Public Class Form1
    Inherits System.Windows.Forms.Form
 
#Region " Windows Form Designer generated code "
 
    Private _stop As Boolean = False
    Private WithEvents someClass1 As SomeClass
 
    Private Delegate Sub DoSomething()
    Private Delegate Sub SetProgress(ByVal percentDone As Integer)
 
    Private iar As IAsyncResult
 
    Private Sub StartButton_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles StartButton.Click
        If iar Is Nothing Then
            Label1.Text = "Running"
            StartButton.Capture = False
            StartButton.Enabled = False
            someClass1 = New SomeClass("some parameter")
            Dim ds As New DoSomething(AddressOf someClass1.DoSomething)
            iar = ds.BeginInvoke(New AsyncCallback(AddressOf _
              DoSomethingFinished), someClass1)
        Else
            MsgBox("Function is running")
        End If
    End Sub
 
    Private Sub StopButton_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles StopButton.Click
        _stop = True
    End Sub
 
    Private Sub DoSomethingFinished(ByVal iar As IAsyncResult)
        Dim sc As SomeClass = CType(iar.AsyncState, SomeClass)
        MsgBox(sc.ToString + " finished execution")
        StartButton.Enabled = True
        init()
    End Sub
 
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles MyBase.Load
        init()
    End Sub
 
    Private Sub init()
        iar = Nothing
        ProgressBar1.Minimum = 1
        ProgressBar1.Maximum = 100
        ProgressBar1.Value = 1
        _stop = False
        Label1.Text = "Stopped"
    End Sub
 
    Private Sub someClass1_ProgressEvent(ByVal sender As Object, ByVal e As _
      SomeClassProgressEventArgs) Handles someClass1.ProgressEvent
        If Me.InvokeRequired Then
            Me.Invoke(CType(AddressOf setProgressBar, SetProgress), New Object( _
              ) {e.percentDone})
        Else
            setProgressBar(e.percentDone)
        End If
        e.Continue = Not _stop
    End Sub
 
    Private Sub setProgressBar(ByVal percentDone As Integer)
        ProgressBar1.Value = percentDone
    End Sub
End Class
 
Public Class SomeClassProgressEventArgs
    Inherits System.EventArgs
    Public Continue As Boolean
    Public percentDone As Integer
    Public Sub New(ByVal continue As Boolean, ByVal percentDone As Integer)
        Me.Continue = continue
        Me.percentDone = percentDone
    End Sub
End Class
 
Public Class SomeClass
    Public Event ProgressEvent(ByVal sender As Object, ByVal e As _
      SomeClassProgressEventArgs)
 
    Private someParameter As String
 
    Public Sub New(ByVal someParameter As String)
        Me.someParameter = someParameter
    End Sub
 
    Public Sub DoSomething()
        Dim continue As Boolean = True
        Dim percentDone As Integer = 1
        While continue AndAlso percentDone < 100
            Dim evArgs As New SomeClassProgressEventArgs(True, percentDone)
            RaiseEvent ProgressEvent(Me, evArgs)
            continue = evArgs.Continue
            If continue Then
                ' Tue was immer...
                percentDone += 1
                System.Threading.Thread.Sleep(100)
            End If
        End While
    End Sub
 
    Public Overrides Function ToString() As String
        Return "SomeClass for: " + someParameter
    End Function
End Class