID.

The following example illustrates registry entries that enable shortcut menu and property sheet extension handlers, using an example .myp file type.

HKEY_CLASSES_ROOT
   .myp
      (Default) = MyProgram.1
   CLSID
      {00000000-1111-2222-3333-444444444444}
         InProcServer32
            (Default) = C:\MyDir\MyCommand.dll
            ThreadingModel = Apartment
      {11111111-2222-3333-4444-555555555555}
         InProcServer32
            (Default) = C:\MyDir\MyPropSheet.dll
            ThreadingModel = Apartment
   MyProgram.1
      (Default) = MyProgram Application
      Shellex
         ContextMenuHandler
            MyCommand
               (Default) = {00000000-1111-2222-3333-444444444444}
         PropertySheetHandlers
            MyPropSheet
               (Default) = {11111111-2222-3333-4444-555555555555}

Initializing Shell Extension Handlers