Background process in vb.net

This month i started a new software, it’s a SEO Analisys Tool, and i needed to threat multithreading and background operations handling. Giving a look inside the .Net Framework i found a very interesting class, the BackgroundWorker class. First of all i have to tell you where it’s placed, in most articles on the web they forget to tell the reader where he can find it. It’s placed into the System.ComponentModel namespace.
The BackgroundWorker class is a really simple to use class, it gives you the opportunity to handle multitasking in a very easy way.

Basic informations about the class

The BackgroundWorker class exposes just few events to control the status of the process an to notify what’s going on.

1. DoWork (in this you’ll write all the code to execute)
2. ProgressChanged (raised when the thread execution process changes)
3. RunWorkerCompleted (when the thread job is finished)

All that you have to know is

1. On the top of your code page include the System.ComponentModel namespace (imports System.ComponentModel)
2. In the DoWork event write your code loop and remember to throw the ProgressChanged event if you need to handle it (RaiseEvent ProgressChanged(me)
3. Handle the process cancellation in the DoWork loop checking for CancellationPending flag (if bgWork.CancellationPending then e.cancel)
4. if you need the thread cancellation support you have to add a line of code to the New sub (bgWork.WorkerSupportsCancellation = true)

I know it seems too easy to be true but it’s really so…

Here you can find a sample piece of code to get download progress in vb.net

Or give a look at the code:

Option Strict Off
Imports System
Imports Microsoft.VisualBasic
Imports System.Windows.Forms
Imports System.Collections
Imports System.Threading
Imports System.Net
Imports System.Web.HttpUtility
Imports System.Text
Imports System.ComponentModel

Public Enum WebProcessStatus
    Idle = 0
    ReadingData = 1
    DataReady = 2
    PostingData = 3
    DataPosted = 4
    ReadingResult = 5
    ResultReady = 6
    Canceled = 7
    ErrorReading = 8
End Enum

Public Class WebProcess
    Public Status As WebProcessStatus
    Public ActionName As String
    Public URL As String
    Public lastError As String = ""
    Public sReadedHTML As String
    Public Event BeginReading()
    Public Event DataReaded(ByVal sender As Object)
    Public Event ErrorReading()
    Public Event ProgressChanged(ByVal sender As Object)
    Public progressStatus As Integer = 0
    Public WithEvents bgWork As New BackgroundWorker
    Public isCanceled As Boolean = False

    Public Sub New()
        bgWork.WorkerSupportsCancellation = True
    End Sub

    Public Sub StopProcess()
        isCanceled = True
        bgWork.CancelAsync()
    End Sub

    Public Function IsReady() As Boolean
        Select Case Status
            Case WebProcessStatus.Idle, WebProcessStatus.DataReady, WebProcessStatus.ResultReady
                Return True
            Case Else
                Return False
        End Select
    End Function

    Public Sub BeginRead()
        If Not bgWork.IsBusy Then
            progressStatus = 0
            bgWork.RunWorkerAsync()
        End If
    End Sub

    Private Sub bgWork_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgWork.DoWork
        If bgWork.CancellationPending Then
            e.Cancel = True
        End If
        RaiseEvent BeginReading()
        Try
            Dim wRemote As System.Net.WebRequest
            Dim bBuffer(999) As Byte
            Dim iBytesRead As Integer
            wRemote = System.Net.WebRequest.Create(URL)
            Dim myWebResponse As System.Net.WebResponse = wRemote.GetResponse()
            Dim scaricati As Integer
            Dim dimensione As Integer
            lastError = myWebResponse.ContentLength.ToString
            If myWebResponse.ContentLength > -1 Then
                dimensione = Convert.ToInt32(myWebResponse.ContentLength)
            Else
                dimensione = 200000
            End If
            Dim bReadedHTML(dimensione) As Byte
            Dim sw As System.IO.MemoryStream = New System.IO.MemoryStream(bReadedHTML)
            Dim sChunks As System.IO.Stream = myWebResponse.GetResponseStream
            Do
                iBytesRead = sChunks.Read(bBuffer, 0, 256)
                lastError = "1"
                scaricati += iBytesRead
                lastError = "2"
                If scaricati > dimensione Then
                    dimensione += 9062
                    ReDim bReadedHTML(dimensione)
                End If
                progressStatus = Convert.ToInt32((scaricati * 100) / dimensione)
                If iBytesRead > 0 Then
                    sw.Write(bBuffer, 0, iBytesRead)
                End If
                RaiseEvent ProgressChanged(Me)
                Application.DoEvents()
            Loop While Not (iBytesRead = 0)
            progressStatus = 100
            RaiseEvent ProgressChanged(Me)
            sChunks.Close()
            sw.Close()
            Dim objUTF8 As New UTF8Encoding()
            sReadedHTML = objUTF8.GetString(bReadedHTML)
        Catch
            sReadedHTML = ""
            progressStatus = 100
            Status = WebProcessStatus.ErrorReading
            RaiseEvent ErrorReading()
        End Try
    End Sub

    Private Sub bgWork_RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles bgWork.RunWorkerCompleted
        '  If e.Error.Message <> "" Then
        'RaiseEvent ErrorReading()
        'End If
        If Not isCanceled Then
            Status = WebProcessStatus.DataReady
        Else
            Status = WebProcessStatus.Canceled
        End If
        RaiseEvent DataReaded(Me)
    End Sub

End Class