Modified event of FileSystemWatcher getting triggered multiple times

Question

I want to monitor the following

New File being created/copied to the directory
Existing file edited

I use the following code to subscribe to the created and changed event of the FileSystemWatcher class.I have noted some issues with FSW Class.

On replacing files, the changed event is getting triggered numerous times.

How can i get over this issue.Kindly advice.

 watcher.Path = watchpath;
 watcher.Filter = "*.*";
 watcher.Created += new FileSystemEventHandler(copied);
 watcher.Changed += new FileSystemEventHandler(Watcher_Changed);
 watcher.NotifyFilter = NotifyFilters.LastWrite;
 watcher.EnableRaisingEvents = true;

For a single item copied to the folder,the following events are raised

  *******> Created 
    -----> Changed 
    -----> Changed

Because multiple things changed. File contents. File last-modified time. etc. — Raymond Chen, Mar 06 '19 at 03:42
There is nothing to fix. The FileSystemWatcher is behaving as designed. The file changed twice. — Raymond Chen, Mar 06 '19 at 05:35
@RaymondChen Well its not behaving as expected even after adding `watcher.NotifyFilter = NotifyFilters.LastWrite;` For 8 files,the event is triggered more than 8 times. — techno, Mar 06 '19 at 05:39
Redundant notifications are within spec. The purpose of the FileSystemWatcher is to let you monitor a directory listing so you can maintain a cached copy. The event tells you to go refresh your cache. Redundant refresh requests are allowed. The system doesn't say "Oh, wait, somebody updated the last-write time, and it's the same as the previous last-write time, so I'll suppress the notification." If somebody updates the last-write time, it raises the event, even if they updated it to the same value it already had. — Raymond Chen, Mar 06 '19 at 15:06

score 0 · Answer 1 · answered Mar 06 '19 at 05:21

0

Yes, that is expected as already mentioned in the comments. Also have a look at : FileSystemWatcher Changed event is raised twice

to have a workaround you will need to add a dictionary which will track the raised events for every files.

Dictionary<string, DateTime> lastWriteDate //fileName - Last write date time

and in changed event you will have to handle it like below,

    private static void Watcher_Changed(object sender, System.IO.FileSystemEventArgs e)
    {
        string filePath = e.FullPath;
        DateTime writeDate = System.IO.File.GetLastWriteTime(filePath);
        if (lastWriteDate.ContainsKey(filePath))
        {
            if (lastWriteDate[filePath] == writeDate) 
                //Exit as we already have raised an event for this
                return;
            lastWriteDate[filePath] = writeDate;
        }
        else
        {
            lastWriteDate.Add(filePath, writeDate);
        }

        //Do your stuff.
    }

answered Mar 06 '19 at 05:21

Amit

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Thanks but for 8 files,the event is getting triggered 13 times. – techno Mar 06 '19 at 05:42
Can you implement this in your test code, I believe this should be able to "return" multiple events raise. Let me know the observation. – Amit Mar 06 '19 at 05:49
I managed to solve the issue by using this answer from the referred post https://stackoverflow.com/a/23287926/848968 – techno Mar 06 '19 at 06:15
@techno very well, kindly extract the answer from that Git Repo solution and post it here, who knows when that user just delete that repo. – Amit Mar 06 '19 at 06:18
This question has been flagged for duplicate. – techno Mar 06 '19 at 06:22

Modified event of FileSystemWatcher getting triggered multiple times

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