How can I make sure this is the last change in FileSystemWatcher onChanged event?

Question

I am using FileSystemWatcher to read the contents of a file that is written to by another application. The events that happen are as follows:

1. First, the onCreated event happens.
2. Then, the onChanged event happens, an unknown number of times (sometimes it's 2, sometimes it's 3, and sometimes it's 4).

Is there a trick to know, in the handler for the onChanged event, that this is the last time this file is being written to by the other application?

Answer 1

Any duplicated OnChanged events from the FileSystemWatcher can be detected and discarded by checking the File.GetLastWriteTime timestamp on the file in question. Like so:

Private lastRead As DateTime = DateTime.MinValue

Private Sub OnChanged(source As Object, a As FileSystemEventArgs)
    Dim lastWriteTime As DateTime = File.GetLastWriteTime(uri)
    If lastWriteTime <> lastRead Then
        doStuff()
        lastRead = lastWriteTime
    End If
    ' else discard the (duplicated) OnChanged event
End Sub

Another approach is discussed here