CODEWITHSUNDEEP
vb.netbackgroundworker
NiL
NiL

Reputation: 1

BackgroundWorker will not stop

So I've searched this and other sites and I have found some hints that I think should solve my problem, but for the life of me I can't get it to work. Here's an overview. I'm working on a VB.net program that finds and lists the timestamps of files as well as their exif info if they are JPG files and populates a file list. Things work fine unless a directory has many JPG files so I decided to put the code that reads the files info into a backgound worker. My file list populate routine (lstFileList_Populate) calls the BackgroundWorker1.RunWorkerAsync. When the program starts the lstFileList_Populate gets called and when I change directory it gets called again. When it gets called the second time the BackgroundWorker1 is busy so I try to cancel it, but it never cancels. Here are some excerpts from my code.
The lstFileList_Populate:

    Private Sub lstFileList_Populate(ByVal strFileFilters As String)
         BackgroundWorker1.WorkerReportsProgress = True
         If (BackgroundWorker1.IsBusy) Then
             BackgroundWorker1.CancelAsync()
             While BackgroundWorker1.CancellationPending
                 Threading.Thread.Sleep(1000)
             End While
         End If
         BackgroundWorker1.RunWorkerAsync()
     End Sub

The Backgroundworker1_Dowork:

    Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        ' Bunch of variables defined here for the actual work

         If BackgroundWorker1.CancellationPending = True Then
             e.Cancel = True
             BackgroundWorker1.Dispose()
         Else
             ' Since code was never exiting I put this second check for CancellationPending here,
             ' and again in the for loop below but I believe it's not necessary.
             If BackgroundWorker1.CancellationPending = True Then
                 e.Cancel = True
                 BackgroundWorker1.Dispose()
             Else
                 For Each strAFileName In My.Computer.FileSystem.GetFiles(Directory.GetCurrentDirectory())
                     If BackgroundWorker1.CancellationPending = True Then
                         e.Cancel = True
                         BackgroundWorker1.Dispose()
                         Exit Sub
                     End If
                     ' The evaluation of each file gets done here in a rather long section of code
             End If
         End If
End Sub

So when the lstFileList_Populate gets called the second time the code will stay in this while loop
While BackgroundWorker1.CancellationPending
    Threading.Thread.Sleep(1000)
End While
and will never exit and, of course, if I take out the above code I get the error message that the background worker is busy. What am I doing wrong????

P.S. BTW, I don't have any training in VB or VB.net other than what I've picked up online and trained myself. I've written a few programs in VB and this is my first crack at .net so my knowledge is limited. I have spent hours researching this, but it still eludes me.

Upvotes: 0

Views: 135

Answers (1)

NiL
NiL

Reputation: 1

OK so here's the solution. I took out the timer that was suggested in the last comment and made one change to my code and things are working normally. After using the timer it appeared to me that when I was getting in the while loop below that Threading.Thread.Sleep(1000) was actually putting the BGW thread to sleep and was keeping it from cancelling it's operation. So I replaced it with Application.DoEvents() and BGW cancels right away. Here's the new code with comment:

    Private Sub lstFileList_Populate(ByVal strFileFilters As String)
     BackgroundWorker1.WorkerReportsProgress = True
     If (BackgroundWorker1.IsBusy) Then
         BackgroundWorker1.CancelAsync()
         While BackgroundWorker1.CancellationPending
' Thread sleep keeps BGW from canceling it's operation so instead use app doevent.
'                 Threading.Thread.Sleep(1000)
                 Application.DoEvents()
             End While
         End If
         BackgroundWorker1.RunWorkerAsync()
     End Sub

Many thanks for all the help and guidance.

Upvotes: -1

Related Questions