Windows CE: CeRegGetNotificationInfo() Doesn’t Seem to Work

I am writing this with a sense of defeat. In my post about monitoring for registry changes (see Windows CE: Monitor for Registry Changes) I showed how to monitor for registry changes using CeFindFirstRegChange() and CeFindNextRegChange() but left the code for determining what changed empty. Honestly, I gave it a shot with the new function CeRegGetNotificationInfo() available in Windows CE 6.0. I simply cannot get it to work, and my searching on the WEB didn’t turn up anything that tells me that it does work (unless you count the MSDN documentation.)

So, I decided to post the code here for review and would love to hear from you if you have suggestions. The following code fits into the monitor code that I posted earlier.

RETAILMSG( 1, (TEXT("Found reg change\r\n")));

if( CeRegGetNotificationInfo( hFind, 0, NULL, 0, NULL, &BytesAvailable ) )

RETAILMSG( 1, (TEXT("CeRegGetNotificationInfo failed %d\r\n"), GetLastError() ));

RETAILMSG( 1, (TEXT("Bytes Available %X\r\n"), BytesAvailable ));

if( BytesAvailable == 0 )

RETAILMSG( 1, (TEXT("No data\r\n")));

if( !CeRegGetNotificationInfo( NULL, 0, NULL, 0, NULL, NULL ) )

RETAILMSG( 1, (TEXT("CeRegGetNotificationInfo failed %d\r\n"), GetLastError() ));

if( !CeRegGetNotificationInfo( hFind, 0, NULL, 0, NULL, NULL ) )

RETAILMSG( 1, (TEXT("CeRegGetNotificationInfo failed %d\r\n"), GetLastError() ));

BytesAvailable = 1024;

RegInfo = (REG_NOTIFY_INFORMATION *)malloc( BytesAvailable );

if( RegInfo && !CeRegGetNotificationInfo( hFind, 0, RegInfo, BytesAvailable, &BytesReturned, &BytesAvailable ) )

{

RETAILMSG( 1, (TEXT("BA %d BR %d\r\n"), BytesAvailable, BytesReturned ));

NextRegInfo = RegInfo;

while( NextRegInfo->NextEntryOffset )

{

switch( NextRegInfo->Action )

{

case FILE_ACTION_ADDED:

RETAILMSG( 1, (TEXT("Action Added\r\n")));

break;

case FILE_ACTION_MODIFIED:

RETAILMSG( 1, (TEXT("Action Modified\r\n")));

break;

case FILE_ACTION_REMOVED:

RETAILMSG( 1, (TEXT("Action Deleted\r\n")));

break;

}

if( NextRegInfo->RegNameLength )

{

TCHAR *RegStr = (TCHAR *)malloc((NextRegInfo->RegNameLength + 1 ) * sizeof(TCHAR));

wcsncpy( RegStr, NextRegInfo->RegName, NextRegInfo->RegNameLength );

RegStr[ NextRegInfo->RegNameLength ] = '\0';

RETAILMSG( 1, (TEXT("Changed %s\r\n"), RegStr ));

free( RegStr );

}

NextRegInfo = (REG_NOTIFY_INFORMATION*)( (DWORD)NextRegInfo + NextRegInfo->NextEntryOffset );

}

else

RETAILMSG( 1, (TEXT("CeGetFileNotificationInfo failed\r\n")));

free( RegInfo );

CeFindNextRegChange( hFind );

The new variable declarations are:

REG_NOTIFY_INFORMATION *RegInfo;

REG_NOTIFY_INFORMATION *NextRegInfo;

DWORD BytesAvailable = 0xa5a5;

DWORD BytesReturned;

You will notice some oddities in the code above. I tried to get it to fail by calling CeRegGetNotificationInfo() with all invalid parameters, and it does fail with an invalid handle returned by GetLastError(). But if I pass in a valid handle and the other parameters as invalid, it succeeds. But, I should point out that I had to ignore the documentation and look for zero for failure and non-zero for success – or actually it seems that it only returns zero.

Finally, I tried forcing the allocation of data, but still no results.

I have posted a follow up: Windows CE: CeRegGetNotificationInfo() Doesn’t Seem to Work Part 2

Your Comments.

# re: Windows CE: CeRegGetNotificationInfo() Doesn’t Seem to Work
Hi Bruce,

A google for 'CeFindFirstRegChange' shows that multiple people have the same negative results as you. Some suggestions:

- A fellow on xd-developers said he was experiencing a very slow system and cured it by using RegCreateKeyEx instead of RegOpenKeyEx. Worth a test.

- Try using a different Registry tree than hklm\Drivers.

- Try waiting for a specific key to change and then have a second app change that key's value.

Also, it looks like a logic error on the line:

if( RegInfo && !CeRegGetNotificationInfo( hFind, 0, RegInfo, BytesAvailable, &BytesReturned, &BytesAvailable ) )

As CeRegGetNotificationInfo() returns non-zero for success, removing the '!' might be the ticket.

Actual working sample code from MS would be very nice. Good luck!

++ Todd

Left by Todd MacMillan at 8/19/2009 3:56 PM