How to use filesystemwatcher and send mail every time a file is created in a folder?

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There is a process we are running, which creates files and writes data on a particular event. File is created in folder: C:\\EventListenerFolder\\ . Now whenever a new file is created and data is written to the file, we need to send a mail.

public static void RunEventListenerPrgm()
{
//the mail notification has to go as a file gets generated in C:\\EventListenerFolder\\
while (true)
{
System.IO.FileSystemWatcher m_Watcher = new System.IO.FileSystemWatcher();
m_Watcher.Filter = "*.txt";
m_Watcher.Path = "C:\\EventListenerFolder\\";
m_Watcher.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite | NotifyFilters.FileName | NotifyFilters.DirectoryName;
m_Watcher.Changed += new FileSystemEventHandler(OnChanged);
m_Watcher.EnableRaisingEvents = true;
}
}

public static void OnChanged(object sender, FileSystemEventArgs e)
{
string stringReceived;
string[] allFiles = System.IO.Directory.GetFiles("C:\\EventListenerFolder\\");
foreach (string file in allFiles)
{
Console.WriteLine("EventListener Match File Found. FILE NAME : " + file);
try
{
stringReceived = System.IO.File.ReadAllText(file);
}
catch (Exception ex)
{
continue; // to avoid reading of file when it is in process of being written . hence we wait till the file is written and then we read it
}
SendMailFunction(stringReceived);
File.Delete(file);

}
}

In this scenario, we are getting 100+ mail for the same file. And we want only one mail for one file to be sent.

What I have tried:

Tried changing m_Watcher.Changed += new FileSystemEventHandler(OnChanged);
to m_Watcher.Created+= new FileSystemEventHandler(OnChanged);
still doesnot work.

Could it be that the file watcher event Filter I am using is incorrect?
Could you please help me on the same?

Posted 21-Sep-17 4:26am

Member 10536462

Updated 21-Sep-17 7:07am

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Richard Deeming · Answer 1 · 2017-09-21T07:07:00

So many problems; where to begin? :)

Your OnChanged event handler is ignoring the information about which file changed, and sending a notification for all files in the folder. You should use e.FullName to process just the file which has changed:

C#

private static void OnChanged(object sender, FileSystemEventArgs e)
{
    string file = e.FullName;
    Console.WriteLine("EventListener Match File Found. FILE NAME : {0}", file);
    
    try
    {
        string stringReceived = File.ReadAllText(file);
        SendMailFunction(stringReceived);
        File.Delete(file);
    }
    catch (IOException)
    {
    }
}

Your RunEventListenerPrgm method is creating multiple new FileSystemWatcher instances in a tight loop. Every single instance you create is going to trigger the OnChanged handler every time a file is changed. I'm amazed that you only managed to receive hundreds of messages for a single file!

The method will never terminate cleanly, so a quick-and-dirty fix would be to move the creation of the FileSystemWatcher instance outside of the loop:

C#

public static void RunEventListenerPrgm()
{
    var m_Watcher = new System.IO.FileSystemWatcher
    {
        Filter = "*.txt",
        Path = @"C:\EventListenerFolder\",
        NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite | NotifyFilters.FileName | NotifyFilters.DirectoryName
    };
    
    m_Watcher.Created += OnChanged;
    m_Watcher.EnableRaisingEvents = true;
    
    while (true)
    {
    }
}

However, this will probably consume 100% of one of your CPU cores all the time the program is running!

A slightly better alternative would be to use the WaitForChanged method:

C#

public static void RunEventListenerPrgm()
{
    var m_Watcher = new System.IO.FileSystemWatcher
    {
        Filter = "*.txt",
        Path = @"C:\EventListenerFolder\",
        NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite | NotifyFilters.FileName | NotifyFilters.DirectoryName
    };
    
    while (true)
    {
        WaitForChangedResult result = m_Watcher.WaitForChanged(WatcherChangeTypes.Created | WatcherChangeTypes.Changed);
        if (!result.TimedOut)
        {
            OnChanged(result.Name);
        }
    }
}

private static void OnChanged(string file)
{
    Console.WriteLine("EventListener Match File Found. FILE NAME : {0}", file);
    
    try
    {
        string stringReceived = File.ReadAllText(file);
        SendMailFunction(stringReceived);
        File.Delete(file);
    }
    catch (IOException)
    {
    }
}

Ideally, you'd need to find some way to notify the method when your application was closing, so that it could stop the loop cleanly.

Finally, there is a known issue where the FileSystemWatcher can generate multiple events for the same change. There are numerous workarounds to be found - for example:
FileSystemWatcher Changed event is raised twice - Stack Overflow[^]
FileSystemWatcher generates duplicate events – How to workaround – BizTalk 2006 – Windows SharePoint Services adapter[^]