SHChangeNotifyRegister function (shlobj_core.h)

Article
10/13/2021

Registers a window to receive notifications from the file system or Shell, if the file system supports notifications.

Syntax

ULONG SHChangeNotifyRegister(
  [in] HWND                      hwnd,
       int                       fSources,
       LONG                      fEvents,
       UINT                      wMsg,
       int                       cEntries,
  [in] const SHChangeNotifyEntry *pshcne
);

Parameters

[in] hwnd

Type: HWND

A handle to the window that receives the change or notification messages.

fSources

Type: int

One or more of the following values that indicate the type of events for which to receive notifications.

Note In earlier versions of the SDK, these flags are not defined in a header file and implementers must define these values themselves or use their numeric values directly. As of Windows Vista, these flags are defined in Shlobj.h.

SHCNRF_InterruptLevel (0x0001)

Interrupt level notifications from the file system.

SHCNRF_ShellLevel (0x0002)

Shell-level notifications from the shell.

SHCNRF_RecursiveInterrupt (0x1000)

Interrupt events on the whole subtree. This flag must be combined with the SHCNRF_InterruptLevel flag. When using this flag, notifications must also be made recursive by setting the fRecursive member of the corresponding SHChangeNotifyEntry structure referenced by pshcne to TRUE. Use of SHCNRF_RecursiveInterrupt on a single level view—for example, a PIDL that is relative and contains only one SHITEMID—will block event notification at the highest level and thereby prevent a recursive, child update. Thus, an icon dragged into the lowest level of a folder hierarchy may fail to appear in the view as expected.

SHCNRF_NewDelivery (0x8000)

Messages received use shared memory. Call SHChangeNotification_Lock to access the actual data. Call SHChangeNotification_Unlock to release the memory when done.

Note We recommend this flag because it provides a more robust delivery method. All clients should specify this flag.

fEvents

Type: LONG

Change notification events for which to receive notification. See the SHCNE flags listed in SHChangeNotify for possible values.

wMsg

Type: UINT

Message to be posted to the window procedure.

cEntries

Type: int

Number of entries in the pshcne array.

[in] pshcne

Type: const SHChangeNotifyEntry*

Array of SHChangeNotifyEntry structures that contain the notifications. This array should always be set to one when calling SHChangeNotifyRegister or SHChangeNotifyDeregister will not work properly.

Return value

Type: ULONG

Returns a positive integer registration ID. Returns 0 if out of memory or in response to invalid parameters.

Remarks

See the Change Notify Watcher Sample in the Windows Software Development Kit (SDK) for a full example that demonstrates the use of this function.

When a change notification event is raised, the message indicated by wMsg is delivered to the window specified by the hwnd parameter.

If SHCNRF_NewDelivery is specified, the wParam and lParam values in the message should be passed to SHChangeNotification_Lock as the hChange and dwProcID parameters respectively.
If SHCNRF_NewDelivery is not specified, wParam is a pointer to two PIDLIST_ABSOLUTE pointers, and lParam specifies the event. The two PIDLIST_ABSOLUTE pointers can be NULL, depending on the event being sent.

When a relevant file system event takes place and the hwnd parameter is not NULL, then the message indicated by wMsg is posted to the specified window. Otherwise, if the pshcne parameter is not NULL, then that notification entry is used.

For performance reasons, multiple notifications can be combined into a single notification. For example, if a large number of SHCNE_UPDATEITEM notifications are generated for files in the same folder, they can be joined into a single SHCNE_UPDATEDIR notification.

The NTSHChangeNotifyRegister function, which is no longer available as of Windows Vista, was equivalent to SHChangeNotifyRegister with the SHCNRF_NewDelivery flag.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	shlobj_core.h (include Shlobj.h)
Library	Shell32.lib
DLL	Shell32.dll (version 5.0 or later)
API set	ext-ms-win-shell-shell32-l1-2-1 (introduced in Windows 10, version 10.0.10240)

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