CODEWITHSUNDEEP
vb.netwinformsfilesystemwatcher
Dwight Schrute
Dwight Schrute

Reputation: 369

FileSystemWatcher odd behaviour

Imports System.IO

  Public Class Form1
   Dim watcher As New FileSystemWatcher()
   Dim FileChanged As Boolean
   Delegate Sub UpdateFileChangeDelegate()


   Private Sub Button_Click(sender As System.Object, e As System.EventArgs) Handles Button.Click
    watcher.Path = "C:\Demo Image Pool"
    watcher.NotifyFilter = NotifyFilters.LastWrite
    watcher.Filter = "DemoImage.raw"
    watcher.SynchronizingObject = Me
    AddHandler watcher.Changed, AddressOf OnChanged
    watcher.EnableRaisingEvents = True
    TextBoxMessage.Text = "Looking for file change"

    'The code below relates to Application
    Dim myProcess As New Process()
    myProcess.StartInfo.FileName = "CaptureImage.exe"
    myProcess.StartInfo.Arguments = "60 500 8 100"
    myProcess.StartInfo.UseShellExecute = False
    myProcess.StartInfo.CreateNoWindow = True
    myProcess.StartInfo.RedirectStandardInput = True
    myProcess.StartInfo.RedirectStandardOutput = True
    myProcess.StartInfo.RedirectStandardError = True

    myProcess.Start()
    myProcess.WaitForExit(28000)
    myProcess.Close()

    While 1
        If FileChanged = True Then
            TextBoxMessage.Text = "Hello World"
            Exit While
        End If
    End While

 End Sub

 Private Shared Sub OnChanged(ByVal source As Object, ByVal e As FileSystemEventArgs)
    Form1.FileChanged = True
 End Sub

End Class

In the above code, the CaptureImage.exe captures a new image, "DemoImage.raw", at the FileWatcher location. I am changing the Boolean variable to true in the File Change event handler, however in the main thread, I am not able to get out of the loop. The reason being, I think, variable FileChanged being not changed or the change being not reflected. I would greatly appreciate if someone can point out where I have gone wrong. The form consists of simply a button and textbox.

Thanks!

Upvotes: 0

Views: 84

Answers (1)

jmcilhinney
jmcilhinney

Reputation: 54417

The problem is that you're using a default instance and default instances are thread-specific. As such, you're actually creating a new Form1 instance and setting its field rather than the Form1 instance that you have open. No form should refer to its own default instance anyway, so that should be Me.FileChanged rather than Form1.FileChanged.

Apart from that, I really hope that is just some really dirty testing code because you have a busy wait loop there and that's about the worst code you can possibly write.

Upvotes: 1

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