FileSystemWatcher in arraylist

FileSystemWatcher in arraylist

• Daggs

  Thanks for your help, Paul. You were right in suspecting the object in the array was null.

  I had forgotten to mention that the file monitoring was working correctly - it was when i tried to change properties that i got the exception, and that's what puzzled me.

  Anyway, the problem was a silly little oversight. My watcher creator is a function of type FileSystemWatcher. I forgot to put a return statement!

  return myWatch
  ' problem solved:)

  and that's why, kids, you have to practice every now and then or you'll get rusty.

  
  
  

• Sameer Bhangar - MSFT

  Hi Mark,

  Your approach and code so far looks right.

  One problem you might have is that your procedure added a FileSystemWatcher object to the ArrayList, but that object was not successfully initialized. A simple example is if you create a FileSystemWatcher passing in a path that does not exist, e.g. "Dim w as FileSystemWatcher = new FileSystemWatcher("c:\pathdoesnotexist"). If you have no error handling then you will immediately hit an exception. If you do trap the exception, then w gets added to your ArrayList even though it is Null/Nothing.

  What you can do is protect against this situation by checking to see if your FileSystemWatcher object is Nothing before adding it to the ArrayList. It's also nice to trap any exceptions that happen when you create it.

  Here is a code sample that works for me:

  Public Class Form1

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

  'create 2 file system watchers

  Me.CreateWatcherForPath("C:\Windows\")

  Me.CreateWatcherForPath("C:\Temp\")

  '--now watchlist has 2 items

  'test changing properties

  Dim w As IO.FileSystemWatcher

  w = Me.watchList(0)

  w.Path = "c:\other\"

  w.EnableRaisingEvents = False

  Stop

  End Sub

  Friend watchList As New ArrayList

  Private Sub CreateWatcherForPath(ByVal path As String)

  'create new FileSystemWatcher object with defaults

  Dim fsw As IO.FileSystemWatcher

  Try

  fsw = New IO.FileSystemWatcher(path)

  fsw.EnableRaisingEvents = True

  Catch ex As Exception

  My.Application.Log.WriteEntry("Could not create FSW for path: " & path)

  End Try

  'check for null in case the FSW could not initialize

  If fsw IsNot Nothing Then

  'add it to the ArrayList; watchList.Count increases by 1

  Me.watchList.Add(fsw)

  End If

  End Sub

  Private Sub FileSystemWatcher1_Changed(ByVal sender As Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed

  Debug.WriteLine("fs1 changed: " & e.Name)

  End Sub

  End Class

  Hope this helps.

  Best,

  Paul Yuknewicz

  VB Program Manager

  
  

• Brandon Bray

  You bet. I'm glad you uncovered the problem.

  One note is that you should see a Green squiggly / compiler warning in VB 2005 if you forget to have a Return in a function. This might help in the future - we all forget these things sometimes.

  
  

• Jacob Christ

  Followed the example and I seend to have everything working (on the array side)

   

  The problem is my script isn't tracking any events. Nothing is being triggered

   

   

  'Get Sources button events
  Private Sub btnGetSources_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGetSources.Click

  Call getsources()

  End Sub

   

  Public Sub getsources()

  conSQL.Open()

  cmdGetSources.CommandText = "SELECT * FROM Sources"
  drSources = cmdGetSources.ExecuteReader()

  With drSources

  if .HasRows Then

  While .Read
  ListBox1.Items.Add(.Item(1))
  createwatchers(.Item(1))
  End While

  End If

  End With

  drSources.Close()

  conSQL.Close()

  End Sub

   

  Private Sub createwatchers(ByVal e As String)

  'http://forums.microsoft.com/MSDN/ShowPost.aspx PostID=224039&SiteId=1

  Dim fsw_watcher As FileSystemWatcher

  'Create filesystemwatcher and set property values.

  Try

  fsw_watcher = New FileSystemWatcher(e)
  fsw_watcher.IncludeSubdirectories = True
  fsw_watcher.EnableRaisingEvents = True
  fsw_watcher.NotifyFilter = NotifyFilters.FileName & NotifyFilters.DirectoryName

  Catch ex As Exception

  MessageBox.Show("Error occured, check application log")
  My.Application.Log.WriteEntry("QVBServ Could not create a FileSystemWatcher for path: " & e & ". Directory Doesn't Exist")

  End Try

  If fsw_watcher IsNot Nothing Then

  'add it to the ArrayList; watchList.Count increases by 1
  watcherArray.Add(fsw_watcher)
  fswCount.Text = watcherArray.Count
  'Dim arraytype As String = watcherArray.GetType.ToString()

  End If

  End Sub

   

   

  Private Sub FileSystemWatcher1_Changed(ByVal sender As Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed

  lbfileresults.Items.Add(e.Name & " " & e.ChangeType)

  End Sub

   

  Private Sub fsw_watcher_Changed(ByVal sender As Object, ByVal e As System.IO.FileSystemEventArgs) Handles fsw_watcher.Changed

  lbfileresults.Items.Add(e.Name & " " & e.ChangeType)

  End Sub

  Forgive the formatting, couldn't find the codeblock tag

  
  
• FileSystemWatcher in arraylist