最近在做Windows shell extension 的开发工作，对shell extension handler的注册机制有点疑问，以下摘自MSDN：http://msdn.microsoft.com/en-us/library/windows/desktop/cc144067(v=vs.85).aspx
Registering Shell Extension Handlers
A Shell extension handler object must be registered before the Shell can use it. This section 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 with SHChangeNotify, specifying the SHCNE_ASSOCCHANGED event. If you do not call SHChangeNotify, the change might not be recognized until the system is rebooted.
As with all COM objects, you must create a GUID for the handler using a tool such as UUIDGEN.exe. Create a key under HKEY_CLASSES_ROOTCLSID whose name is the string form of the GUID. Because Shell extension handlers are in-process servers, you must create an InProcServer32 key under the GUID key with the default value set to the path of the handler's DLL. Use the Apartment threading model.
Any time the Shell takes an action that can involve a Shell extension handler, it checks the appropriate registry key. The key under which an extension handler is registered thus 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 key.
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 would 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" key whose name is the string version of the CLSID of the Shell extension. Multiple extensions can be registered under the handler subkey name key by creating multiple subkeys.
| Handler | Interface | Handler Subkey Name |
|---|---|---|
| Shortcut menu handler | IContextMenu | ContextMenuHandlers |
| Copyhook handler | ICopyHook | CopyHookHandlers |
| Drag-and-drop handler | IContextMenu | DragDropHandlers |
| Property sheet handler | IShellPropSheetExt | PropertySheetHandlers |
| Column provider handler (deprecated in Windows Vista) | IColumnProvider | ColumnHandlers |
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 |
| Image handler | IExtractImage | {BB2E617C-0920-11d1-9A0B-00C04FC2D6C1} |
| 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 | IPropertyStore | PropertyHandler |
| Metadata | IPropertySetStorage (deprecated in Windows Vista) | 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.
Support for column provider handlers was removed in Windows Vista. Also, as of Windows Vista,IPropertySetStorage has been deprecated in favor of IPropertyStore.
While IExtractImage remains supported, IThumbnailProvider is preferred for Windows Vista and later.
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 thePropertySheetHandlers key.
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 | Version |
|---|---|---|---|
| * | All files | Shortcut Menu, Property Sheet, Verbs (see below) | All |
| AllFileSystemObjects | All files and file folders | Shortcut Menu, Property Sheet, Verbs | 4.71 |
| Folder | All folders | Shortcut Menu, Property Sheet, Verbs | All |
| Directory | File folders | Shortcut Menu, Property Sheet, Verbs | All |
| DirectoryBackground | File folder background | Shortcut Menu only | 4.71 |
| Drive | All drives in MyComputer, such as "C:" | Shortcut Menu, Property Sheet, Verbs | All |
| Network | Entire network (under My Network Places) | Shortcut Menu, Property Sheet, Verbs | All |
| NetworkType# | All objects of type # (see below) | Shortcut menu, Property Sheet, Verbs | 4.71 |
| NetShare | All network shares | Shortcut menu, Property Sheet, Verbs | 4.71 |
| NetServer | All network servers | Shortcut menu, Property Sheet, Verbs | 4.71 |
| network_provider_name | All objects provided by network provider "network_provider_name" | Shortcut menu, Property Sheet, Verbs | All |
| Printers | All printers | Shortcut Menu, Property Sheet | All |
| AudioCD | Audio CD in CD drive | Verbs only | All |
| DVD | DVD drive (Windows 2000) | Shortcut Menu, Property Sheet, Verbs | 4.71 |
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_ROOTSubkeyShellVerb .
- For NetworkType# , "#" 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 key would be HKEY_CLASSES_ROOTNetworkType51 .
- "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 correspondingnetwork_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 key 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:MyDirMyCommand.dll
ThreadingModel = Apartment
{11111111-2222-3333-4444-555555555555}
InProcServer32
(Default) = C:MyDirMyPropSheet.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}
The registration procedure discussed in this section must be followed for all Windows systems.