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File changed notification

Posted on 2000-05-07
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Last Modified: 2013-11-20
Hi,
I need to do the following in my MDI application:
If the file associated with the active view changes by other application then when the user returns to my application
one message box must warn this.

I have think to do the following: Save the modified time and each the OnSetFocus message is sent to the view, compare it with a new modified time reading.
The problem is that this message is always being sent after the message box ends. More each window in my application that loses focus to my view will trigger this message.
Can I filter this to only accept OnSetFocus from alien windows?
Is there a better way to spy file changes?

I am looking for comments on my solution and of course how to solve the problem if this is the right way to do things.
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Question by:lsimaozinho
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3 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 200 total points
ID: 2786003
The easiest way to do this is opening a notification handle for this file in a separate thread and send a message to your application when the file is modified, e.g.

('pseudocode', error checking omitted for brevity)

HANDLE      g_hFileWatcher;
DWORD       g_dwTID;

    g_hFileWatcher  =   CreateThread    (   NULL,
                                            0,
                                            FileWatcher,
                                            (PVOID) "c:\\docs\\whatever.txt",
                                            0,
                                            &g_dwTID
                                        );


int WINAPI FileWatcher  (   LPVOID  pv)
{
    HANDLE  hNotify;
    DWORD   dwWaitResult;
    char*   pszFile =   ( char*) pv;

    OutputDebugString   (   "FileWatcher(): here i am!!!\n");

    hNotify =   FindFirstChangeNotification (   pszFile,
                                                FALSE,
                                                FILE_NOTIFY_CHANGE_SIZE | FILE_NOTIFY_CHANGE_LAST_WRITE
                                            );

    if  (   INVALID_HANDLE_VALUE    ==  hNotify)
            OutputDebugString   (   "Error acquiring handle file!!!\n");

    for (   ;;)
        {
            dwWaitResult    =   WaitForSingleObject (   hNotify,
                                                        INFINITE
                                                    );

            if  (   WAIT_ABANDONED  ==  dwWaitResult)
                    return( dwWaitResult);

            OutputDebugString   (   "FileWatcher(): there has been some change...\n");

            SendMessage ( WM_THEFILEHASCHANGED, ...)

            FindNextChangeNotification  (   hNotify);
        };

    return( 0);
}

Feel free to ask if you need more information!
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LVL 86

Expert Comment

by:jkr
ID: 2786097
Ooops, forgot something - be sure to insert 'CloseHandle ( hNotify);' before the 'return' statement... Sorry ;-)
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Author Comment

by:lsimaozinho
ID: 2786109
Thanks jkr
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