Nrthugu

I am trying to use a single handler to cover the end of multiple backgroundworker activities and cannot find a way to get the information about the specific backgroundworker using the backgroundworkercompleted event.
My code to catch the event is as below:

Private Sub BGx_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted, BackgroundWorker2.RunWorkerCompleted, BackgroundWorker3.RunWorkerCompleted, BackgroundWorker4.RunWorkerCompleted, BackgroundWorker5.RunWorkerCompleted, BackgroundWorker6.RunWorkerCompleted, BackgroundWorker7.RunWorkerCompleted, BackgroundWorker8.RunWorkerCompleted



    'Do work here based on completed Backgroundworker



    For BG = 1 To 8

        If Not DSWorkers(BG).IsBusy Then

            If DStatus(BG) = -2 Then : DStatus(BG) = -1 : End If

        End If

    Next



    Complete()

End Sub

There is nothing on the "Do Work Here" section because I do not know how to capture and have been unable to find details of the backgroundworkercompleted event id.

Please - any pointers as to how I can identify the specific completed BackgroundWorker

As with all event handlers, the sender parameter is a reference to the object that raised the event, so you can access the actual BackgroundWorker that has completed its work via that. If you need some data other than that, you assign it to the e.Result property in the DoWork event handler and get it back from the e.Result property in the RunWorkerCompleted event handler. e.Result works for getting data out of the DoWork event handler much as e.Argument works for getting data in.

Check this out for some examples of using BackgroundWorker objects, including passing data out using e.Result. You might also like to checkout my own BackgroundMultiWorker class, which basically combines the functionality of multiple BackgroundWorker objects into a single BackgroundMultiWorker object. It identifies each task using a token.

EDIT:

Here's an example that may help with this issue and your task in general:

Imports System.ComponentModel

Imports System.Threading



Public Class Form1



    Private ReadOnly resultsByWorker As New Dictionary(Of BackgroundWorker, BackgroundWorkerResult)

    Private ReadOnly rng As New Random



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

        'The NumericUpDown is used to select the index of a BackgroundWorker to cancel.

        With NumericUpDown1

            .DecimalPlaces = 0

            .Minimum = 0

            .Maximum = 9

        End With

    End Sub



    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        'Create 10 BackgroundWorkers and run them.

        For i = 1 To 10

            Dim worker As New BackgroundWorker



            resultsByWorker.Add(worker, New BackgroundWorkerResult)



            AddHandler worker.DoWork, AddressOf workers_DoWork

            AddHandler worker.RunWorkerCompleted, AddressOf workers_RunWorkerCompleted



            worker.WorkerSupportsCancellation = True



            worker.RunWorkerAsync()

        Next

    End Sub



    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

        Dim index = Convert.ToInt32(NumericUpDown1.Value)

        Dim worker = resultsByWorker.Keys.ToArray()(index)



        If worker.IsBusy Then

            'Cancel the BackgroundWorker at the specified index.

            worker.CancelAsync()

        End If

    End Sub



    Private Sub workers_DoWork(sender As Object, e As DoWorkEventArgs)

        Dim worker = DirectCast(sender, BackgroundWorker)



        'Do work for a random number of seconds between 10 and 20.

        Dim period = rng.Next(10, 20 + 1)



        For i = 0 To period

            If worker.CancellationPending Then

                e.Cancel = True

                Return

            End If



            'Simulate work.

            Thread.Sleep(1000)

        Next



        'The work was completed without being cancelled.

        e.Result = period

    End Sub



    Private Sub workers_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs)

        Dim worker = DirectCast(sender, BackgroundWorker)

        Dim result = resultsByWorker(worker)



        If e.Cancelled Then

            result.WasCancelled = True

        Else

            result.Result = CInt(e.Result)

        End If



        Dim workers = resultsByWorker.Keys.ToArray()



        If Not workers.Any(Function(bgw) bgw.IsBusy) Then

            'All work has completed so display the results.



            Dim results As New List(Of String)



            For i = 0 To workers.GetUpperBound(0)

                worker = workers(i)

                result = resultsByWorker(worker)



                results.Add($"Worker {i} {If(result.WasCancelled, "was cancelled", $"completed {result.Result} iterations")}.")

            Next



            MessageBox.Show(String.Join(Environment.NewLine, results))

        End If

    End Sub

End Class



Public Class BackgroundWorkerResult

    Public Property WasCancelled As Boolean

    Public Property Result As Integer

End Class

Here is that example reworked to use a single instance of the BackgroundMultiWorker is linked to instead of multiple instances of the BackgroundWorker class.

Imports System.Threading



Public Class Form1



    Private WithEvents worker As New BackgroundMultiWorker With {.WorkerSupportsCancellation = True}

    Private ReadOnly results(9) As BackgroundWorkerResult

    Private ReadOnly rng As New Random



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

        'The NumericUpDown is used to select the index of a BackgroundWorker to cancel.

        With NumericUpDown1

            .DecimalPlaces = 0

            .Minimum = 0

            .Maximum = results.GetUpperBound(0)

        End With

    End Sub



    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        'Create 10 BackgroundWorkers and run them.

        For i = 0 To results.GetUpperBound(0)

            results(i) = New BackgroundWorkerResult



            worker.RunWorkerAsync(i)

        Next

    End Sub



    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

        Dim index = Convert.ToInt32(NumericUpDown1.Value)



        If worker.IsBusy(index) Then

            'Cancel the BackgroundWorker at the specified index.

            worker.CancelAsync(index)

        End If

    End Sub



    Private Sub worker_DoWork(sender As Object, e As DoWorkEventArgs) Handles worker.DoWork

        'Do work for a random number of seconds between 10 and 20.

        Dim period = rng.Next(10, 20 + 1)



        For i = 0 To period

            If worker.IsCancellationPending(e.Token) Then

                e.Cancel = True

                Return

            End If



            'Simulate work.

            Thread.Sleep(1000)

        Next



        'The work was completed without being cancelled.

        e.Result = period

    End Sub



    Private Sub workers_RunWorkerCompleted(sender As Object, e As RunWorkerCompletedEventArgs) Handles worker.RunWorkerCompleted

        Dim result = results(CInt(e.Token))



        If e.Cancelled Then

            result.WasCancelled = True

        Else

            result.Result = CInt(e.Result)

        End If



        If Not worker.IsBusy() Then

            'All work has completed so display the results.



            Dim output As New List(Of String)



            For i = 0 To results.GetUpperBound(0)

                result = results(i)



                output.Add($"Task {i} {If(result.WasCancelled, "was cancelled", $"completed {result.Result} iterations")}.")

            Next



            MessageBox.Show(String.Join(Environment.NewLine, output))

        End If

    End Sub

End Class



Public Class BackgroundWorkerResult

    Public Property WasCancelled As Boolean

    Public Property Result As Integer

End Class