使用BackgroundWorker或调用方法（VB.net）在MainUI上更新进度栏

Question

Good day,

I need some help please. I have tried multiple methods to update a progressbar from a backgroundworker and the invoke method with no avail. I have all my code in a module which i want to access from the main ui. I start the backgroundworker from the mainform and call my procedures for the module which needs to report back to the mainforms ui (Progressbar). PBar is a public intreger that counts as the progress count for the Progress bar. BackGroundWorker:

 Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker.DoWork
    PastelGRNS(0)
    PastelRTS(0)
    PastelINVS(0)
    PastelCRNS(0)
End Sub

Private Sub BackgroundWorker_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker.ProgressChanged
    Me.PB1.Value = CInt(PBar)
End Sub

Private Sub BackgroundWorker_RunWorkerCompleted(ByVal sender As Object, _
        ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) _
        Handles BackgroundWorker.RunWorkerCompleted
    If e.Cancelled = True Then
        Alert(Me, "Canceled", "The process has been canceled.", MessageBoxButtons.OK)
    ElseIf e.Error IsNot Nothing Then
        Alert(Me, "Error", e.Error.Message, MessageBoxButtons.OK)
    Else
        Alert(Me, "Done", "All work has been completed.", MessageBoxButtons.OK)
    End If
End Sub

The Invoke ProgressBar:

  Delegate Sub SetProgress(ByVal pbar1 As Integer) 'Your delegate..
  Public Sub ChangePB(pbar1 As Integer)
    If PB1.InvokeRequired Then 
        Dim d As New SetProgress(AddressOf ChangePB)
        Me.Invoke(d, New Object() {pbar1})

    Else
         PB1.Value = pbar1
       End If


End Sub

Snipet of code to update Backgroundworker progress:

    PBar = ((cnt / ReadCnt) * 100) * 0.25
                PBar = Math.Round(PBar, 0)
                MainMenu.BackgroundWorker.ReportProgress(CInt(PBar))

my module has for processors which run i need to update my progress bar acording to the percentage ie PBar = ((cnt / ReadCnt) * 100) * 0.25 (count 25% of the full bar)

Answer 1

I'm not sure why this isn't working. The pattern is pretty simple so I suggest you break it down and find out where the issue is.

Avoid using a global variable to hold the percentage, this should just be passed in when you call ReportProgress .

Here is a fully working sample:

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    BackgroundWorker1.WorkerReportsProgress = True
    BackgroundWorker1.RunWorkerAsync()
End Sub

Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    For i As Integer = 1 To 100
        BackgroundWorker1.ReportProgress(i)
        System.Threading.Thread.Sleep(10)
    Next
End Sub

Private Sub BackgroundWorker1_ProgressChanged(sender As Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
    ProgressBar1.Value = e.ProgressPercentage
End Sub

Edit: You should not be directly updating a Progressbar in a Form from a Module. If you are then your design is wrong (you are not adhering to the Single responsibility principle).

You should do something along the lines of raising an Event that reports the progress, the subscriber than then decide what to do with this information = Thumbs up for code re-use.