The following table shows the return values for this function.

Success indicates that the caller will be notified every time the specified value changes and the specified condition are true. Failure does not cause any change.

For a client to differentiate between multiple notifications, the msgparameter should be unique for each call to RegistryNotifyWindowmade by a client.

To stop notification and to close the notification handle, the caller must call RegistryCloseNotification. However, this type of notification is transient. Resetting the device stops the notification.

When pszValueNamechanges, PostMessagenotifies the client. If PostMessagefails or if hWndis no longer valid, then the registered notification request is removed and phNotifyhandle is closed. The following table shows the parameters passed to PostMessage.

If the value does not exist when RegistryNotifyWindowis called, then the client will be notified when the value is added.

This function can be used to monitor any registry key in the system. The header file snapi.h contains definitions for the registry keys, paths, values, and bitmasks for all the base notifications that are provided by the system.

If the key specified by hKeyand pszSubKeydoesn't exist, then hKeyis monitored until pszSubKeyis created, after which pszSubKeyis monitored and changes to the key will trigger notifications as requested. To minimize possible performance degradation stemming from a large nuimber of subkeys being monitored, it is a best practice to pass (as hKey) the handle to a key that's as close as possible to pszSubKeyrather than passing a root key. For example, if the client is a game and it is monitoring the key structure HKEY_CURRENT_USER\...\MyCoolGame\Player1 and the game could later create HKEY_CURRENT_USER\...\MyCoolGame\Player2, two possible ways to approach notification of changes to the Player2 key include:

The following code example demonstrates how to use RegistryNotifyWindow.

Note:
To make the following code example easier to read, security checking and error handling are not included. This code example should not be used in a release configuration unless it has been modified to include them.

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// Register to be notified when the next Appointment location changes, // and contains the string "Downtown". LRESULT RegistryNotifyWindowProc(HWND hDlg, UINT msg, UINT wParam, LONG lParam) { TCHAR szLocation[256]; NOTIFICATIONCONDITION nc; LRESULT lRet = FALSE; HREGNOTIFY hNotify = NULL; TCHAR szDowntown[] = TEXT("Downtown"); switch (msg) { case WM_CREATE: // Initialize the notification structure // Note that StatStor is not case sensitive. nc.ctComparisonType = REG_CT_CONTAINS; nc.TargetValue.psz = szDowntown; // A value of zero indicates a string comparison. nc.dwMask = 0; RegistryNotifyWindow(SN_CALENDARNEXTAPPOINTMENTLOCATION_ROOT, SN_CALENDARNEXTAPPOINTMENTLOCATION_PATH, SN_CALENDARNEXTAPPOINTMENTLOCATION_VALUE, hDlg, WM_USER, 0, &nc, &hNotify); lRet = 0; break; case WM_USER: // You can read the full location with the RegistryGetString function. RegistryGetString(SN_CALENDARNEXTAPPOINTMENTLOCATION_ROOT, SN_CALENDARNEXTAPPOINTMENTLOCATION_PATH, SN_CALENDARNEXTAPPOINTMENTLOCATION_VALUE, szLocation, 256); // Add your own processing statements here. lRet = TRUE; break; case WM_DESTROY: RegistryCloseNotification(hNotify); lRet = 0; break; // Add your own statements for handling other messages, here. return lRet;